Internet DRAFT - draft-pinkas-smime-cades
draft-pinkas-smime-cades
S/MIME Working Group J.Ross(Security and Standards)
INTERNET-DRAFT N.Pope(Security and Standards)
Expires February 2006 D.Pinkas(Bull)
Obsoletes: RFC 3126 August 2005
Target Category: Informational
CMS Advanced Electronic Signatures (CAdES)
<draft-pinkas-smime-cades-01.txt>
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Abstract
This document defines the format of an electronic signature that can
remain valid over long periods. This includes evidence as to its
validity even if the signer or verifying party later attempts to deny
(i.e., repudiates the validity of the signature). The format can be
considered as an extension to RFC 3369 and RFC 2634, where, when
appropriate additional signed and unsigned attributes have been
defined. The contents of this Informational RFC amounts to a
transposition of the ETSI TS 101 733 V.1.6.3 (CMS Advanced
Electronic Signatures - CAdES) and is technically equivalent to it.
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Table of Contents
1. Introduction 6
2. Scope 6
3. Definitions and abbreviations 8
3.1 Definitions 8
3.2 Abbreviations 11
4. Overview 12
4.1 Major parties 12
4.2 Signatures policies 14
4.3 Electronic signature formats 14
4.3.1 CAdES Basic Electronic Signature (CAdES-BES) 14
4.3.2 CAdES Explicit Policy Electronic Signatures (CAdES-EPES) 17
4.4 Electronic signature formats with validation data 18
4.4.1 Electronic Signature with Time (CAdES-T) 19
4.4.2 ES with Complete validation data references (CAdES-C) 20
4.4.3 Extended electronic signature formats 22
4.4.4 Archival Electronic Signature (CAdES-A) 26
4.5 Arbitration 27
4.6 Validation process 28
5. Electronic signature attributes 29
5.1 General syntax 29
5.2 Data content type 29
5.3 Signed-data content type 29
5.4 SignedData type 30
5.5 EncapsulatedContentInfo type 30
5.6 SignerInfo type 30
5.6.1 Message digest calculation process 31
5.6.2 Message signature generation process 31
5.6.3 Message signature verification process 31
5.7 Basic ES mandatory present attributes 31
5.7.1 Content type 31
5.7.2 Message digest 31
5.7.3 Signing certificate reference attribute 31
5.8 Additional mandatory attributes for Explicit Policy-based
Electronic Signatures 33
5.8.1 Signature policy identifier 33
5.9 CMS imported optional attributes 35
5.9.1 Signing time 35
5.9.2 Countersignature 35
5.10 ESS imported optional attributes 36
5.10.1 Content reference attribute 36
5.10.2 Content identifier attribute 36
5.10.3 Content hints attribute 36
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5.11 Additional optional attributes defined in the present document 37
5.11.1 Commitment type indication attribute 37
5.11.2 Signer location attribute 39
5.11.3 Signer attributes attribute 40
5.11.4 Content time-stamp 40
5.12 Support for multiple signatures 41
5.12.1 Independent signatures 41
5.12.2 Embedded signatures 41
6. Additional Electronic Signature validation attributes 41
6.1 Electronic Signature Time-stamped (CAdES-T) 43
6.1.1 Signature time- stamp attribute definition 43
6.2 Complete validation reference data (CAdES-C) 44
6.2.1 Complete certificate references attribute definition 44
6.2.2 Complete Revocation References attribute definition 45
6.2.3 Attribute certificate references attribute definition 47
6.2.4 Attribute revocation references attribute definition 47
6.3 Extended validation data (CAdES-X) 48
6.3.1 Time-stamped validation data (CAdES-X Type 1 or Type 2) 48
6.3.2 Long validation data (CAdES-X Long, CAdES-X Long Type 1 or 2) 48
6.3.3 Certificate values attribute definition 49
6.3.4 Revocation values attribute definition 50
6.3.5 CAdES-C time-stamp attribute definition 51
6.3.6 Time-stamped certificates and crls references attribute
definition 51
6.4 Archive validation data 52
6.4.1 Archive time-stamp attribute definition 52
7. Other standard data structures 54
7.1 Public-key certificate format 54
7.2 Certificate revocation list format 54
7.3 OCSP response format 54
7.4 Time-stamp token format 54
7.5 Name and attribute formats 54
7.6 Attribute certificate 55
8. Conformance requirements 55
8.1 CAdES-Basic Electronic Signature (CAdES-BES) 56
8.2 CAdES-Explicit Policy-based Electronic Signature 56
8.3 Verification using time-stamping 56
8.4 Verification using secure records 57
9. Security considerations 58
9.1 Protection of private key 58
9.2 Choice of algorithms 58
10. IANA Considerations 58
11. References 58
11.1 Normative references 58
11.2 Informative references 59
12. Authors' addresses 62
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Annex A (normative): ASN.1 definitions 63
A.1 Signature format definitions using X.208 ASN.1 syntax 63
A.2 Signature format definitions using X.680 ASN.1 syntax 72
Annex B (informative): Extended forms of Electronic Signatures 81
B.1 Extended forms of validation data 81
B.1.1 CAdES-X Long 82
B.1.2 CAdES-X Type 1 83
B.1.3 CAdES-X Type 2 84
B.1.4 CAdES-X Long Type 1 and CAdES-X Long Type 2 85
B.2 Timestamp extensions 87
B.3 Archive validation data (CAdES-A) 88
B.4 Example validation sequence 90
B.5 Additional optional features 95
Annex C (informative):General description 96
C.1 The signature policy 96
C.2 Signed information 97
C.3 Components of an electronic signature 97
C.3.1 Reference to the signature policy 97
C.3.2 Commitment type indication 98
C.3.3 Certificate identifier from the signer 98
C.3.4 Role attributes 99
C.3.4.1 Claimed role 99
C.3.4.2 Certified role 100
C.3.5 Signer location 100
C.3.6 Signing time 100
C.3.7 Content format 101
C.3.8 Content cross referencing 101
C.4 Components of validation data 101
C.4.1 Revocation status information 101
C.4.1.1 CRL information 102
C.4.1.2 OCSP information 102
C.4.2 Certification path 103
C.4.3 Time-stamping for long life of signatures 103
C.4.4 Time-stamping for long life of signature before CA key
compromises 104
C.4.4.1 Time-stamping the ES with complete validation data 105
C.4.4.2 Time-stamping certificates and revocation information
references 106
C.4.5 Time-stamping for archive of signature 107
C.4.6 Reference to additional data 108
C.4.7 Time-stamping for mutual recognition 108
C.4.8 TSA key compromise 109
C.5 Multiple signatures 109
Annex D (informative):Data protocols to interoperate with TSPs 110
D.1 Operational protocols 110
D.1.1 Certificate retrieval 110
D.1.2 CRL retrieval 110
D.1.3 OnLine certificate status 110
D.1.4 Time-stamping 110
D.2 Management protocols 110
D.2.1 Request for certificate revocation 110
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Annex E (informative): Guidance on naming 111
E.1 Allocation of names 111
E.2 Providing access to registration information 111
E.3 Naming schemes 112
E.3.1 Naming schemes for individual citizens 112
E.3.2 Naming schemes for employees of an organization 113
Annex F (informative): Example structured contents and MIME 114
F.1 General description 114
F.2 Header information 114
F.3 Content encoding 115
F.4 Multi-part content 115
F.5 S/MIME 116
Annex G (informative): Relationship to the European Directive
And EESSI 119
G.1 Introduction 119
G.2 Electronic signatures and the directive 119
G.3 ETSI electronic signature formats and the directive 120
G.4 EESSI standards and classes of electronic signature 120
G.4.1 Structure of EESSI standardization 120
G.4.2 Classes of electronic signatures 121
G.4.3 EESSI classes and the ETSI electronic signature format 121
Annex H (informative): APIs for the generation and verification
of electronic signatures tokens 122
H.1 Data framing 122
H.2 IDUP-GSS-APIs defined by the IETF 123
H.3 CORBA security interfaces defined by the OMG 124
Annex I (informative):Cryptographic algorithms 126
I.1 Digest algorithms 126
I.1.1 SHA-1 126
I.1.2 General 126
I.2 Digital signature algorithms 127
I.2.1 DSA 127
I.2.2 RSA 127
I.2.3 General 128
Annex J (informative): Changes from the previous version 130
Full Copyright Statement 131
Disclaimer 131
Intellectual Property 131
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1. Introduction
This document is intended to cover electronic signatures for various
types of transactions, including business transactions (e.g. purchase
requisition, contract, and invoice applications) where long term
validity of such signatures is important. This includes evidence as
to its validity even if the signer or verifying party later attempts
to deny (i.e., repudiates, see ISO/IEC 10181-5) the validity of the
signature).
Thus the present document can be used for any transaction between an
individual and a company, between two companies, between an individual
and a governmental body, etc. The present document is independent of
any environment. It can be applied to any environment e.g. smart cards,
GSM SIM cards, special programs for electronic signatures, etc.
The European Directive on a community framework for Electronic
Signatures defines an electronic signature as: "Data in electronic form
which is attached to or logically associated with other electronic data
and which serves as a method of authentication".
An electronic signature as used in the present document is a form
of advanced electronic signature as defined in the Directive.
The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in this document (in uppercase,
as shown) are to be interpreted as described in RFC 2119 [STDWORDS]
2. Scope
The scope the present document covers Electronic Signature Formats
only. The aspects of Electronic Signature Policies are defined in RFC
3125 and in TR 102 272 (see informative references).
The present document defines a number of Electronic Signature Formats,
including electronic signature that can remain valid over long periods.
This includes evidence as to its validity even if the signer or
verifying party later attempts to deny (repudiates) the validity of the
electronic signature.
The present document specifies use of trusted service providers (e.g.
Time-Stamping Authorities), and the data that needs to be archived
(e.g. cross certificates and revocation lists) to meet the requirements
of long term electronic signatures.
An electronic signature defined by the present document can be used for
arbitration in case of a dispute between the signer and verifier, which
may occur at some later time, even years later.
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The present document includes the concept of signature policies that
can be used to establish technical consistency when validating
electronic signatures but does not mandate their use.
The present document is based on the use of public key cryptography to
produce digital signatures, supported by public key certificates.
The present document also specifies the use of time-stamping and time-
marking services to prove the validity of a signature long after the
normal lifetime of critical elements of an electronic signature. It
also, as an option, defines ways to provide very long-term protection
against key compromise or weakened algorithms.
The present document builds on existing standards that are widely
adopted. This includes:
- RFC 3852 [4] "Cryptographic Message Syntax (CMS)";
- ISO/IEC 9594-8/ITU-T Recommendation X.509 [1]: "Information
technology - Open Systems Interconnection - The Directory:
Authentication framework";
- RFC 3280 [2] "Internet X.509 Public Key Infrastructure (PKIX)
Certificate and CRL Profile";
- RFC 3161 [7] "Internet X.509 Public Key Infrastructure Time-Stamp
Protocol (TSP)".
NOTE: See section 11 for a full set of references.
The present document describes formats for advanced electronic
signatures using ASN.1 (Abstract Syntax Notation 1). These formats are
based on CMS (Cryptographic Message Syntax) defined in RFC 3852 [4].
These electronic signatures are thus called CAdES, for "CMS Advanced
Electronic Signatures".
Another document, TS 101 903 (see informative references), describes
formats for XML advanced electronic signatures (XAdES) built on
XMLDSIG.
In addition, the present document identifies other documents that
define formats for Public Key Certificates, Attribute Certificates,
Certificate Revocation Lists and supporting protocols, including,
protocols for use of trusted third parties to support the operation of
electronic signature creation and validation.
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Informative annexes include:
- illustrations of extended forms of extended Electronic Signatures
formats that protect against various vulnerabilities and examples
of validation processes;
- descriptions and explanations of some of the concepts used in the
present document. giving a rational for normative parts of the
present document;
- information on protocols to interoperate with Trusted Service
Providers;
- information on security considerations;
- an example structured content and MIME;
- the relationship between the present document and the directive
on electronic signature and associated standardization
initiatives;
- APIs to support the generation and the verification of electronic
signatures;
- cryptographic algorithms that may be used;
- guidance on naming.
- changes from the previous version.
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the following terms and
definitions apply:
Arbitrator: arbitrator entity may be used to arbitrate a dispute
between a signer and verifier when there is a disagreement on the
validity of a digital signature.
Attribute Authority (AA): authority which assigns privileges by issuing
attribute certificates.
Authority certificate: certificate issued to an authority (e.g. either
to a certification authority or to an attribute authority).
Attribute Authority Revocation List (AARL): revocation list containing
a list of references to certificates issued to AAs, that are no longer
considered valid by the issuing authority.
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Attribute Certificate Revocation List (ACRL): revocation list
containing a list of references to attribute certificates that are no
longer considered valid by the issuing authority.
Certification Authority Revocation List (CARL): revocation list
containing a list of public-key certificates issued to certification
authorities, that are no longer considered valid by the certificate
issuer.
Certification Authority (CA): authority trusted by one or more users to
create and assign public key certificates, optionally the certification
authority may create the users' keys.
NOTE: See ITU-T Recommendation X.509 [1].
Certificate Revocation List (CRL): signed list indicating a set of
public key certificates that are no longer considered valid by the
certificate issuer.
Digital signature: data appended to, or a cryptographic transformation
of, a data unit that allows a recipient of the data unit to prove the
source and integrity of the data unit and protect against forgery, e.g.
by the recipient.
NOTE: See ISO 7498-2 (see informative references).
Electronic signature: data in electronic form which are attached to or
logically associated with other electronic data and which serve as a
method of authentication.
NOTE: See Directive 1999/93/EC of the European Parliament and of the
Council of 13 December 1999 on a Community framework for
electronic signatures.
Enhanced electronic signatures: electronic signatures enhanced by
complementing the baseline requirements with additional data, such as
time tamp tokens and certificate revocation data, to address commonly
recognized threats.
Explicit Policy-based Electronic Signature (EPES): an electronic
signature where the signature policy is explicitly specified that shall
be used to validate it.
grace period: time period which permits the certificate revocation
information to propagate through the revocation process to relying
parties.
Initial verification: a process performed by a verifier done after an
electronic signature is generated in order to capture additional
information that could make it valid for long term verification.
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Public Key Certificate (PKC): public keys of a user, together with some
other information, rendered unforgeable by encipherment with the
private key of the certification authority which issued it.
NOTE: See ITU-T Recommendation X.509 [1].
Rivest-Shamir-Adleman (RSA): asymmetric cryptography algorithm based on
the difficulty to factorize very large numbers, using a key pair: a
private key and a public key.
Signature policy: set of rules for the creation and validation of an
electronic signature, that defines the technical and procedural
requirements for electronic signature creation and validation, in order
to meet a particular business need, and under which the signature can
be determined to be valid.
Signature policy issuer: entity that defines and issues a signature
policy.
Signature validation policy: part of the signature policy which
specifies the technical requirements on the signer in creating a
signature and verifier when validating a signature.
Signer: entity that creates an electronic signature.
Subsequent Verification: a process performed by a verifier to assess
the signature validity.
NOTE: It may be done even years after the electronic signature was
produced by the signer and completed by the Initial
Verification and it might not need to capture more data than
those captured at the time of initial verification.
Time-Stamp token: data object that binds a representation of a datum to
a particular time, thus establishing evidence that the datum existed
before that time.
Time-Mark: information in an audit trail from a Trusted Service
Provider that binds a representation of a datum to a particular time,
thus establishing evidence that the datum existed before that time.
Time-Marking Authority: trusted third party that creates records in an
audit trail in order to indicate that a datum existed before a
particular point in time.
Time-Stamping Authority (TSA): trusted third party that creates time-
stamp tokens in order to indicate that a datum existed at a particular
point in time.
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Time-Stamping Unit (TSU): set of hardware and software which is managed
as a unit and has a single time-stamp token signing key active at a
time.
Trusted Service Provider (TSP): entity that helps to build trust
relationships by making available or providing some information upon
request.
Validation data: additional data that may be used by a verifier of
electronic signatures to determine the signature is valid.
Valid electronic signature: electronic signature which passes
validation.
Verifier: entity that verifies evidence.
NOTE 1: See ISO/IEC 13888-1 (see informative references).
NOTE 2: Within the context of the present document this is an entity
that validates an electronic signature.
3.2 Abbreviations
For the purposes of the present document, the following abbreviations
apply:
AA Attribute Authority
AARL Attribute Authority Revocation List
ACRL Attribute Certificate Revocation List
API Application Program Interface
ASCII American Standard Code for Information Interchange
ASN.1 Abstract Syntax Notation 1
CA Certification Authority
CAD Card Accepting Device
CAdES CMS Advanced Electronic Signature
CAdES-A CAdES with Archive validation data
CAdES-BES CAdES Basic Electronic Signature
CAdES-C CAdES with Complete validation data
CAdES-EPES CAdES Explicit Policy Electronic Signature
CAdES-T CAdES with Time-stamp
CAdES-X CAdES with eXtended validation data
CARL Certification Authority Revocation List
CMS Cryptographic Message Syntax
CRL Certificate Revocation List
CWA CEN Workshop Agreement
DER Distinguished Encoding Rules (for ASN.1)
DSA Digital Signature Algorithm
EDIFACT Electronic Data Interchange For Administration, Commerce
and Transport
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EESSI European Electronic Signature Standardization Initiative
EPES Explicit Policy-based Electronic Signature
ES Electronic Signature
ESS Enhanced Security Services (enhances CMS)
IDL Interface Definition Language
MIME Multipurpose Internet Mail Extensions
OCSP Online Certificate Status Provider
OID Object IDentifier
PKC Public Key Certificate
PKIX internet X.509 Public Key Infrastructure
RSA Rivest-Shamir-Adleman
SHA-1 Secure Hash Algorithm 1
TSA Time-Stamping Authority
TSP Trusted Service Provider
TST Time-Stamp Token
TSU Time-Stamping Unit
URI Uniform Resource Identifier
URL Uniform Resource Locator
XML eXtended Mark up Language
XMLDSIG XML-Signature Syntax and Processing
4 Overview
The present document defines a number of Electronic Signature (ES)
formats that build on CMS (RFC 3852 [4] by adding signed and unsigned
attributes.
This clause provides an introduction to the major parties involved
(clause 4.1), the concept of Signature Policies (clause 4.2), provides
an overview of the various ES formats (clause 4.3), introduces the
concept of validation data and provides an overview of formats that
incorporate validation data (clause 4.4), presents relevant
considerations on arbitration (clause 4.5) and for the validation
process (clause 4.6).
The formal specifications of the attributes are specified in clauses 5
and 6, annexes C and D provide rationale for the definitions of the
different ES forms.
4.1 Major parties
The major parties involved in a business transaction supported by
electronic signatures as defined in the present document are:
- the Signer;
- the Verifier;
- Trusted Service Providers (TSP);
- the Arbitrator.
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The signer is the entity that creates the electronic signature. When
the signer digitally signs over data using the prescribed format, this
represents a commitment on behalf of the signing entity to the data
being signed.
The verifier is the entity that validates the electronic signature, it
may be a single entity or multiple entities.
The Trusted Service Providers (TSPs) are one or more entities that help
to build trust relationships between the signer and verifier. They
support the signer and verifier by means of supporting services
including: user certificates, cross-certificates, time-stamp tokens,
CRLs, ARLs, OCSP responses. The following TSPs are used to support the
functions defined in the present document:
- Certification Authorities;
- Registration Authorities;
- Repository Authorities (e.g. a Directory);
- Time-Stamping Authorities;
- Time-Marking Authorities;
- Signature Policy Issuers.
Certification Authorities provide users with public key certificates
and with a revocation service.
Registration Authorities allow the identification and registration of
entities before a CA generates certificates.
Repository Authorities publish CRLs issued by CAs, signature policies
issued by Signature Policy Issuers and optionally public key
certificates.
Time-Stamping Authorities attest that some data was formed before a
given trusted time.
Time-Marking Authorities record that some data was formed before a
given trusted time.
Signature Policy Issuers define the signature policies to be used by
signers and verifiers.
In some cases the following additional TSPs are needed:
- Attribute Authorities.
Attributes Authorities provide users with attributes linked to public
key certificates.
An Arbitrator is an entity that arbitrates in disputes between a signer
and a verifier.
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4.2 Signatures policies
The present document includes the concept of signature policies that
can be used to establish technical consistency when validating
electronic signatures.
When a comprehensive signature policy used by the verifier is either
explicitly indicated by the signer or implied by the data being signed,
then a consistent result can be obtained when validating an electronic
signature.
When the signature policy being used by the verifier is neither
indicated by the signer nor can be derived from other data, or the
signature policy is incomplete then verifiers, including arbitrators,
may obtain different results when validating an electronic signature.
Therefore, comprehensive signature policies that ensure consistency of
signature validation are recommended from both the signers and
verifiers point of view.
Further information on signature policies is provided in:
- TR 102 038 (see informative references);
- Clauses 5.8.1, C.1 and C.3.1 of the present document;
- RFC 3125 (see informative references);
- TR 102 272 (see informative references).
4.3 Electronic signature formats
The current clause provides an overview for two forms of CMS advanced
electronic signature specified in the present document, namely, the
CAdES Basic Electronic Signature (CAdES-BES) and the CAdES Explicit
Policy-based Electronic Signature (CAdES-EPES). Conformance to the
present document mandates the signer creates one of these formats.
4.3.1 CAdES Basic Electronic Signature (CAdES-BES)
A CAdES Basic Electronic Signature (CAdES-BES) in accordance with the
present contains:
- The signed user data (e.g. the signer's document) as defined in
CMS (RFC 3852 [4]);
- A collection of mandatory signed attributes as defined in CMS
(RFC 3852 [4]).and in ESS (RFC 2634 [5]);
- Additional mandatory signed attributes defined in the present
document;
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- The digital signature value computed on the user data and, when
present, on the signed attributes, as defined in CMS (RFC 3852
[4]).
A CAdES Basic Electronic Signature (CAdES-BES) in accordance with the
present may contain:
- A collection of additional signed attributes;
- A collection of optional unsigned attributes.
The mandatory signed attributes are:
- Content-type. It is defined in RFC 3852 [4] and specifies that
the content type of the ContentInfo is "signed-data". Details
are provided in clause 5.7.1;
- Message-digest. It is defined in RFC 3852 [4] and specifies the
message digest of the eContent OCTET STRING within
encapContentInfo being signed. Details are provided in clause
5.7.2;
- ESS signing-certificate OR other-signing-certificate. The ESS
signing-certificate attribute is defined in Enhanced Security
Services (ESS), RFC 2634 [5] and only allows for the use of SHA-1
as digest algorithm. The other-signing-certificate attribute one
is defined in the present document and allows for the use of any
digest algorithm. A CAdES-BES claiming compliance with the
present document must include one of them. Clause 5.7.3 provides
the details of these attributes. Clause 5.7.3.2 shows the formal
specification of other-signing-certificate. Rationale for its
inclusion is provided in clause C.3.3.
Optional signed attributes may be added to the CAdES-BES, including
optional signed attributes defined in CMS (RFC 3852 [4]), (RFC 2634
[5]) and the present document. Listed below are optional attributes
that are defined in clause 5 and have a rational provided in annex C:
- Signing-time: as defined in CMS (RFC 3852 [4]) indicates the time
of the signature as claimed by the signer. Details and short
rationale are provided in clause 5.9.1. Clause C.3.6 in provides
the rationale.
- Content-hints as defined in ESS (RFC 2634 [5]) provides
information that describes the format of the signed content.
Clause 5.10.1 provides the specification details. Clause C.3.7
in provides the rationale.
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- Content-reference. as defined in ESS (RFC 2634 [5]) can be
incorporated as a way to link request and reply messages in an
exchange between two parties. Clause 5.10.1 provides the
specification details. Clause C.3.8 in provides the rationale.
- Content-identifier. as defined in ESS (RFC 2634 [5]) contains an
identifier that may be used later on in the previous content-
reference attribute. Clause 5.10.2 provides the specification
details. Clause C.3.8 in provides the rationale.
- Commitment-type-indication. This attribute is defined by the
present document as a way to indicate the commitment endorsed by
the signer when producing the signature. Clause 5.11.1 provides
the specification details. Clause C.3.2 in provides the
rationale.
- Signer-location. This attribute is defined by the present
document. It allows the signer to indicate the place where he
has purportedly produced the signature. Clause 5.11.2 provides
the specification details. Clause C.3.5 provides the rationale.
- Signer-attributes. This attribute is defined by the present
document. It allows a claimed or certified role to be
incorporated into the signed information. Clause 5.11.3 provides
the specification details. Clause C.3.4 provides the rationale.
- Content-time-stamp. This attribute is defined by the present
document. It allows a time-stamp token of the data to be signed
to be incorporated into the signed information. It provides
proof of the existence of the data before the signature was
created. Clause 5.11.4 provides the specification details.
Clause C.3.6 provides the rationale.
A CAdES-BES form can also incorporate instances of unsigned attributes
as defined in CMS (RFC 3852 [4]) and (RFC 2634 [5]).
- CounterSignature. as defined in CMS (RFC 3852 [4]). It can be
incorporated wherever allowing embedded signatures is a
requirement. Clause 5.9.2 provides the specification details.
Clause C.5 in annex C provides the rationale.
The structure of the CAdES-BES is illustrated in figure 1.
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+------Elect.Signature (CAdES-BES)------+
|+----------------------------------- + |
||+---------+ +----------+ | |
|||Signer's | | Signed | Digital | |
|||Document | |Attributes| Signature | |
||| | | | | |
||+---------+ +----------+ | |
|+------------------------------------+ |
+---------------------------------------+
Figure 1: Illustration of a CAdES-BES
The signer's conformance requirements of a CAdES-BES are defined in
clause 8.1.
NOTE: The CAdES-BES is the minimum format for an electronic signature
to be generated by the signer. On its own, it does not
provide enough information for it to be verified in the longer
term. For example, revocation information issued by the
relevant certificate status information issuer needs to be
available for long term validation (see clause 4.4.2).
The CAdES-BES satisfies the legal requirements for electronic
signatures as defined in the European Directive on electronic
signatures, (see annex C for further discussion on relationship of the
present document to the Directive). It provides basic authentication
and integrity protection.
The semantics of the signed data of a CAdES-BES or its context may
implicitly indicate a signature policy to the verifier. Specification
of the contents of signature policies is outside the scope of the
present document.
Further information on signature policies is provided in TR 102 038
(see informative references), RFC 3125 (see informative references) and
clauses 5.8.1, C.1 and C.3.1 of the present document.
4.3.2 CAdES Explicit Policy Electronic Signatures (CAdES-EPES)
A CAdES Explicit Policy-based Electronic Signature (CAdES-EPES) in
accordance with the present document, extends the definition of an
electronic signature to conform to the identified signature policy.
A CAdES Explicit Policy-based Electronic Signature (CAdES-EPES)
incorporates a signed attribute (signature-policy-identifier)
indicating that a signature policy that is mandatory to use to validate
the signature and specifies explicitly the signature policy that shall
be used. This signed attribute is protected by the signature. The
signature may also have other signed attributes required to conform to
the mandated signature policy.
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Clause 5.7.3 provides the details on the specification of signature-
policy-identifier attribute. Clause C.1 provides a short rationale.
Specification of the contents of signature policies is outside the
scope of the present document.
Further information on signature policies is provided in TR 102 038
(see informative references) and clauses 5.8.1, C.1 and C.3.1 of the
present document.
The structure of the CAdES-EPES is illustrated in figure 2.
+------------- Elect.Signature (CAdES-EPES) ---------------+
||+----------------------------------------------------- + |
|| +---------------------------+ | |
|| +---------+ | +----------+ | | |
|| | | | | | | | |
|| |Signer's | | |Signature | Signed | Digital | |
|| |Document | | |Policy ID | Attributes |Signature| |
|| | | | | | | | |
|| +---------+ | +----------+ | | |
|| +---------------------------+ | |
|+-------------------------------------------------------+ |
| |
+----------------------------------------------------------+
Figure 2: Illustration of a CAdES-EPES
The signer's conformance requirements of CAdES-EPES are defined in
clause 8.2.
4.4 Electronic signature formats with validation data
Validation of an electronic signature in accordance with the present
document requires additional data needed to validate the electronic
signature. This additional data is called validation data; and
includes:
- Public Key Certificates (PKCs);
- revocation status information for each PKC;
- trusted time-stamps applied to the digital signature or a time-
mark shall be available in an audit log;
- when appropriate, the details of a signature policy to be used to
verify the electronic signature.
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The validation data may be collected by the signer and/or the verifier.
When the signature policy id is present, it shall meet the requirements
of the signature policy. Validation data includes CA certificates as
well as revocation status information in the form of Certificate
Revocation Lists (CRLs) or certificate status information (OCSP)
provided by an on-line service. Validation data also includes evidence
that the signature was created before a particular point in time this
may be either a time-stamp token or time-mark.
The present document defines unsigned attributes able to contain
validation data that can be added to CAdES-BES and CAdES-EPES leading
to electronic signature formats that include validation data. Clauses
below summarize these formats and their most relevant characteristics.
4.4.1 Electronic Signature with Time (CAdES-T)
Electronic Signature with Time (CAdES-T) in accordance with the present
document is when there exits trusted time associated with the ES.
The trusted time may be provided by:
- the signature-time-stamp as an unsigned attribute added to the
ES;
- A time mark of the ES provided by a trusted service provider.
The signature-time-stamp attribute contains a time-stamp token of the
electronic signature value. Clause 6.1.1 provides the specification
details. Clause C.4.3 in provides the rationale.
A time-mark provided by a Trusted Service would have similar effect to
the signature-time-stamp attribute but in this case no attribute is
added to the ES as it is the responsibility of the TSP to provide
evidence of a time mark when required to do so. The management of time
marks is outside the scope of the present document.
Trusted time provides the initial steps towards providing long term
validity. Electronic signatures with the time stamp attribute forming
the CAdES-T is illustrated in figure 3.
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+-------------------------------------------------CAdES-T ---------+
|+------ CAdES-BES or CAdES-EPES -------+ |
||+-----------------------------------+ | +----------------------+ |
|||+---------+ +----------+ | | | | |
||||Signer's | | Signed | Digital | | | Signature-time-stamp | |
||||Document | |Attributes| Signature | | | attribute required | |
|||| | | | | | | when using time | |
|||+---------+ +----------+ | | | stamps. | |
||+-----------------------------------+ | | | |
|+--------------------------------------+ | or the BES/EPES | |
| | shall be tme marked | |
| | | |
| | Management and | |
| | provision of time | |
| | mark is the | |
| | responsibility of | |
| | the TSP. | |
| +----------------------+ |
+------------------------------------------------------------------+
Figure 3: Illustration of CAdES-T formats
NOTE A time stamp token is added to the CAdES-BES or CAdES-EPES as
an unsigned attribute.
4.4.2 ES with Complete validation data references (CAdES-C)
Electronic Signature with Complete validation data references (CAdES-C)
in accordance with the present document adds to the CAdES-T the
complete-certificate-references and complete-revocation-references
attributes as defined by the present document. The complete-
certificate-references attribute contain references to all the
certificates present in the certification path used for verifying the
signature. The complete-revocation-references attribute contains
references to the CRLs and/or OCSP responses used for verifying the
signature. Clause 6.2 provides the specification details. Storing the
references allows the values of the certification path and the CRLs or
OCSPs responses to be stored elsewhere, reducing the size of a stored
electronic signature format.
Clauses C.4.1 to C.4.2 provide rationale on the usage of validation
data and when it is suitable to generate the CAdES-C form.
Electronic signatures with the additional validation data forming the
CAdES-C are illustrated in figure 4.
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+------------------------- CAdES-C --------------------------------+
|+----------------------------- CAdES-T ---------+ |
|| +----------+ | +-------------+ |
|| |Timestamp | | | | |
|| |attribute | | | | |
||+- CAdES-BES or CAdES-EPES ------+|over | | | | |
||| ||digital | | | Complete | |
|||+---------++----------+ ||signature | | | certificate | |
||||Signer's || Signed | Digital ||is | | | and | |
||||Document ||Attributes|Signature||mandatory | | | revocation | |
|||| || | ||if is | | | references | |
|||+---------++----------+ ||NOT | | | | |
||+--------------------------------+|timemarked| | | | |
|| +----------+ | | | |
|| | +-------------+ |
|+-----------------------------------------------+ |
| |
+------------------------------------------------------------------+
Figure 4: Illustration of CAdES-C format
NOTE 1: The complete certificate and revocation references are added
to the CAdES-T as an unsigned attribute.
NOTE 2: As a minimum, the signer will provide the CAdES-BES or when
indicating that the signature conforms to an explicit signing
policy the CAdES-EPES.
NOTE 3: To reduce the risk of repudiating signature creation, the
trusted time indication needs to be as close as possible to
the time the signature was created. The signer or a TSP could
provide the CAdES-T, if not the verifier should create the
CAdES-T on first receipt of an electronic signature because
the CAdES-T provides independent evidence of the existence of
the signature prior to the trusted time indication.
NOTE 4: An CAdES-T trusted time indications must be created before a
certificate has been revoked or expired.
NOTE 5: The signer and TSP could provide the CAdES-C, to minimize
this risk and when the signer does not provide the CAdES-C,
the verifier should create the CAdES-C when the required
component of revocation and validation data become available,
this may require a grace period.
NOTE 6: A grace period permits certificate revocation information to
propagate through the revocation processes. This period could
extend from the time an authorized entity requests certificate
revocation, to when the information is available for the
relying to use. In order to make sure that the certificate
was not revoked at the time the signature was time-marked or
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time-stamped, verifiers should wait until the end of the grace
period. A signature policy may define specific values for
grace periods. An illustration of a grace period is provided
in figure 5.
+<--------------Grace Period --------->+
----+-------+-------+--------+---------------------+----------+
^ ^ ^ ^ ^ ^
| | | | | |
| | | | | |
Signature | First | Second |
creation | revocation | revocation |
time | status | status |
| checking | checking |
| | |
Time-stamp Certification Build
or path CAdES-C
time-mark construction
over & verification
signature
Figure 5: Illustration of a grace period
Figure 5: Illustration of a grace period
NOTE 7: CWA 14171 (see informative references) specifies a signature
validation process using CAdES-T, CAdES-C and a grace period.
Annex B provides example validation processes. Clause C.4
provides additional information about applying grace periods
during the validation process.
The verifier's conformance requirements are defined in clause 8.3 for
time stamped CAdES-C and clause 8.4 for time marked CAdES-C. The
present document only defines conformance requirements for the verifier
up to an ES with complete validation data (CAdES-C). This means that
none of the extended and archive forms of Electronic Signature as
defined in clauses 4.4.3 to 4.4.4) need to be implemented to achieve
conformance to the present document.
4.4.3 Extended electronic signature formats
CAdES-C can be extended by adding unsigned attributes to the electronic
signature. The present document defines various unsigned attributes
that are applicable for very long term verification, and for preventing
some disaster situations which are discussed in annex C. Annex B
provides the details of the various extended formats, all the required
unsigned attributes for each type and how they can be used within the
electronic signature validation process. The clauses below give an
overview of the various forms of extended signature formats in the
present document.
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4.4.3.1 EXtended Long Electronic Signature (CAdES-X Long)
Extended Long format (CAdES-X Long) in accordance with the present
document adds to the CAdES-C format the certificate-values and
revocation-values attributes. The first one contains the whole
certificate path required for verifying the signature; the second one
the CRLs and/OCSP responses required for the validation of the
signature. This provides a know repository of certificate and
revocation information required to validate an CAdES-C and prevents
such information getting lost. Clauses 6.3.3 and 6.3.4 give
specification details. Clause B.1.1 gives details on the production of
the format. Clauses C4.1 to C.4.2 provide the rationale.
The structure of the CAdES-X Long format is illustrated in figure 6.
+----------------------- CAdES-X-Long -----------------------------+
|+------------------------------------ CadES-C --+ |
|| +----------+ | +-------------+ |
||+------ CAdES -------------------+|Timestamp | | | | |
||| || over | | | Complete | |
|||+---------++----------+ ||digital | | | certificate | |
||||Signer's || Signed | Digital ||signature | | | and | |
||||Document ||Attributes|Signature|| | | | revocation | |
|||| || | ||Optional | | | data | |
|||+---------++----------+ ||when | | | | |
||+--------------------------------+|timemarked| | | | |
|| +----------+ | | | |
|| +-------------+ | +-------------+ |
|| | Complete | | |
|| | certificate | | |
|| | and | | |
|| | revocation | | |
|| | references | | |
|| +-------------+ | |
|+-----------------------------------------------+ |
| |
+------------------------------------------------------------------+
Figure 6: Illustration of CAdES-X-Long
4.4.3.2 EXtended Electronic Signature with Time Type 1
(CAdES-X Type 1)
Extended format with time type 1 (CAdES-X Type 1) in accordance with
the present document adds to the CAdES-C format the CAdES-C-time-stamp
attribute, whose content is a time-stamp token on the CAdES-C itself.
This provides an integrity and trusted time protection over all the
elements and references. It may protect the certificates, CRLs and
OCSP responses in case of a later compromise of a CA key, CRL key or
OCSP issuer key. Clause 6.3.5 provides the specification details.
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Clause B.1.2 gives details on the production of the time-stamping
process. Clauses C.4.4.1 provides the rationale.
The structure of the CAdES-X Type 1 format is illustrated in figure 7.
+----------------------- CAdES-X-Type 1 -----------------------------+
|+-------------------------------------- CAdES-C --+ |
|| +----------+ | +-------------+ |
||+--------- CAdES ------------------+|Timestamp | | | | |
||| ||over | | | | |
|||+---------++----------++---------+||digital | | | | |
||||Signer's || Signed || Digital |||signature | | | Timestamp | |
||||Document ||Attributes||Signature||| | | | over | |
|||| || || |||Optional | | | CAdES-C | |
|||+---------++----------++---------+||when | | | | |
||+----------------------------------+|timemarked| | | | |
|| +----------+ | | | |
|| +-------------+ | +-------------+ |
|| | Complete | | |
|| | certificate | | |
|| | and | | |
|| | revocation | | |
|| | references | | |
|| +-------------+ | |
|+-------------------------------------------------+ |
| |
+--------------------------------------------------------------------+
Figure 7: Illustration of CAdES-X Type 1
4.4.3.3 EXtended Electronic Signature with Time Type 2
(CAdES-X Type 2)
Extended format with time type 2 (CAdES-X Type 2) in accordance with
the present document adds to the CAdES-C format the CAdES-C-time-
stamped-certs-crls-references attribute, whose content is a time-stamp
token on the certification path and revocation information references.
This provides an integrity and trusted time protection over all the
references.
It may protect the certificates, CRLs and OCSP responses in case of a
later compromise of a CA key, CRL key or OCSP issuer key.
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Both CAdES-X Type 1 and CAdES-X Type 2 counter the same threats and the
usage of one or the other depends on the environment. Clause 6.3.5
provides the specification details. Clause B.1.3 gives details on the
production of the time-stamping process. Clause C.4.4.2 provides the
rationale.
The structure of the CAdES-X Type 2 format is illustrated in figure 8.
+------------------------- CAdES-X-Type 2 ---------------------------+
|+-----------------------------------------CAdES-C --+ |
|| +-----------+| |
||+----- CAdES ------------------------+| Timmestamp|| |
||| || over || |
|||+---------+ +----------+ +---------+|| digital ||+-------------+|
||||Signer's | | Signed | | Digital ||| signature ||| Time-stamp ||
||||Document | |Attributes| |signature||| ||| only over ||
|||| | | | | ||| optional ||| complete ||
|||+---------+ +----------+ +---------+|| when ||| certificate ||
||+------------------------------------+| timemarked||| and ||
|| +-----------+|| revocation ||
|| +-------------+|| references ||
|| | Complete ||+-------------+|
|| | certificate || |
|| | and || |
|| | revocation || |
|| | references || |
|| +-------------+| |
|+---------------------------------------------------+ |
| |
+--------------------------------------------------------------------+
Figure 8: Illustration of CAdES-X Type 2
4.4.3.4 EXtended Long Electronic Signature with Time (CAdES-X Long Type
1 or 2)
Extended Long with Time (CAdES-X Long Type 1 or 2) in accordance with
the present document is a combination of CAdES-X Long and one of the
two former types (CAdES-X Type 1 and CAdES-X Type 2). Clause B.1.4
gives details on the production of the time-stamping process. Clause
C4.8 in annex C provides the rationale.
The structure of the CAdES-X Long Type 1 and CAdES-X Long Type 2.
format is illustrated in figure 9.
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+------------------ CAdES-X Long Type 1 or 2 -----------------------+
| +--------------+|
|+-------------------------------------- CAdES-C --+|+------------+||
|| ||| Timestamp |||
||+------- CAdES --------------------++----------+ ||| over |||
||| ||Timestamp | ||| CAdES-C |||
||| ||over | ||+------------+||
|||+---------++----------++---------+||digital | || OR ||
||||Signer's || Signed || Digital |||signature | ||+------------+||
||||Document ||Attributes||signature||| | ||| Timestamp |||
|||| || || |||Optional | ||| only over |||
|||+---------++----------++---------+||when | ||| complete |||
||+----------------------------------+|timemarked| ||| certificate|||
|| +----------+ ||| and |||
|| ||| Revocation |||
|| +-------------+ ||| References |||
|| | Complete | ||+------------+||
|| | certificate | |+--------------+|
|| | and | | +------------+ |
|| | revocation | | | Complete | |
|| | references | | |certificate | |
|| +-------------+ | | and | |
|+-------------------------------------------------+ |revocation | |
| | value | |
| +------------+ |
+-------------------------------------------------------------------+
Figure 9: Illustration of CAdES-X Long Type 1 and CAdES Long Type 2
4.4.4 Archival Electronic Signature (CAdES-A)
Archival Form (CAdES-A) in accordance with the present document builds
on a CAdES-X Long or a CAdES-X Long Type 1 or 2 by adding one or more
archive-time-stamp attributes. This form is used for archival of long-
term signatures. Successive time-stamps protect the whole material
against vulnerable hashing algorithms or the breaking of the
cryptographic material or algorithms. Clause 6.4 contains the
specification details. Clauses C.4.5 and C.4.8 provide the rationale.
The structure of the CAdES-A form is illustrated in figure 10.
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+---------------------------CAdES-A ---------------------------------+
|+----------------------------------------------------+ |
|| +--------------+| +----------+ |
||+----------------------CAdES-C ----+|+------------+|| | | |
||| +----------+ ||| Timestamp ||| | | |
|||+---- CAdES-BES ----+|Timestamp | ||| over ||| | | |
|||| or CAdeS-EPES || over | ||| CAdES-C ||| | Archive | |
|||| ||digital | ||+------------+|| | | |
|||| ||signature | || or || |Timestamp | |
|||| || | ||+------------+|| | | |
|||| ||Optional | ||| Timestamp ||| | | |
|||| ||when | ||| only over ||| | | |
|||| ||Timemarked| ||| complete ||| | | |
|||+-------------------+| | ||| certificate||| +----------+ |
||| +----------+ ||| and ||| |
||| +-------------+ ||| revocation ||| |
||| | Complete | ||| references ||| |
||| | certificate | ||+------------+|| |
||| | and | |+--------------+| |
||| | revocation | | +------------+ | |
||| | references | | | Complete | | |
||| +-------------+ | |certificate | | |
||| | | and | | |
||+----------------------------------+ |revocation | | |
|| | values | | |
|| +------------+ | |
|+----------------------------------------------------+ |
+--------------------------------------------------------------------+
Figure 10: Illustration of CAdES-A
TABLE NOTE : Timestamps are timestamp token that may themselves
include unsigned attributes required to validate the timestamp
token, such as the complete-certificate-references and
complete-revocation-references attributes as defined by the
present document.
4.5 Arbitration
The CAdES-C may be used for arbitration should there be a dispute
between the signer and verifier, provided that:
- the arbitrator knows where to retrieve the signer's certificate
(if not already present), all the cross-certificates and the
required CRLs, ACRLs or OCSP responses referenced in the CAdES-C;
- when time-stamping in the CAdES-T is being used, the certificate
from the TSU that has issued the time-stamp token in the CAdES-T
format is still within its validity period;
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- when time-stamping in the CAdES-T is being used, the certificate
from the TSU that has issued the time-stamp token in the CAdES-T
format is not revoked at the time of arbitration;
- when time-marking in the CAdES-T is being used, a reliable audit
trail from the Time-Marking Authority is available for
examination regarding the time;
- none of the private keys corresponding to the certificates used
to verify the signature chain have ever been compromised;
- the cryptography used at the time the CAdES-C was built has not
been broken at the time the arbitration is performed;
- If the signature policy can be explicit or implicitly identified
then an arbitrator is able to determine the rules required to
validate the electronic signature.
4.6 Validation process
The Validation Process validates an electronic signature, the output
status of the validation process can be:
- invalid;
- incomplete validation;
- valid.
An Invalid response indicates that either the signature format is
incorrect or that the digital signature value fails verification (e.g.
the integrity check on the digital signature value fails or any of the
certificates on which the digital signature verification depends is
known to be invalid or revoked).
An Incomplete Validation response indicates that the signature
validation status is currently unknown. In the case of incomplete
validation, additional information may be made available to the
application or user, thus allowing them to decide what to do with the
electronic signature. In the case of incomplete validation, the
electronic signature may be checked again at some later time when
additional information becomes available.
NOTE: For example; an incomplete validation may be because all the
required certificates are not available or the grace period is
not completed.
A Valid response indicates that the signature has passed verification
and it complies with the signature validation policy.
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Example validation sequences are illustrated in annex B.
5 Electronic signature attributes
This clause builds upon the existing Cryptographic Message Syntax
(CMS), as defined in RFC 3852 [4], and Enhanced Security Services
(ESS), as defined in RFC 2634 [5]. The overall structure of Electronic
Signature is as defined in CMS. The Electronic Signature (ES) uses
attributes defined in CMS, ESS and the present document. The present
document defines ES attributes which it uses and are not defined
elsewhere.
The mandated set of attributes and the digital signature value is
defined as the minimum Electronic Signature (ES) required by the
present document. A signature policy MAY mandate that other signed
attributes are present.
5.1 General syntax
The general syntax of the ES is as defined in CMS (RFC 3852 [4]).
NOTE: CMS defines content types for id-data, id-signedData, id-
envelopedData, id-digestedData, id-encryptedData, and id-
authenticatedData. Although CMS permits other documents to
define other content types, the ASN.1 type defined should not
be a CHOICE type. The present document does not define other
content types.
5.2 Data content type
The data content type of the ES is as defined in CMS (RFC 3852 [4]).
NOTE: Requirements to identify encoding types within the content when
the ContentType set to id-data are outside the scope of the
present document, see annex F for an example of using MIME to
identify encoding type.
5.3 Signed-data content type
The signed-data content type of the ES is as defined in CMS (RFC 3852
[4]).
To make sure that the verifier uses the right signer's key, the present
document mandates that an unambiguous reference of the signer's
certificate is always included in the Signing Certificate signed
attribute (see clause 5.7.3).
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5.4 SignedData type
The syntax of the SignedData of the ES is as defined in CMS (RFC 3852
[4]).
The fields of type SignedData have the meanings as defined in CMS (RFC
3852 [4]) except that:
- the syntax version number value shall be 3.
The identification of signer's certificate used to create the signature
is always signed (see clause 5.7.3). The validation policy may specify
requirements for the presence of certain certificates.
The degenerate case where there are no signers is not valid in the
present document.
5.5 EncapsulatedContentInfo type
The syntax of the EncapsulatedContentInfo type ES is as defined in CMS
(RFC 3852 [4]).
For the purpose of long term validation as defined by the present
document, it is advisable that either the eContent is present, or the
data which is signed is archived in such as way as to preserve any data
encoding. It is important that the OCTET STRING used to generate the
signature remains the same every time either the verifier or an
arbitrator validates the signature.
NOTE: The eContent is optional in CMS, this allows the signed data
to be encapsulated in the SignData (i.e. Signature + data)
alternatively the signed data may be absent form the SignData
(i.e. Signature only). It is in the case of signature only
that the data which is signed needs to be archived in such as
way as to preserve any data encoding.
The degenerate case where there are no signers is not valid in the
present document.
5.6 SignerInfo type
The syntax of the SignerInfo type ES is as defined in CMS (RFC 3852
[4]).
Per-signer information is represented in the type SignerInfo. In the
case of multiple independent signatures (see clause B.5), there is an
instance of this field for each signer.
The fields of type SignerInfo have the meanings defined in CMS (RFC
3852 [4]) except that the signedAttrs field shall contain the following
attributes:
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- content-type as defined in clause 5.7.1;
- message-digest as defined in clause 5.7.2;
- signing-certificate as defined in clause 5.7.3.
5.6.1 Message digest calculation process
The message digest calculation process is as defined in CMS (RFC 3852
[4]).
5.6.2 Message signature generation process
The input to the message signature generation process is as defined in
CMS (RFC 3852 [4]).
5.6.3 Message signature verification process
The procedures for message signature verification are defined in CMS
(RFC 3852 [4]) and enhanced in the present document.
The input to the signature verification process includes the signer's
public key which SHALL be verified as correct using the signing
certificate reference attribute containing a reference to the signing
certificate.
5.7 Basic ES mandatory present attributes
The following attributes SHALL be present with the signed-data defined
by the present document. The attributes are defined in CMS (RFC 3852
[4]).
5.7.1 Content type
The syntax of the content-type attribute type of the ES is as defined
in CMS (RFC 3852 [4]).
5.7.2 Message digest
The syntax of the message-digest attribute type of the ES is as defined
in CMS (RFC 3852 [4]).
5.7.3 Signing certificate reference attributes
The Signing certificate reference attributes are supported by using
either the ESS signing-certificate attribute or the other-signing-
certificate attribute.
These attributes shall contain a reference to the signer's certificate,
they are designed to prevent the simple substitution and re-issue
attacks and to allow for a restricted set of certificates to be used in
verifying a signature. They have a compact form (much shorter than the
full certificate) that allows to a certificate to be unambiguously
identified.
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One, and only one, of the following alternative attributes SHALL be
present with the signedData defined by the present document.
- The ESS signing-certificate attribute, which is adopted in
existing standards, may be used if the SHA-1 hashing algorithm is
used.
- The other-signing-certificate attribute shall be used when other
hashing algorithms are to be utilized.
The certificate to be used to verify the signature shall be identified
in the sequence (i.e. the certificate from the signer) and the sequence
shall not be empty. The signature validation policy may mandate other
certificates be present that may include all the certificates up to the
point of trust.
5.7.3.1 ESS signing certificate attribute definition
The syntax of the signing-certificate attribute type of the ES is as
defined in Enhanced Security Services (ESS), RFC 2634 [5] and further
qualified in the present document.
The sequence of policy information field is not used in the present
document.
The ESS signing-certificate attribute shall be a signed attribute.
The encoding of the ESSCertID for this certificate shall include the
issuerSerial field.
The issuerAndSerialNumber present in the SignerInfo shall be consistent
with issuerSerial field. The certificate identified shall be used
during the signature verification process. If the hash of the
certificate does not match the certificate used to verify the
signature, the signature shall be considered invalid.
NOTE: Where an attribute certificate is used by the signer to
associate a role, or other attributes of the signer, with the
electronic signature this is placed in the signer-attributes
attribute as defined in clause 5.8.3.
5.7.3.2 Other signing certificate attribute definition
The following attribute is identical to the ESS signing-certificate
defined above except that this attribute can be used with hashing
algorithms other than SHA-1.
This attribute shall be used in the same manner as defined above for
the ESS signing-certificate attribute.
The following object identifier identifies the other-signing-
certificate attribute:
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id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 19 }
The other-signing-certificate attribute value has the ASN.1 syntax
OtherSigningCertificate:
OtherSigningCertificate ::= SEQUENCE {
certs SEQUENCE OF OtherCertID,
policies SEQUENCE OF PolicyInformation OPTIONAL
-- NOT USED IN THE PRESENT DOCUMENT }
OtherCertID ::= SEQUENCE {
otherCertHash OtherHash,
issuerSerial IssuerSerial OPTIONAL }
OtherHash ::= CHOICE {
sha1Hash OtherHashValue, -- This contains a SHA-1 hash
otherHash OtherHashAlgAndValue}
OtherHashValue ::= OCTET STRING
OtherHashAlgAndValue ::= SEQUENCE {
HashAlgorithm AlgorithmIdentifier,
HashValue OtherHashValue }
5.8 Additional mandatory attributes for Explicit Policy-based
Electronic Signatures
5.8.1 Signature policy identifier
he present document mandates that for CAdES-EPES a reference to the
signature policy is included in the signedData. This reference is
explicitly identified. A signature policy defines the rules for
creation and validation of an electronic signature, is included as a
signed attribute with every Explicit Policy-based Electronic Signature.
The signature-policy-identifier shall be a signed attribute.
The following object identifier identifies signature-policy-identifier
attribute:
id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 15 }
signature-policy-identifier attribute values have ASN.1 type
SignaturePolicyIdentifier:
SignaturePolicyIdentifier ::=CHOICE{
signaturePolicyId SignaturePolicyId,
signaturePolicyImplied SignaturePolicyImplied
-- not used in this version}
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SignaturePolicyId ::= SEQUENCE {
sigPolicyId SigPolicyId,
sigPolicyHash SigPolicyHash OPTIONAL,
sigPolicyQualifiers SEQUENCE SIZE (1..MAX) OF
SigPolicyQualifierInfo OPTIONAL}
SignaturePolicyImplied ::= NULL
The sigPolicyId field contains an object-identifier which uniquely
identifies a specific version of the signature policy. The syntax of
this field is as follows:
SigPolicyId ::= OBJECT IDENTIFIER
The sigPolicyHash field optionally contains the identifier of the hash
algorithm and the hash of the value of the signature policy.
If the signature policy is defined using ASN.1, then the hash is
calculated on the value without the outer type and length fields and
the hashing algorithm shall be as specified in the field sigPolicyHash.
If the signature policy is defined using another structure, the type of
structure and the hashing algorithm shall be either specified as part
of the signature policy, or indicated using a signature policy
qualifier.
SigPolicyHash ::= OtherHashAlgAndValue
NOTE: In the previous version of TS 101 733 (i.e. version 1.5.1)
sigPolicyHash was mandatory. Implementations requiring to be
backward compatible with version 1.5.1 and previous versions
of the current document MUST include SigPolicyHash.
A signature policy identifier may be qualified with other information
about the qualifier. The semantics and syntax of the qualifier is as
associated with the object-identifier in the sigPolicyQualifierId
field. The general syntax of this qualifier is as follows:
SigPolicyQualifierInfo ::= SEQUENCE {
sigPolicyQualifierId SigPolicyQualifierId,
sigQualifier ANY DEFINED BY sigPolicyQualifierId }
The present document specifies the following qualifiers:
- spuri: this contains the web URI or URL reference to the
signature policy;
- sp-user-notice: this contains a user notice which should be
displayed whenever the signature is validated.
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sigpolicyQualifierIds defined in the present document
SigPolicyQualifierId ::=
OBJECT IDENTIFIER
id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 1 }
SPuri ::= IA5String
id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 2 }
SPUserNotice ::= SEQUENCE {
noticeRef NoticeReference OPTIONAL,
explicitText DisplayText OPTIONAL}
NoticeReference ::= SEQUENCE {
organization DisplayText,
noticeNumbers SEQUENCE OF INTEGER }
DisplayText ::= CHOICE {
visibleString VisibleString (SIZE (1..200)),
bmpString BMPString (SIZE (1..200)),
utf8String UTF8String (SIZE (1..200)) }
5.9 CMS imported optional attributes
The following attributes MAY be present with the signed-data, the
attributes are defined in CMS (RFC 3852 [4]) and are imported into the
present document. Were appropriated the attributes are qualified and
profiled by the present document.
5.9.1 Signing time
The signing-time attribute specifies the time at which the signer
claims to have performed the signing process.
Signing-time attribute values for ES have the ASN.1 type SigningTime as
defined in CMS (RFC 3852 [4]). This type is further qualified in the
present document.
The present document recommends the use of GeneralizedTime.
5.9.2 Countersignature
The counterSignature attribute values for ES have ASN.1 type
CounterSignature as defined in CMS (RFC 3852 [4]).
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A counterSignature attribute shall be an unsigned attribute.
5.10 ESS imported optional attributes
The following attributes MAY be present with the signed-data defined by
the present document. The attributes are defined in ESS and are
imported into the present document and were appropriate qualified and
profiled by the present document.
5.10.1 Content reference attribute
The content-reference attribute is a link from one SignedData to
another. It may be used to link a reply to the original message to
which it refers, or to incorporate by reference one SignedData into
another. The content-reference attribute shall be a signed attribute.
Content-reference attribute values for ES have ASN.1 type
ContentReference as defined in ESS (RFC 2634 [5]).
The content-reference attribute shall be used as defined in ESS (RFC
2634 [5]) and further qualified in the present document.
5.10.2 Content identifier attribute
The content-identifier attribute provides an identifier for the signed
content for use when reference may be later required to that content,
for example in the content reference attribute in other signed data
sent later. The content-identifier shall be a signed attribute.
content-identifier attribute type values for of the ES have ASN.1 type
ContentIdentifier as defined in ESS (RFC 2634 [5]).
The minimal content-identifier attribute should contain a concatenation
of user-specific identification information (such as a user name or
public keying material identification information), a GeneralizedTime
string, and a random number.
5.10.3 Content hints attribute
The content-hints attribute provides information that describes the
format of the signed content. It may be used by the signer to indicate
to a verifier a precise presentation format of the signed data (e.g.
text, voice, and video). This attribute SHOULD be present when the
signed data is to be presented to human users on verification if the
presentation format is not implicit within the data that has been
signed.
The syntax of the content-hints attribute type of the ES as defined in
ESS (RFC 2634 [5]).
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When used to indicate the precise format of the data to be presented to
the user the following rules apply:
- the contentType indicates the type of the associated content. It
is an object identifier (i.e. a unique string of integers)
assigned by an authority that defines the content type;
- when the contentType is id-data the contentDescription shall
define the presentation format, the format may be defined by MIME
types.
When the format of the content is defined by MIME types the following
rules apply:
- the contentType shall be id-data as defined in CMS (RFC 3852
[4]);
- the contentDescription shall be used to indicate the encoding of
the data in accordance with the rules defined RFC 2045 [6], see
annex F for an example structured contents and MIME.
NOTE 1: id-data OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
rsadsi(113549) pkcs(1) pkcs7(7) 1 }
NOTE 2: contentDescription is optional in ESS (RFC 2634 [5]). It may
be used to complement contentTypes defined elsewhere , such
definitions are outside the scope of the present document.
5.11 Additional optional attributes defined in the present document
This clause defines a number of attributes that may be used to meet
specific requirements.
5.11.1 Commitment type indication attribute
There may be situations where a signer wants to explicitly indicate to
a verifier that by signing the data, it illustrates a type of
commitment on behalf of the signer. The commitment-type-indication
attribute conveys such information.
The commitment-type-indication attribute shall be a signed attribute.
The commitment type may be:
- defined as part of the signature policy, in which case the
commitment type has precise semantics that is defined as part of
the signature policy;
- be a registered type, in which case the commitment type has
precise semantics defined by registration, under the rules of the
registration authority. Such a registration authority may be a
trading association or a legislative authority.
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The signature policy specifies a set of attributes that it
"recognizes". This "recognized" set includes all those commitment
types defined as part of the signature policy as well as any externally
defined commitment types that the policy may choose to recognize. Only
recognized commitment types are allowed in this field.
The following object identifier identifies the commitment-type-
indication attribute:
id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16}
commitment-type-indication attribute values have ASN.1 type
CommitmentTypeIndication.
CommitmentTypeIndication ::= SEQUENCE {
commitmentTypeId CommitmentTypeIdentifier,
commitmentTypeQualifier SEQUENCE SIZE (1..MAX) OF
CommitmentTypeQualifier OPTIONAL}
CommitmentTypeIdentifier ::= OBJECT IDENTIFIER
CommitmentTypeQualifier ::= SEQUENCE {
commitmentTypeIdentifier CommitmentTypeIdentifier,
qualifier ANY DEFINED BY commitmentTypeIdentifier }
The use of any qualifiers to the commitment type is outside the scope
of the present document.
The following generic commitment types are defined in the present
document:
id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 1}
id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 2}
id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 3}
id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 4}
id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 5}
id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 6}
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These generic commitment types have the following meaning:
Proof of origin indicates that the signer recognizes to have created,
approved and sent the message.
Proof of receipt indicates that signer recognizes to have received the
content of the message.
Proof of delivery indicates that the TSP providing that indication has
delivered a message in a local store accessible to the recipient of the
message.
Proof of sender indicates that the entity providing that indication has
sent the message (but not necessarily created it).
Proof of approval indicates that the signer has approved the content of
the message.
Proof of creation indicates that the signer has created the message
(but not necessarily approved, nor sent it).
5.11.2 Signer location attribute
The signer-location attribute specifies a mnemonic for an address
associated with the signer at a particular geographical (e.g. city)
location. The mnemonic is registered in the country in which the
signer is located and is used in the provision of the Public Telegram
Service (according to ITU-T Recommendation F.1 [11]).
The signer-location attribute shall be a signed attribute.
The following object identifier identifies the signer-location
attribute:
id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 17}
Signer-location attribute values have ASN.1 type SignerLocation:
SignerLocation ::= SEQUENCE { -- at least one of the following shall be
present
countryName [0] DirectoryString OPTIONAL,
-- As used to name a Country in X.500
localityName [1] DirectoryString OPTIONAL,
-- As used to name a locality in X.500
postalAdddress [2] PostalAddress OPTIONAL }
PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString
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5.11.3 Signer attributes attribute
The signer-attributes attribute specifies additional attributes of the
signer (e.g. role).
It may be either:
- claimed attributes of the signer;
- certified attributes of the signer.
The signer-attributes attribute shall be a signed attribute.
The following object identifier identifies the signer-attribute
attribute:
id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18}
signer-attributes values have ASN.1 type SignerAttribute:
SignerAttribute ::= SEQUENCE OF CHOICE {
ClaimedAttributes [0] ClaimedAttributes,
certifiedAttributes [1] CertifiedAttributes }
ClaimedAttributes ::= SEQUENCE OF Attribute
CertifiedAttributes ::= AttributeCertificate
-- as defined in RFC 3281 : see clause 4.1.
NOTE 1: Only a single signer-attributes can be used
NOTE 2: The claimedAttributes and certifiedAttributes fields are as
defined in ITU-T Recommendations X.501 [9] and X.509 [1].
5.11.4 Content time-stamp
The content-time-stamp attribute is an attribute which is the time-
stamp token of the signed data content before it is signed.
The content-time-stamp attribute shall be a signed attribute.
The following object identifier identifies the content-time-stamp
attribute:
id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 20}
Content-time-stamp attribute values have ASN.1 type ContentTimestamp:
ContentTimestamp::= TimeStampToken
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The value of messageImprint of TimeStampToken (as described in RFC 3161
[7]) shall be a hash of the value of eContent field within
encapContentInfo in the signedData.
For further information and definition of TimeStampToken see
clause 7.4.
NOTE: Content-time-stamp indicates that the signed information was
formed before the date included in the Content-time-stamp.
5.12 Support for multiple signatures
5.12.1 Independent signatures
Multiple independent signatures (see clause B.5) are supported by
independent SignerInfo from each signer.
Each SignerInfo shall include all the attributes required under the
present document and shall be processed independently by the verifier.
5.12.2 Embedded signatures
Multiple embedded signatures (see clause C.5) are supported using the
countersignature unsigned attribute (see clause 7.1). Each counter
signature is carried in Countersignature held as an unsigned attribute
to the SignerInfo to which the counter-signature is applied.
6 Additional Electronic Signature validation attributes
This clause specifies attributes that contain different types of
validation data. These attributes build on the electronic signature
specified in clause 5. This includes:
- Signature-time-stamp applied to the electronic signature value or
a Time-Mark in an audit trail. This is defined as the Electronic
Signature with Time (CAdES-T);
- complete validation data references which comprises the time-
stamp of the signature value (CAdES-T), plus references to all
the certificates (complete-certificate-references) and revocation
(complete-revocation-references) information used for full
validation of the electronic signature. This is defined as the
Electronic Signature with Complete data references (CAdES-C).
NOTE 1: Formats for CAdES-T are illustrated in clause 4.4 and the
attribute are defined in clause 6.1.1.
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NOTE 2: Formats for CAdES-C are illustrated in clause 4.4. The
required attributes for the CAdES-C signature format are
defined in clause 6.2.1 to 6.2.2, optional attributes are
defined in clauses 6.2.3 and 6.2.4.
In addition the following optional eXtended forms of validation data
are also defined, see annex B for an overview the eXtended forms of
validation data:
- CAdES-X with time stamp: there are two types of time-stamp used
in extended validation data defined by the present document:
- Type 1(CAdES-X Type 1): comprises a time-stamp over the ES
with complete validation data (CAdES-C);
- Type 2 (CAdES-X Type2): comprises a time-stamp over the
certification path references and the revocation information
references used to support the CAdES-C.
NOTE 3: Formats for CAdES-X Type 1 and CAdES-X Type 2 are illustrated
in clauses B.1.2 and B.1.3 respectively.
- CAdES-X Long :comprises the complete validation data references
(CAdES-C) plus the actual values of all the certificates and
revocation information used in the CAdES-C.
NOTE 4: Formats for CAdES-X Long are illustrated in clause B.1.1.
- CAdES-X Long Type 1 or CAdES-X Long Type 2: comprises an X-Time-
Stamp (Type 1 or Type 2) plus the actual values of all the
certificates and revocation information used in the CAdES-C as
per CAdES-X Long.
This clause also specifies the data structures used in Archive
validation data format (CAdES-A)of eXtended forms:
- Archive form of electronic signature (CAdES-A) comprises the
complete validation data references (CAdES-C), the certificate
and revocation values (as in a CAdES-X Long ), if present any
existing extended electronic signature timestamps (CAdES-X Type 1
or CAdES-X Type 2), plus the signed user data and an additional
archive time-stamp applied over all that data. An archive time-
stamp may be repeatedly applied after long periods to maintain
validity when electronic signature and time-stamping algorithms
weaken.
The additional data required to create the forms of electronic
signature identified above is carried as unsigned attributes associated
with an individual signature by being placed in the unsignedAttrs field
of SignerInfo . Thus all the attributes defined in clause 6 are
unsigned attributes.
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NOTE 5: Where multiple signatures are to be supported, as described
in clause 5.12, each signature has a separate SignerInfo.
Thus, each signature requires its own unsigned attribute
values to create CAdES-T, CAdES-C, etc.
NOTE 6: the optional attributes of the extended validation data are
defined in clauses 6.3 and 6.4.
6.1 Electronic Signature Time-stamped (CAdES-T)
An Electronic Signature with time-stamp is an electronic signature for
which part, but not all, of the additional data required for validation
is available (i.e. some certificates and revocation information are
available but not all).
The minimum structure time-stamp validation data is:
- the Signature Time-stamp Attribute as defined in clause 6.1.1
over the ES signature value.
6.1.1 Signature time- stamp attribute definition
The signature-time-stamp attribute is a TimeStampToken computed on the
signature value for a specific signer. It is an unsigned attribute.
Several instances of this attribute may occur with an electronic
signature, from different TSAs.
The following object identifier identifies the signature-time-stamp
attribute:
id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 14}
The signature-time-stamp attribute value has ASN.1 type
SignatureTimeStampToken:
SignatureTimeStampToken ::= TimeStampToken
The value of messageImprint field within TimeStampToken shall be a hash
of the value of the signature field within SignerInfo for the
signedData being time-stamped.
For further information and definition of TimeStampToken see
clause 7.4.
NOTE 1: In the case of multiple signatures it is possible to have a
TimeStampToken computed for each and all signers, or
TimeStampToken computed on one signer's signature and no
TimeStampToken on another signer's signature.
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NOTE 2: In the case of multiple signatures, several TSTs , issued by
different TSAs, may be present within the same signerInfo (see
RFC 3852 [4]).
6.2 Complete validation reference data (CAdES-C)
An electronic signature with complete validation data references
(CAdES-C) is an Electronic Signature for which all the additional data
required for validation (i.e. all certificates and revocation
information) is available. This form is built on the CAdES-T form
defined above.
As a minimum the complete validation data shall include the following:
- a time, which shall either be a signature-timestamp attribute, as
defined in clause 6.1.1, or a time mark operated by a Time-
Marking Authority;
- complete-certificate-references, as defined in clause 6.2.1;
- complete-revocation-references , as defined in clause 6.2.2.
6.2.1 Complete certificate references attribute definition
The complete-certificate-references attribute is an unsigned attribute.
It references the full set of CA certificates that have been used to
validate an ES with Complete validation data up to (but not including)
the signer's certificate. Only a single instance of this attribute
shall occur with an electronic signature.
NOTE 1: The signer's certificate is referenced in the signing
certificate attribute (see clause 5.7.3).
id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21}
The complete-certificate-references attribute value has the ASN.1
syntax CompleteCertificateRefs.
CompleteCertificateRefs ::= SEQUENCE OF OtherCertID
OtherCertID is defined in clause 5.7.3.2.
The IssuerSerial that shall be present in OtherCertID. The certHash
shall match the hash of the certificate referenced.
NOTE 2: Copies of the certificate values may be held using the
certificate-values attribute defined in clause 6.3.3.
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This attribute MAY include references to the certification
chain for any TSUs that provides time-stamp tokens. In this
case the unsigned attribute shall be added to the signData of
the relevant times tamp token as an unsignedAttrs in the
signerInfos field.
6.2.2 Complete Revocation References attribute definition
The complete-revocation-references attribute is an unsigned attribute.
Only a single instance of this attribute shall occur with an electronic
signature. It references the full set of the CRL, ACRL or OCSP
responses that have been used in the validation of the signer and CA
certificates used in ES with Complete validation data.
This attribute can be used to illustrate that the verifies has taken
due diligence of the available revocation information and then to be
able to retrieve that information when stored elsewhere.
The following object identifier identifies the complete-revocation-
references attribute:
id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 22}
The complete-revocation-references attribute value has the ASN.1 syntax
CompleteRevocationRefs
CompleteRevocationRefs ::= SEQUENCE OF CrlOcspRef
CrlOcspRef ::= SEQUENCE {
Crlids [0] CRLListID OPTIONAL,
Ocspids [1] OcspListID OPTIONAL,
OtherRev [2] OtherRevRefs OPTIONAL
}
CompleteRevocationRefs shall contain one CrlOcspRef for the signing-
certificate, followed by one for each OtherCertID in the
CompleteCertificateRefs attribute. The second and subsequent
CrlOcspRef fields shall be in the same order as the OtherCertID to
which they relate. At least one of CRLListID or OcspListID or
OtherRevRefs should be present for all but the "trusted" CA of the
certificate path.
CRLListID ::= SEQUENCE {
crls SEQUENCE OF CrlValidatedID}
CrlValidatedID ::= SEQUENCE {
crlHash OtherHash,
crlIdentifier CrlIdentifier OPTIONAL}
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CrlIdentifier ::= SEQUENCE {
crlissuer Name,
crlIssuedTime UTCTime,
crlNumber INTEGER OPTIONAL
}
OcspListID ::= SEQUENCE {
ocspResponses SEQUENCE OF OcspResponsesID}
OcspResponsesID ::= SEQUENCE {
ocspIdentifier OcspIdentifier,
ocspRepHash OtherHash OPTIONAL
}
OcspIdentifier ::= SEQUENCE {
OcspResponderID ResponderID, -- As in OCSP response data
ProducedAt GeneralizedTime -- As in OCSP response data
}
When creating a crlValidatedID, the crlHash is computed over the entire
DER encoded CRL including the signature. The crlIdentifier would
normally be present unless the CRL can be inferred from other
information.
The crlIdentifier is to identify the CRL using the issuer name and the
CRL issued time, which shall correspond to the time thisUpdate
contained in the issued CRL, and if present, the crlNumber. The
crlListID attribute is an unsigned attribute. In the case that the
identified CRL is a Delta CRL then references to the set of CRLs to
provide a complete revocation list shall be included.
The OcspIdentifier is to identify the OCSP response using the issuer
name and the time of issue of the OCSP response which shall correspond
to the time producedAt contained in the issued OCSP response. Since it
may be needed to make the difference between two OCSP responses
received within the same second, then the hash of the response
contained in the OcspResponsesID may be needed to solve the ambiguity.
NOTE: Copies of the CRL and OCSP responses values may be held using
the revocation-values attribute defined in clause 6.3.4.
OtherRevRefs ::= SEQUENCE {
OtherRevRefType OtherRevRefType,
OtherRevRefs ANY DEFINED BY otherRevRefType
}
OtherRevRefType ::= OBJECT IDENTIFIER
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The syntax and semantics of other revocation references is outside the
scope of the present document. The definition of the syntax of the
other form of revocation information is as identified by
OtherRevRefType.
This attribute MAY include the references to the full set of the CRL,
ACRL or OCSP responses that have been used to verify the certification
chain for any TSUs that provides time-stamp tokens. In this case the
unsigned attribute shall be added to the signData of the relevant
timestamp token as an unsignedAttrs in the signerInfos field.
6.2.3 Attribute certificate references attribute definition
This attribute is only used when an user attribute certificate is
present in the electronic signature.
The attribute-certificate-references attribute is an unsigned
attribute. It references the full set of AA certificates that have
been used to validate the attribute certificate. Only a single
instance of this attribute shall occur with an electronic signature.
id-aa-ets-attrCertificateRefs OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 44}
The attribute-certificate-references attribute value has the ASN.1
syntax AttributeCertificateRefs.
AttributeCertificateRefs ::= SEQUENCE OF OtherCertID
OtherCertID is defined in clause 5.8.2.
NOTE: Copies of the certificate values may be held using the
certificate-values attribute defined in clause 6.3.3.
6.2.4 Attribute revocation references attribute definition
This attribute is only used when a user attribute certificate is
present in the electronic signature and when that attribute certificate
can be revoked.
The attribute-revocation-references attribute is an unsigned attribute.
Only a single instance of this attribute shall occur with an electronic
signature. It references the full set of the ACRL or OCSP responses
that have been used in the validation of the attribute certificate.
This attribute can be used to illustrate that the verifier has taken
due diligence of the available revocation information.
The following object identifier identifies the attribute-revocation-
references attribute:
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id-aa-ets-attrRevocationRefs OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 45}
The attribute-revocation-references attribute value has the ASN.1
syntax AttributeRevocationRefs.
AttributeRevocationRefs ::= SEQUENCE OF CrlOcspRef
6.3 Extended validation data (CAdES-X)
This clause specifies a number of optional attributes that are used by
extended forms of electronic signatures (see annex B for an overview
these forms of validation data).
6.3.1 Time-stamped validation data (CAdES-X Type 1 or Type 2)
The extended validation data MAY include one of the following
additional attributes, forming a CAdES-X Time-Stamp validation data
(CAdES-X Type 1 or CAdES-X Type 2), to provide additional protection
against later CA compromise and provide integrity of the validation
data used:
- CAdES-C Time-stamp, as defined in clause 6.3.5 (CAdES-X Type 1);
or
- Time-Stamped Certificates and CRLs references, as defined in
clause 6.3.6 (CAdES-X Type 2).
6.3.2 Long validation data (CAdES-X Long, CAdES-X Long Type 1 or 2)
The extended validation data MAY also include the following additional
information, forming a CAdES-X Long, for use if later validation
processes may not have access to this information:
- certificate-values as defined in clause 6.3.3;
- revocation-values as defined in clause 6.3.4.
The extended validation data MAY in addition to certificate-values and
revocation-values as defined in clauses 6.3.3 and 6.3.4 include one of
the following additional attributes, forming an CAdES-X Long Type 1 or
CAdES-X Long Type 2.
- CAdES-C Time-stamp, as defined in clause 6.3.3 (CAdES-X long Type
1); or
- Time-Stamped Certificates and CRLs references, as defined in
clause 6.3.4 (CAdES-X Long Type 2).
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The CAdES-X Long Type 1 or CAdES-X Long Type 2 provide additional
protection against later CA compromise and provide integrity of the
validation data used.
NOTE 1: The CAdES-X Long provides long term proof of a valid
electronic signature as long as the CAs are trusted such that
these keys cannot be compromised or the cryptography used
broken.
NOTE 2: As long as the time stamp data remains valid, the CAdES-X
Long Type 1 and the CAdES-X Long Type 2 provides the following
important property for long standing signatures; that having
been found once to be valid, it shall continue to be so months
or years later, long after the validity period of the
certificates have expired, or after the user key has been
compromised.
6.3.3 Certificate values attribute definition
This attribute MAY be used to contain the certificate information
required for the following forms of eXtended Electronic Signature:
CAdES-X Long , ES X-Long Type 1 and CAdES-X Long Type 2, see clause
B.1.1 for an illustration of this form of electronic signature.
The certificate-values attribute is an unsigned attribute. Only a
single instance of this attribute shall occur with an electronic
signature. It holds the values of certificates referenced in the
complete-certificate-references attribute.
NOTE: If an attribute certificate is used, it is not provided in this
structure but shall be provided by the signer as a signer-
attributes attribute (see clause 5.11.3).
The following object identifier identifies the certificate-values
attribute:
id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23}
The certificate-values attribute value has the ASN.1 syntax
CertificateValues
CertificateValues ::= SEQUENCE OF Certificate
Certificate is defined in clause 7.1 (which is as defined in ITU-T
Recommendation X.509 [1]).
This attribute MAY include the certification information for any TSUs
that have provided the time-stamp tokens if these certificates are not
already included in the TSTs as part of the TSUs signatures. In this
case the unsigned attribute shall be added to the signData of the
relevant timestamp token.
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6.3.4 Revocation values attribute definition
This attribute is used to contain the revocation information required
for the following forms of eXtended Electronic Signature: CAdES-X Long,
ES X-Long Type 1 and CAdES-X Long Type 2, see clause B.1.1 for an
illustration of this form of electronic signature.
The revocation-values attribute is an unsigned attribute. Only a
single instance of this attribute shall occur with an electronic
signature. It holds the values of CRLs and OCSP referenced in the
complete-revocation-references attribute.
The following object identifier identifies the revocation-values
attribute:
id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 24}
The revocation-values attribute value has the ASN.1 syntax
RevocationValues
RevocationValues ::= SEQUENCE {
crlVals [0] SEQUENCE OF CertificateList OPTIONAL,
ocspVals [1] SEQUENCE OF BasicOCSPResponse OPTIONAL,
otherRevVals [2] OtherRevVals OPTIONAL}
OtherRevVals ::= SEQUENCE {
OtherRevValType OtherRevValType,
OtherRevVals ANY DEFINED BY OtherRevValType
}
OtherRevValType ::= OBJECT IDENTIFIER
The syntax and semantics of the other revocation values (OtherRevVals)
is outside the scope of the present document. The definition of the
syntax of the other form of revocation information is as identified by
OtherRevRefType.
CertificateList is defined in clause 7.2 (which as defined in ITU-T
Recommendation X.509 [1]).
BasicOCSPResponse is defined in clause 7.3 (which as defined in RFC
2560 [3]).
This attribute MAY include the values of revocation data including CRLs
and OCSP for any TSUs that have provided the time-stamp tokens if these
certificates are not already included in the TSTs as part of the TSUs
signatures. In this case the unsigned attribute shall be added to the
signData of the relevant timestamp token.
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6.3.5 CAdES-C time-stamp attribute definition
This attribute is used to protect against CA key compromise.
This attribute is used for the time stamping the complete electronic
signature (CAdES-C). It is used in the following forms of eXtended
Electronic Signature; CAdES-X Type 1 and CAdES-X Long Type 1, see
clause B.1.2 for an illustration of this form of electronic signature.
The CAdES-C-timestamp attribute is an unsigned attribute. It is a
time-stamp token of the hash of the electronic signature and the
complete validation data (CAdES-C). It is a special purpose
TimeStampToken Attribute which time-stamps the CAdES-C. Several
instances of this attribute may occur with an electronic signature from
different TSAs.
The following object identifier identifies the CAdES-C-Timestamp
attribute:
id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 25}
The CAdES-C-timestamp attribute value has the ASN.1 syntax
ESCTimeStampToken.
ESCTimeStampToken ::= TimeStampToken
The value of messageImprint field within TimeStampToken shall be a hash
of the concatenated values (without the type or length encoding for
that value) of the following data objects:
- OCTETSTRING of the SignatureValue field within SignerInfo;
- signature-time-stamp; or a time mark operated by a Time-Marking
Authority;
- complete-certificate-references s attribute;
- complete-revocation-references attribute.
For further information and definition of the TimeStampToken see
clause 7.4.
6.3.6 Time-stamped certificates and crls references attribute
definition
This attribute is used to protect against CA key compromise.
This attribute is used for the time stamping certificate and revocation
references. It is used in the following forms of eXtended Electronic
Signature; CAdES-X Type 2 and CAdES-X Long Type 2, see clause B.1.3 for
an illustration of this form of electronic signature.
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A time-stamped-certs-crls-references attribute is an unsigned
attribute. It is a time-stamp token issued for a list of referenced
certificates and OCSP responses/CRLs to protect against certain CA
compromises. Its syntax is as follows:
The following object identifier identifies the time-stamped-certs-crls-
references attribute:
id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::= { iso(1) member
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 26}
The attribute value has the ASN.1 syntax TimestampedCertsCRLs.
TimestampedCertsCRLs ::= TimeStampToken
The value of messageImprint field within TimeStampToken shall be a hash
of the concatenated values (without the type or length encoding for
that value) of the following data objects as present in the ES with
Complete validation data:
- complete-certificate-references attribute;
- complete-revocation-references attribute.
6.4 Archive validation data
Where an electronic signature is required to last for a very long time,
and a the time-stamp token on an electronic signature is in danger of
being invalidated due to algorithm weakness or limits in the validity
period of the TSA certificate, then it may be required to time-stamp
the electronic signature several times. When this is required an
archive time-stamp attribute may be required for the archive form of
electronic signature (CAdES-A). This archive time-stamp attribute may
be repeatedly applied over a period of time.
6.4.1 Archive time-stamp attribute definition
The archive-time-stamp attribute is a time-stamp token of many of the
elements of the signedData in the electronic signature. If the
certificate-values and revocation-values attributes are not present in
the CAdES-BES or CAdES-EPES, then they shall be added to the electronic
signature prior to computing the archive time-stamp token. The
archive-time-stamp attribute is an unsigned attribute. Several
instances of this attribute may occur with an electronic signature both
over time and from different TSUs.
The following object identifier identifies the nested archive-time-
stamp attribute:
id-aa-ets-archiveTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 27}
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Archive-time-stamp attribute values have the ASN.1 syntax
ArchiveTimeStampToken
ArchiveTimeStampToken ::= TimeStampToken
The value of messageImprint field within TimeStampToken shall be a hash
of the concatenation of:
- The encapContentInfo element of the SignedData sequence;
- When present, the Certificates and crls elements of the
SignedData sequence;
- Together with all data elements in the SignerInfo sequence
including all signed and unsigned attributes.
NOTE 1: The SignedData definition is the following:
SignedData ::= SEQUENCE {
version CMSVersion,
digestAlgorithms DigestAlgorithmIdentifiers,
encapContentInfo EncapsulatedContentInfo,
certificates [0] IMPLICIT CertificateSet OPTIONAL,
crls [1] IMPLICIT CertificateRevocationLists OPTIONAL,
signerInfos SignerInfos }
NOTE 2: SignerInfo definition is as follows:
SignerInfo ::= SEQUENCE {
version CMSVersion,
sid SignerIdentifier,
digestAlgorithm DigestAlgorithmIdentifier,
signedAttrs [0] IMPLICIT SignedAttributes OPTIONAL,
signatureAlgorithm SignatureAlgorithmIdentifier,
signature SignatureValue,
unsignedAttrs [1] IMPLICIT UnsignedAttributes OPTIONAL }
Further information and definition of TimeStampToken see clause 7.4.
The timestamp should be created using stronger algorithms (or longer
key lengths) than in the original electronic signatures and weak
algorithm (key length) timestamps.
NOTE 3: This form of ES also provides protection against a TSP key
Compromise.
The ArchiveTimeStamp will be added as an unsigned attribute in the
SignerInfo sequence. For the validation of one ArchiveTimeStamp the
data elements of the SignerInfo must be concatenated excluding all
later ArchivTimeStampToken attributes.
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Certificates and revocation information required to validate the
ArchiveTimeStampshall be provided by one of the following methods:
- The TSU provides the information in the SignedData of the
timestamp token;
- Adding the complete-certificate-references attribute and the
complete-revocation-references attribute of the TSP as an
unsigned attribute within TimeStampToken, when the required
information is store elsewhere;
- Adding the certificate-values attribute and the revocation-values
attribute of the TSP as an unsigned attribute within
TimeStampToken, when the required information is store elsewhere.
7 Other standard data structures
7.1 Public-key certificate format
The X.509 v3 certificate basis syntax is defined in ITU-T
Recommendation X.509 [1]. A profile of the X.509 v3 certificate is
defined in RFC 3280 [2], which is being revised. The reader should
consult the latest version of this RFC or any RFC that makes it
obsolete.
7.2 Certificate revocation list format
The X.509 v2 CRL syntax is defined in ITU-T Recommendation X.509 [1].
A profile of the X.509 v2 CRL is defined in RFC 3280 [2], which is
being revised.
7.3 OCSP response format
The format of an OCSP token is defined in RFC 2560 [3].
7.4 Time-stamp token format
The format of a TimeStampToken type is defined in RFC 3161 [7] and TS
101 861 (see informative references).
7.5 Name and attribute formats
The syntax of the naming and other attributes is defined in ITU-T
Recommendation X.509 [1].
The name used by the signer, held as the subject in the signer's
certificate, shall be allocated and verified on registration with the
Certification Authority, either directly or indirectly through a
Registration Authority, before being issued with a Certificate.
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The present document places no restrictions on the form of the name.
The subject's name may be a distinguished name, as defined in ITU-T
Recommendation X.500 [12], held in the subject field of the
certificate, or any other name form held in the subjectAltName
certificate extension field as defined in ITU-T Recommendation X.509
[1]. In the case that the subject has no distinguished name, the
subject name can be an empty sequence and the subjectAltName extension
shall be critical.
All TSP name forms (Certification Authorities, Attribute Authorities
and Time Stamping Authorities) shall be in the form of a distinguished
name held in the subject field of the certificate.
The TSP name form shall include identifiers for the organization
providing the service and the legal jurisdiction (e.g. country) under
which it operates.
Where a signer signs as an individual but wishes to also identify
him/herself as acting on behalf of an organization, it may be necessary
to provide two independent forms of identification. The first
identity, with is directly associated with the signing key identifies
him/her as an individual. The second, which is managed independently,
identifies that person acting as part of the organization, possibly
with a given role.
In this case one of the two identities is carried in the
subject/subjectAltName field of the signer's certificate as described
above.
The present document does not specify the format of signer's attribute
that may be included in public key certificates.
NOTE : Signer's attribute may be supported by using a claimed role in
the CMS signed attributes field or by placing an attribute
certificate containing a certified role in the CMS signed
attributes field, see clause 7.6.
7.6 Attribute certificate
The syntax of the AttributeCertificate type is defined in RFC 3281 [13].
8. Conformance requirements
The present document defines conformance requirements for the
generation of two forms of basic electronic signature, one of the two
forms must be implemented.
The present document defines conformance requirements for the
verification of two forms of basic electronic signature, one of the two
forms must be implemented.
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The present document only defines conformance requirements up to an ES
with Complete validation data (CAdES-C). This means that none of the
extended and archive forms of Electronic Signature (CAdES-X, CAdES-A)
need to be implemented to get conformance to the present document.
On verification the inclusion of optional signed and unsigned
attributes must be supported only to the extended that the signature is
verifiable. The semantics of optional attributes may be unsupported,
unless specified otherwise by a signature policy.
8.1 CAdES-Basic Electronic Signature (CAdES-BES)
A system supporting CAdES-BES signers according to the present document
shall, at a minimum, support generation of an electronic signature
consisting of the following components:
- The general CMS syntax and content type as defined in RFC 3852
[4] (see clauses 5.1 and 5.2);
- CMS SignedData as defined in RFC 3852 [4] with version set to 3
and at least one SignerInfo shall be present (see clauses 5.3 to
5.6);
- The following CMS attributes as defined in RFC 3852 [4]:
- content-type; this shall always be present (see clause 5.7.1);
- message-digest; this shall always be present (see
clause 5.7.2).
- One of following attributes as defined in the present document:
- signing-certificate: as defined in clause 5.7.3.1;
- Other-Signing-Certificate as defined in clause 5.7.3.2.
8.2 CAdES-Explicit Policy-based Electronic Signature
A system supporting Policy-based signers according to the present
document shall, at a minimum, support generation of an electronic
signature consisting of the previous components defined for the basic
signer, plus:
- The following attributes as defined in clause 5.9:
- signature-policy-identifier; this shall always be present (see
clause 5.8.1).
8.3 Verification using time-stamping
A system supporting verifiers according to the present document with
time-stamping facilities shall, at a minimum, support:
- verification of the mandated components of an electronic
signature, as defined in clause 8.1.
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- signature-time-stamp attribute, as defined in clause 6.1.1.
- complete-certificate-references, attribute as defined in
clause 6.2.1.
- complete-revocation-references attribute, as defined in
clause 6.2.2.
- Public Key Certificates, as defined in ITU-T Recommendation X.509
[1] (see clause 8.1).
- either of:
- Certificate Revocation Lists. as defined in ITU-T
Recommendation X.509 [1] (see clause 8.2); or
- on-line Certificate Status Protocol, as defined in RFC 2560
[3] (see clause 8.3).
8.4 Verification using secure records
A system supporting verifiers according to the present document shall,
at a minimum, support:
- verification of the mandated components of an electronic
signature, as defined in clause 8.1;
- complete-certificate-references attribute, as defined in
clause 6.2.1;
- complete-revocation-references attribute, as defined in
clause 6.2.2;
- a record must be maintained and cannot be undetectable modified,
of the electronic signature and the time when the signature was
first validated using the referenced certificates and revocation
information;
- Public Key Certificates, as defined in ITU-T Recommendation X.509
[1] (see clause 8.1);
- either of:
- Certificate Revocation Lists. as defined in ITU-T
Recommendation X.509 [1] (see clause 8.2); or
- on-line Certificate Status Protocol, as defined in RFC 2560
[3] (see clause 8.3).
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9. Security considerations
9.1 Protection of private key
The security of the electronic signature mechanism defined in the
present document depends on the privacy of the signer's private key.
Implementations should take steps to ensure that private keys cannot be
compromised.
9.2 Choice of algorithms
Implementers should be aware that cryptographic algorithms become
weaker with time. As new cryptoanalysis techniques are developed and
computing performance improves, the work factor to break a particular
cryptographic algorithm will reduce. Therefore, cryptographic
algorithm implementations should be modular allowing new algorithms to
be readily inserted. That is, implementers should be prepared for the
set of mandatory to implement algorithms to change over time.
10. IANA Considerations
Not applicable
11. References
11.1 Normative references
[1] ITU-T Recommendation X.509 (2000)/ISO/IEC 9594-8 (2001):
"Information technology - Open Systems Interconnection -
The Directory: Authentication framework".
[2] IETF RFC 3280 (2002): "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile".
[3] IETF RFC 2560 (1999): "X.509 Internet Public Key
Infrastructure Online Certificate Status Protocol - OCSP".
[4] IETF RFC 3852 (2004): "Cryptographic Message Syntax (CMS)".
[5] IETF RFC 2634 (1999): "Enhanced Security Services for
S/MIME".
[6] IETF RFC 2045 (1996): "Multipurpose Internet Mail Extensions
(MIME) Part One: Format of Internet Message Bodies".
[7] IETF RFC 3161 (2001): "Internet X.509 Public Key
Infrastructure Time-Stamp Protocol (TSP)".
[8] ITU-T Recommendation X.680 (1997): "Information technology -
Abstract Syntax Notation One (ASN.1): Specification of basic
notation".
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[9] ITU-T Recommendation X.501 (2000)/ISO/IEC 9594-1 (2001):
"Information technology - Open Systems Interconnection -
Directory models ".
[10] IETF RFC 3370 (2002): "Cryptographic Message Syntax (CMS)
Algorithms".
[11] ITU-T Recommendation F.1: "Operational provisions for the
international public telegram service".
[12] ITU-T Recommendation X.500: "Information technology - Open
Systems Interconnection - The Directory: Overview of
concepts, models and services".
[13] IETF RFC 3281 (2002): "An Internet Attribute Certificate
Profile for Authorization".
[14] ITU-T Recommendation X.208 (1988): "Specification of Abstract
Syntax Notation One (ASN.1)".
Referenced documents hereabove which are not found to be publicly
available in the expected location might be found at
http://docbox.etsi.org/Reference.
[STDWORDS] IETF RFC 2119 Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC 2
11.2 Informative references
Directive 1999/93/EC of the European Parliament and of the Council
of 13 December 1999 on a Community framework for electronic
signatures.
ETSI Standard TS 101 733 V.1.6.3 (2005-06) Electronic Signature
Formats. Note: copies of ETSI TS 101 733 can be freely downloaded
from the ETSI web site www.etsi.org.
IETF RFC 2246 (1999): "The TLS Protocol Version 1.0".
IETF RFC 2437 (1998): "PKCS #1: RSA Cryptography Specifications
Version 2.0".
IETF RFC 2479 (1998): "Independent Data Unit Protection Generic
Security Service Application Program Interface (IDUP-GSS-API)".
IETF RFC 2510 (1999): "Internet X.509 Public Key Infrastructure
Certificate Management Protocols".
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IETF RFC 2587 (1999): "Internet X.509 Public Key Infrastructure
LDAPv2 Schema".
IETF RFC 3125 (2000): "Electronic Signature Policies".
IETF RFC 2559 (2003): "Internet X.509 Public Key Infrastructure
Operational Protocols - LDAPv2".
ETSI TS 101 861: "Time stamping profile".
ETSI TS 101 903: "XML Advanced Electronic Signatures (XAdES)".
ETSI TS 102 023: "Electronic Signatures and Infrastructures (ESI);
Policy requirements for time-stamping authorities".
ETSI TS 102 038: "Electronic Signatures and Infrastructures (ESI);
XML format for signature policies".
ETSI TR 102 272. "Electronic Signatures and Infrastructures (ESI);
ASN.1 format for signature policies".
ISO 7498-2 (1989): "Information processing systems - Open Systems
Interconnection - Basic Reference Model - Part 2: Security
Architecture".
ISO/IEC 13888-1 (2004): "IT security techniques - Non-repudiation -
Part 1: General".
ISO/IEC 9796-2 (2002): "Information technology - Security techniques
- Digital signature schemes giving message recovery - Part 2:
Integer factorization based mechanisms".
ISO/IEC 9796-4 (1998): "Digital signature schemes giving message
recovery - Part 4: Discrete logarithm based mechanisms".
ISO/IEC 10118-1 (2000): "Information technology - Security
techniques - Hash-functions - Part 1: General".
ISO/IEC 10118-2 (2000): "Information technology - Security
techniques - Hash-functions - Part 2: Hash-functions using an n-bit
block cipher algorithm".
ISO/IEC 10118-3 (2004): "Information technology - Security
techniques - Hash-functions - Part 3: Dedicated hash-functions".
ISO/IEC 10118-4 (1998): "Information technology - Security
techniques - Hash-functions - Part 4: Hash-functions using modular
arithmetic".
ISO/IEC 14888-1 (1998): "Information technology - Security
techniques - Digital signatures with appendix - Part 1: General".
Pinkas, Pope & Ross [Page 60]
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ISO/IEC 14888-2 (1999): "Information technology - Security
techniques - Digital signatures with appendix - Part 2: Identity-
based mechanisms".
ISO/IEC 14888-3 (1998): "Information technology - Security
techniques - Digital signatures with appendix - Part 3: Certificate-
based mechanisms".
ISO/IEC 15946-2 (2002): "Information technology - Security
techniques - Cryptographic techniques based on elliptic curves -
Part 2: Digital signatures".
ISO/IEC 15946-3 (2002): "Information technology - Security
techniques - Cryptographic techniques based on elliptic curves -
Part 3: Key establishment".
ISO/IEC 10181-5: Security Frameworks in Open Systems.
Non-Repudiation Framework. April 1997.
ITU-T Recommendation X.690 (2002): "Specification of basic encoding
rules for Abstract Syntax Notation One (ASN.1)".
CWA 14171 CEN Workshop Agreements: "General Guidelines for
Electronic Signature Verification".
XMLDSIG: W3C/IETF Recommendation (February 2002): "XML-Signature
Syntax and Processing".
ANSI X9.30-1 (1997): "Public Key Cryptography for the Financial
Services Industry - Part 1: The Digital Signature Algorithm (DSA)".
ANSI X9.30-2 (1997): "Public Key Cryptography for the Financial
Services Industry - Part 2: The Secure Hash Algorithm (SHA-1)".
ANSI X9.31-1 (1997): "Public Key Cryptography Using Reversible
Algorithms for the Financial Services Industry -
Part 1: The RSA Signature Algorithm".
ANSI X9.31-2 (1996): "Public Key Cryptography Using Reversible
Algorithms for the Financial Services Industry -
Part 2: Hash Algorithms".
ANSI X9.62 (1998): "Public Key Cryptography for the Financial
Services Industry - The Elliptic Curve Digital Signature Algorithm
(ECDSA)".
IEEE P1363 (2000): "Standard Specifications for Public-Key
Cryptography".
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12. Authors' addresses
Denis Pinkas
Bull S.A.
Rue Jean-Jaures
78340 Les Clayes sous Bois CEDEX
FRANCE
EMail: Denis.Pinkas@bull.net
Nick Pope
Security & Standards
192 Moulsham Street
Chelmsford, Essex
CM2 0LG
United Kingdom
EMail: pope@secstan.com
John Ross
Security & Standards
192 Moulsham Street
Chelmsford, Essex
CM2 0LG
United Kingdom
EMail: ross@secstan.com
This Informational RFC has been produced in ETSI TC-ESI.
ETSI
F-06921 Sophia Antipolis, Cedex - FRANCE
650 Route des Lucioles - Sophia Antipolis
Valbonne - France
Tel: +33 4 92 94 42 00 Fax: +33 4 93 65 47 16
secretariat@etsi.fr
http://www.etsi.org
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Annex A (normative): ASN.1 definitions
This annex provides a summary of all the ASN.1 syntax definitions for
new syntax defined in the present document.
A.1 Signature format definitions using X.208 ASN.1 syntax
NOTE: The ASN.1 module defined in clause A.1 using syntax defined in
ITU-T Recommendation X.208 [14] has precedence over that
defined in clause A.2 in the case of any conflict.
ETS-ElectronicSignatureFormats-ExplicitSyntax88 { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-mod(0)
eSignature-explicit88(28)}
DEFINITIONS EXPLICIT TAGS ::=
BEGIN
-- EXPORTS All
IMPORTS
-- Cryptographic Message Syntax (CMS): RFC 3852
ContentInfo, ContentType, id-data, id-signedData, SignedData,
EncapsulatedContentInfo, SignerInfo, id-contentType,
id-messageDigest, MessageDigest, id-signingTime, SigningTime,
id-countersignature, Countersignature
FROM CryptographicMessageSyntax2004
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) modules(0) cms-2004(24) }
-- ESS Defined attributes: RFC 2634 (Enhanced Security Services
-- for S/MIME)
id-aa-signingCertificate, SigningCertificate, IssuerSerial,
id-aa-contentReference, ContentReference, id-aa-contentIdentifier,
ContentIdentifier
FROM ExtendedSecurityServices
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0) ess(2) }
-- Internet X.509 Public Key Infrastructure - Certificate and CRL
-- Profile: RFC 3280
Certificate, AlgorithmIdentifier, CertificateList, Name,
DirectoryString, Attribute, BMPString, UTF8String
FROM PKIX1Explicit88
{iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-explicit(18)}
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GeneralNames, GeneralName, PolicyInformation
FROM PKIX1Implicit88
{iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) id-mod(0) id-pkix1-implicit (19)}
-- Internet Attribute Certificate Profile for Authorization - RFC 3281
AttributeCertificate
FROM PKIXAttributeCertificate {iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7)
id-mod(0) id-mod-attribute-cert(12)}
-- OCSP - RFC 2560
BasicOCSPResponse, ResponderID
FROM OCSP {iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-ocsp(14)}
-- Time Stamp Protocol RFC 3161
TimeStampToken
FROM PKIXTSP
{iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) id-mod(0) id-mod-tsp(13)};
-- S/MIME Object Identifier arcs used in the present document
-- ==========================================================
-- S/MIME OID arc used in the present document
-- id-smime OBJECT IDENTIFIER ::= { iso(1) member-body(2)
-- us(840) rsadsi(113549) pkcs(1) pkcs-9(9) 16 }
-- S/MIME Arcs
-- id-mod OBJECT IDENTIFIER ::= { id-smime 0 }
-- modules
-- id-ct OBJECT IDENTIFIER ::= { id-smime 1 }
-- content types
-- id-aa OBJECT IDENTIFIER ::= { id-smime 2 }
-- attributes
-- id-spq OBJECT IDENTIFIER ::= { id-smime 5 }
-- signature policy qualifier
-- id-cti OBJECT IDENTIFIER ::= { id-smime 6 }
-- commitment type identifier
-- Definitions of Object Identifier arcs used in the present document
-- ==================================================================
-- The allocation of OIDs to specific objects are given below with
-- the associated ASN.1 syntax definition
-- OID used referencing electronic signature mechanisms based on
-- the present document for use with the IDUP API (see annex D)
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id-etsi-es-IDUP-Mechanism-v1 OBJECT IDENTIFIER ::=
{ itu-t(0) identified-organization(4) etsi(0)
electronic-signature-standard (1733) part1 (1) idupMechanism (4)
etsiESv1(1) }
-- Basic ES CMS Attributes Defined in the present document
-- =======================================================
-- Mandatory RFC 3852 Electronic Signature Attributes
-- OtherSigningCertificate
id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 19 }
OtherSigningCertificate ::= SEQUENCE {
certs SEQUENCE OF OtherCertID,
policies SEQUENCE OF PolicyInformation OPTIONAL
-- NOT USED IN THE PRESENT DOCUMENT
}
OtherCertID ::= SEQUENCE {
otherCertHash OtherHash,
issuerSerial IssuerSerial OPTIONAL }
OtherHash ::= CHOICE {
sha1Hash OtherHashValue, -- This contains a SHA-1 hash
otherHash OtherHashAlgAndValue}
OtherHashValue ::= OCTET STRING
OtherHashAlgAndValue ::= SEQUENCE {
hashAlgorithm AlgorithmIdentifier,
hashValue OtherHashValue }
-- Policy ES Attributes Defined in the present document
-- ====================================================
-- Mandatory Basic Electronic Signature Attributes as above,
-- plus in addition.
-- Signature Policy Identifier
id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 15 }
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SignaturePolicy ::= CHOICE {
signaturePolicyId SignaturePolicyId,
signaturePolicyImplied SignaturePolicyImplied
-- not used in this version
}
SignaturePolicyId ::= SEQUENCE {
sigPolicyId SigPolicyId,
sigPolicyHash SigPolicyHash OPTIONAL,
sigPolicyQualifiers SEQUENCE SIZE (1..MAX) OF
SigPolicyQualifierInfo OPTIONAL
}
SignaturePolicyImplied ::= NULL
SigPolicyId ::= OBJECT IDENTIFIER
SigPolicyHash ::= OtherHashAlgAndValue
SigPolicyQualifierInfo ::= SEQUENCE {
sigPolicyQualifierId SigPolicyQualifierId,
sigQualifier ANY DEFINED BY sigPolicyQualifierId }
SigPolicyQualifierId ::= OBJECT IDENTIFIER
id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 1 }
SPuri ::= IA5String
id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 2 }
SPUserNotice ::= SEQUENCE {
noticeRef NoticeReference OPTIONAL,
explicitText DisplayText OPTIONAL}
NoticeReference ::= SEQUENCE {
organization DisplayText,
noticeNumbers SEQUENCE OF INTEGER }
DisplayText ::= CHOICE {
visibleString VisibleString (SIZE (1..200)),
bmpString BMPString (SIZE (1..200)),
utf8String UTF8String (SIZE (1..200)) }
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-- Optional Electronic Signature Attributes
-- Commitment Type
id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16}
CommitmentTypeIndication ::= SEQUENCE {
commitmentTypeId CommitmentTypeIdentifier,
commitmentTypeQualifier SEQUENCE SIZE (1..MAX) OF
CommitmentTypeQualifier OPTIONAL}
CommitmentTypeIdentifier ::= OBJECT IDENTIFIER
CommitmentTypeQualifier ::= SEQUENCE {
commitmentTypeIdentifier CommitmentTypeIdentifier,
qualifier ANY DEFINED BY commitmentTypeIdentifier }
id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 1}
id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 2}
id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 3}
id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 4}
id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 5}
id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 6}
-- Signer Location
id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 17}
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SignerLocation ::= SEQUENCE {
-- at least one of the following shall be present
countryName [0] DirectoryString OPTIONAL,
-- As used to name a Country in X.500
localityName [1] DirectoryString OPTIONAL,
-- As used to name a locality in X.500
postalAdddress [2] PostalAddress OPTIONAL }
PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString
-- Signer Attributes
id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18}
SignerAttribute ::= SEQUENCE OF CHOICE {
claimedAttributes [0] ClaimedAttributes,
certifiedAttributes [1] CertifiedAttributes }
ClaimedAttributes ::= SEQUENCE OF Attribute
CertifiedAttributes ::= AttributeCertificate
-- as defined in RFC 3281 : see clause 4.1
-- Content Timestamp
id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 20}
ContentTimestamp::= TimeStampToken
-- Signature Timestamp
id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 14}
SignatureTimeStampToken ::= TimeStampToken
-- Complete Certificate Refs.
id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21}
CompleteCertificateRefs ::= SEQUENCE OF OtherCertID
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-- Complete Revocation Refs
id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 22}
CompleteRevocationRefs ::= SEQUENCE OF CrlOcspRef
CrlOcspRef ::= SEQUENCE {
crlids [0] CRLListID OPTIONAL,
ocspids [1] OcspListID OPTIONAL,
otherRev [2] OtherRevRefs OPTIONAL
}
CRLListID ::= SEQUENCE {
crls SEQUENCE OF CrlValidatedID}
CrlValidatedID ::= SEQUENCE {
crlHash OtherHash,
crlIdentifier CrlIdentifier OPTIONAL}
CrlIdentifier ::= SEQUENCE {
crlissuer Name,
crlIssuedTime UTCTime,
crlNumber INTEGER OPTIONAL
}
OcspListID ::= SEQUENCE {
ocspResponses SEQUENCE OF OcspResponsesID}
OcspResponsesID ::= SEQUENCE {
ocspIdentifier OcspIdentifier,
ocspRepHash OtherHash OPTIONAL
}
OcspIdentifier ::= SEQUENCE {
ocspResponderID ResponderID, -- As in OCSP response data
producedAt GeneralizedTime -- As in OCSP response data
}
OtherRevRefs ::= SEQUENCE {
otherRevRefType OtherRevRefType,
otherRevRefs ANY DEFINED BY otherRevRefType
}
OtherRevRefType ::= OBJECT IDENTIFIER
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-- Certificate Values
id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23}
CertificateValues ::= SEQUENCE OF Certificate
-- Certificate Revocation Values
id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 24}
RevocationValues ::= SEQUENCE {
crlVals [0] SEQUENCE OF CertificateList OPTIONAL,
ocspVals [1] SEQUENCE OF BasicOCSPResponse OPTIONAL,
otherRevVals [2] OtherRevVals OPTIONAL}
OtherRevVals ::= SEQUENCE {
otherRevValType OtherRevValType,
otherRevVals ANY DEFINED BY otherRevValType
}
OtherRevValType ::= OBJECT IDENTIFIER
-- CAdES-C Timestamp
id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 25}
ESCTimeStampToken ::= TimeStampToken
-- Time-Stamped Certificates and CRLs
id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 26}
TimestampedCertsCRLs ::= TimeStampToken
-- Archive Timestamp
id-aa-ets-archiveTimestamp OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 27}
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ArchiveTimeStampToken ::= TimeStampToken
-- Attribute certificate references
id-aa-ets-attrCertificateRefs OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 44}
AttributeCertificateRefs ::= SEQUENCE OF OtherCertID
-- Attribute revocation references
id-aa-ets-attrRevocationRefs OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-aa(2) 45}
AttributeRevocationRefs ::= SEQUENCE OF CrlOcspRef
END
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A.2 Signature format definitions using X.680 ASN.1 syntax
NOTE: The ASN.1 module defined in clause A.2 has precedence over that
defined in clause A.2 using syntax defined in ITU-T
Recommendation X.680 (1997) [8] in the case of any conflict.
ETS-ElectronicSignatureFormats-ExplicitSyntax97 { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-mod(0)
eSignature-explicit97(29)}
DEFINITIONS EXPLICIT TAGS ::=
BEGIN
-- EXPORTS All -
IMPORTS
-- Cryptographic Message Syntax (CMS): RFC 3852
ContentInfo, ContentType, id-data, id-signedData, SignedData,
EncapsulatedContentInfo, SignerInfo,
id-contentType, id-messageDigest, MessageDigest, id-signingTime,
SigningTime, id-countersignature, Countersignature
FROM CryptographicMessageSyntax2004
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) modules(0) cms-2004(24) }
-- ESS Defined attributes: RFC 2634
-- (Enhanced Security Services for S/MIME)
id-aa-signingCertificate, SigningCertificate, IssuerSerial,
id-aa-contentReference, ContentReference, id-aa-contentIdentifier,
ContentIdentifier
FROM ExtendedSecurityServices
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0) ess(2) }
-- Internet X.509 Public Key Infrastructure
-- Certificate and CRL Profile: RFC 3280
Certificate, AlgorithmIdentifier, CertificateList, Name,
DirectoryString, Attribute,
FROM PKIX1Explicit88
{iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-pkix1-explicit(18)}
GeneralNames, GeneralName, PolicyInformation
FROM PKIX1Implicit88 {iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-pkix1-implicit(19)}
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-- Internet Attribute Certificate Profile for Authorization - RFC 3281
AttributeCertificate
FROM PKIXAttributeCertificate {iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-attribute-cert(12)}
-- OCSP RFC 2560
BasicOCSPResponse, ResponderID
FROM OCSP {iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-ocsp(14)}
-- RFC 3161 Internet X.509 Public Key Infrastructure
-- Time-Stamp Protocol (TSP)
TimeStampToken
FROM PKIXTSP {iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-tsp(13)}
maxSize
FROM ETS-ElectronicSignaturePolicies-97Syntax { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) id-mod(0) 8}
;
-- S/MIME Object Identifier arcs used in the present document
-- ==========================================================
-- S/MIME OID arc used in the present document
-- id-smime OBJECT IDENTIFIER ::= { iso(1) member-body(2)
-- us(840) rsadsi(113549) pkcs(1) pkcs-9(9) 16 }
-- S/MIME Arcs
-- id-mod OBJECT IDENTIFIER ::= { id-smime 0 }
-- modules
-- id-ct OBJECT IDENTIFIER ::= { id-smime 1 }
-- content types
-- id-aa OBJECT IDENTIFIER ::= { id-smime 2 }
-- attributes
-- id-spq OBJECT IDENTIFIER ::= { id-smime 5 }
-- signature policy qualifier
-- id-cti OBJECT IDENTIFIER ::= { id-smime 6 }
-- commitment type identifier
-- Definitions of Object Identifier arcs used in the present document
-- ==================================================================
-- The allocation of OIDs to specific objects are given below
-- with the associated ASN.1 syntax definition
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-- OID used referencing electronic signature mechanisms based
-- on the present document for use with the IDUP API (see annex D)
id-etsi-es-IDUP-Mechanism-v1 OBJECT IDENTIFIER ::=
{ itu-t(0) identified-organization(4) etsi(0)
electronic-signature-standard (1733) part1 (1) idupMechanism (4)
etsiESv1(1) }
-- Basic ES Attributes Defined in the present document
-- ===================================================
-- CMS Attributes Defined in the present document
-- Mandatory RFC 3852 Electronic Signature Attributes
-- OtherSigningCertificate
id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 19 }
OtherSigningCertificate ::= SEQUENCE {
certs SEQUENCE OF OtherCertID,
policies SEQUENCE OF PolicyInformation OPTIONAL
-- NOT USED IN THE PRESENT DOCUMENT
}
OtherCertID ::= SEQUENCE {
otherCertHash OtherHash,
issuerSerial IssuerSerial OPTIONAL }
OtherHash ::= CHOICE {
sha1Hash OtherHashValue, -- This contains a SHA-1 hash
otherHash OtherHashAlgAndValue}
OtherHashValue ::= OCTET STRING
OtherHashAlgAndValue ::= SEQUENCE {
hashAlgorithm AlgorithmIdentifier,
hashValue OtherHashValue }
-- Policy ES Attributes Defined in the present document
-- ====================================================
-- Mandatory Basic Electronic Signature Attributes, plus in addition.
-- Signature Policy Identifier
id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-aa(2) 15 }
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SignaturePolicy ::= CHOICE {
signaturePolicyId SignaturePolicyId,
signaturePolicyImplied SignaturePolicyImplied
-- not used in this version
}
SignaturePolicyId ::= SEQUENCE {
sigPolicyId SigPolicyId,
sigPolicyHash SigPolicyHash OPTIONAL,
sigPolicyQualifiers SEQUENCE SIZE (1..MAX) OF
SigPolicyQualifierInfo OPTIONAL
}
SignaturePolicyImplied ::= NULL
SigPolicyId ::= OBJECT IDENTIFIER
SigPolicyHash ::= OtherHashAlgAndValue
SigPolicyQualifierInfo ::= SEQUENCE {
sigPolicyQualifierId SIG-POLICY-QUALIFIER.&id
({SupportedSigPolicyQualifiers}),
qualifier SIG-POLICY-QUALIFIER.&Qualifier
({SupportedSigPolicyQualifiers}
{@sigPolicyQualifierId})OPTIONAL }
SupportedSigPolicyQualifiers SIG-POLICY-QUALIFIER ::=
{ noticeToUser | pointerToSigPolSpec }
SIG-POLICY-QUALIFIER ::= CLASS {
&id OBJECT IDENTIFIER UNIQUE,
&Qualifier OPTIONAL }
WITH SYNTAX {
SIG-POLICY-QUALIFIER-ID &id
[SIG-QUALIFIER-TYPE &Qualifier] }
noticeToUser SIG-POLICY-QUALIFIER ::= {
SIG-POLICY-QUALIFIER-ID id-spq-ets-unotice SIG-QUALIFIER-TYPE
SPUserNotice }
pointerToSigPolSpec SIG-POLICY-QUALIFIER ::= {
SIG-POLICY-QUALIFIER-ID id-spq-ets-uri SIG-QUALIFIER-TYPE SPuri }
id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 1 }
SPuri ::= IA5String
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id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) id-spq(5) 2 }
SPUserNotice ::= SEQUENCE {
noticeRef NoticeReference OPTIONAL,
explicitText DisplayText OPTIONAL}
NoticeReference ::= SEQUENCE {
organization DisplayText,
noticeNumbers SEQUENCE OF INTEGER }
DisplayText ::= CHOICE {
visibleString VisibleString (SIZE (1..200)),
bmpString BMPString (SIZE (1..200)),
utf8String UTF8String (SIZE (1..200)) }
-- Optional Electronic Signature Attributes
-- Commitment Type
id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16}
CommitmentTypeIndication ::= SEQUENCE {
commitmentTypeId CommitmentTypeIdentifier,
commitmentTypeQualifier SEQUENCE SIZE (1..MAX) OF
CommitmentTypeQualifier OPTIONAL}
CommitmentTypeIdentifier ::= OBJECT IDENTIFIER
CommitmentTypeQualifier ::= SEQUENCE {
commitmentQualifierId COMMITMENT-QUALIFIER.&id,
qualifier COMMITMENT-QUALIFIER.&Qualifier OPTIONAL }
COMMITMENT-QUALIFIER ::= CLASS {
&id OBJECT IDENTIFIER UNIQUE,
&Qualifier OPTIONAL }
WITH SYNTAX {
COMMITMENT-QUALIFIER-ID &id
[COMMITMENT-TYPE &Qualifier] }
id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 1}
id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 2}
id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 3}
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id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 4}
id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 5}
id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 6}
-- Signer Location
id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 17}
SignerLocation ::= SEQUENCE {
-- at least one of the following shall be present
countryName [0] DirectoryString{maxSize} OPTIONAL,
-- As used to name a Country in X.500
localityName [1] DirectoryString{maxSize} OPTIONAL,
-- As used to name a locality in X.500
postalAdddress [2] PostalAddress OPTIONAL }
PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString{maxSize}
-- Signer Attributes
id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18}
SignerAttribute ::= SEQUENCE OF CHOICE {
claimedAttributes [0] ClaimedAttributes,
certifiedAttributes [1] CertifiedAttributes }
ClaimedAttributes ::= SEQUENCE OF Attribute
CertifiedAttributes ::= AttributeCertificate
-- as defined in RFC 3281 : see clause 4.1
-- Content Timestamp
id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 20}
ContentTimestamp::= TimeStampToken
-- Signature Timestamp
id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 14}
SignatureTimeStampToken ::= TimeStampToken
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-- Complete Certificate Refs.
id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21}
CompleteCertificateRefs ::= SEQUENCE OF OtherCertID
-- Complete Revocation Refs
id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 22}
CompleteRevocationRefs ::= SEQUENCE OF CrlOcspRef
CrlOcspRef ::= SEQUENCE {
crlids [0] CRLListID OPTIONAL,
ocspids [1] OcspListID OPTIONAL,
otherRev [2] OtherRevRefs OPTIONAL
}
CRLListID ::= SEQUENCE {
crls SEQUENCE OF CrlValidatedID}
CrlValidatedID ::= SEQUENCE {
crlHash OtherHash,
crlIdentifier CrlIdentifier OPTIONAL}
CrlIdentifier ::= SEQUENCE {
crlissuer Name,
crlIssuedTime UTCTime,
crlNumber INTEGER OPTIONAL
}
OcspListID ::= SEQUENCE {
ocspResponses SEQUENCE OF OcspResponsesID}
OcspResponsesID ::= SEQUENCE {
ocspIdentifier OcspIdentifier,
ocspRepHash OtherHash OPTIONAL
}
OcspIdentifier ::= SEQUENCE {
ocspResponderID ResponderID, -- As in OCSP response data
producedAt GeneralizedTime -- As in OCSP response data
}
OtherRevRefs ::= SEQUENCE {
otherRevRefType OTHER-REVOCATION-REF.&id,
otherRevRefs SEQUENCE OF OTHER-REVOCATION-REF.&Type
}
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OTHER-REVOCATION-REF ::= CLASS {
&Type,
&id OBJECT IDENTIFIER UNIQUE }
WITH SYNTAX {
WITH SYNTAX &Type ID &id }
-- Certificate Values
id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23}
CertificateValues ::= SEQUENCE OF Certificate
-- Certificate Revocation Values
id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 24}
RevocationValues ::= SEQUENCE {
crlVals [0] SEQUENCE OF CertificateList OPTIONAL,
ocspVals [1] SEQUENCE OF BasicOCSPResponse OPTIONAL,
otherRevVals [2] OtherRevVals OPTIONAL}
OtherRevVals ::= SEQUENCE {
otherRevValType OTHER-REVOCATION-VAL.&id,
otherRevVals SEQUENCE OF OTHER-REVOCATION-REF.&Type
}
OTHER-REVOCATION-VAL ::= CLASS {
&Type,
&id OBJECT IDENTIFIER UNIQUE }
WITH SYNTAX {
WITH SYNTAX &Type ID &id }
-- CAdES-C Timestamp
id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 25}
ESCTimeStampToken ::= TimeStampToken
-- Time-Stamped Certificates and CRLs
id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 26}
TimestampedCertsCRLs ::= TimeStampToken
-- Archive Timestamp
id-aa-ets-archiveTimestamp OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 27}
ArchiveTimeStampToken ::= TimeStampToken
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-- Attribute certificate references
id-aa-ets-attrCertificateRefs OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 44}
AttributeCertificateRefs ::= SEQUENCE OF OtherCertID
-- Attribute revocation references
id-aa-ets-attrRevocationRefs OBJECT IDENTIFIER ::= { iso(1) member-
body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 45}
AttributeRevocationRefs ::= SEQUENCE OF CrlOcspRef
END
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Annex B (informative): Extended forms of Electronic Signatures
Clause 4 provides on overview of the various formats of electronic
signatures included in the present document. This annex lists the
attributes that need to be present in the various extended electronic
signature formats and provide example validation sequences using the
extended formats.
B.1 Extended forms of validation data
The complete validation data (CAdES-C) described in clause 4.3 and
illustrated in figure 3 may be extended to create Electronic Signatures
with extended validation data. Some Electronic Signatures forms that
include extended validation are explained below.
An X-Long electronic signature (CAdES-X Long) is when the values of the
certificates and revocation information are added to the CAdES-C.
This form of Electronic Signature can be useful when the verifier does
not have direct access to the following information:
- the signer's certificate;
- all the CA certificates that make up the full certification path;
- all the associated revocation status information, as referenced
in the CAdES-C.
In some situations additional time-stamps may be created and added to
the Electronic Signatures as additional attributes. For example:
- time-stamping all the validation data as held with the ES (CAdES-
C), this eXtended validation data is called a CAdES-X Type 1; or
- time-stamping individual reference data as used for complete
validation. This form of eXtended validation data is called an
CAdES-X Type 2.
NOTE 1: The advantages/drawbacks for CAdES-X Type 1 and CAdES-X Type 2
are discussed in clause C.4.4.
The above time-stamp forms can be useful when it is required to counter
the risk that any CA keys used in the certificate chain may be
compromised.
A combination of the two formats above may be used. This form of
eXtended validation data is called an ES X-Long Type 1 or CAdES-X Long
Type 2. This form of Electronic Signature can be useful when the
verifier needs both the values and proof of when the validation data
existed.
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NOTE 2: The advantages/drawbacks for CAdES-X long Type 1 and CAdES-X
long Type 2 are discussed in clause C.4.6.
B.1.1 CAdES-X Long
An Electronic Signature with the additional validation data forming the
CAdES-X Long form (CAdES-X-Long)) is illustrated in figure B.1 and
comprises the following:
- CAdES-BES or CAdES-EPES as defined in clauses 4.3 , 5.7 or 5.8;
- complete-certificate-references attribute as defined in clause
6.2.1;
- complete-revocation-references attribute as defined in clause
6.2.2.
The following attributes are required if a TSP is not providing a time-
mark of the ES:
- signature-time-stamp attribute as defined in clause 6.1.1.
The following attributes are required if the full certificate values
and revocation values are not already included in the CAdES-BES or
CAdES-EPES:
- certificate-values attribute as defined in clause 6.3.3;
- revocation-values attribute, as defined in clause 6.3.4.
If attributes certificates are used then the following attributes may
be present:
- attribute-certificate-references attribute defined in clause
6.2.3;
- attribute-revocation-references attribute as defined in clause
6.2.4.
Other unsigned attributes may be present, but are not required.
NOTE: Attribute certificate and revocation references are only
present if a user attribute certificate is present in the
electronic signature, see clauses 6.2.2 and 6.2.3.
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+---------------------- CAdES-X-Long --------------------------------+
|+-------------------------------------- CAdES-C ---+ |
|| +----------+ | +-------------+|
||+----- CAdES-BES or CAdES-EPES ----+ |Timestamp | | | ||
||| | |over | | | Complete ||
|||+---------++----------++---------+| |digital | | | certificate ||
|||| || || || |signature | | | and ||
||||Signer's || Signed ||Digital || | | | | revocation ||
||||Document ||Attributes||signature|| |Optional | | | data ||
|||| || || || |when | | | ||
|||+---------++----------++---------+| |timemarked| | | ||
||+----------------------------------+ +----------+ | | ||
|| +-----------+| +-------------+|
|| |Complete || |
|| |certificate|| |
|| |and || |
|| |revocation || |
|| |references || |
|| +-----------+| |
|+--------------------------------------------------+ |
| |
+--------------------------------------------------------------------+
Figure B.1 : Illustration of CAdES-X-Long
B.1.2 CAdES-X Type 1
An Electronic Signature with the additional validation data forming the
eXtended Validation Data - Type 1 X is illustrated in figure B.2 and
comprises the following:
- the CAdES-BES or CAdES-EPES as defined in clauses 4.2, 5.7 or
5.8;
- complete-certificate-references attribute as defined in clause
6.2.1;
- complete-revocation-references attribute as defined in clause
6.2.2;
- CAdES-C-Timestamp attribute, as defined in clause 6.3.5.
The following attributes are required if a TSP is not providing a time-
mark of the ES:
- signature-time-stamp attribute as defined in clause 6.1.1.
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If attributes certificates are used then the following attributes may
be present:
- attribute-certificate-references attribute defined in clause
6.2.3;
- attribute-revocation-references attribute as defined in clause
6.2.4.
Other unsigned attributes may be present, but are not required.
+------------------------ CAdES-X-Type 1 ----------------------------+
|+---------------------------------- CAdES-C ------+ |
|| +----------+ | +-------------+ |
||+--- CAdES-BES or CAdES-EPES ------+|Timestamp | | | | |
||| ||over | | | | |
|||+---------++----------++---------+||digital | | | | |
||||Signer's || Signed || Digital |||signature | | | Timestamp | |
||||Document ||Attributes||signature||| | | | over | |
|||| || || |||Optional | | | CAdES-C | |
|||+---------++----------++---------+||when | | | | |
||+----------------------------------+|timemarked| | | | |
|| +----------+ | | | |
|| +-----------+| +-------------+ |
|| |Complete || |
|| |certificate|| |
|| | and || |
|| |revocation || |
|| |references || |
|| +-----------+| |
|+-------------------------------------------------+ |
| |
+--------------------------------------------------------------------+
Figure B.2 : Illustration of CAdES-X Type 1
B.1.3 CAdES-X Type 2
An Electronic Signature with the additional validation data forming the
eXtended Validation Data - Type 2 X is illustrated in figure B.3. and
comprises the following:
- CAdES-BES or CAdES-EPES as defined in clauses 4.2, 5.7 or 5.8;
- complete-certificate-references attribute as defined in clause
6.2.1;
- complete-revocation-references attribute as defined in clause
6.2.2;
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- time-stamped-certs-crls-references attribute as defined in clause
6.3.6.
The following attributes are required if a TSP is not providing a time-
mark of the ES:
- signature-time-stamp attribute as defined in clause 6.1.1.
If attributes certificates are used then the following attributes may
be present:
- attribute-certificate-references attribute defined in clause
6.2.3;
- attribute-revocation-references attribute as defined in clause
6.2.4.
Other unsigned attributes may be present, but are not required.
+----------------------- CAdES-X-Type 2 -----------------------------+
|+-------------------------------------- CAdES-C --+ |
|| +----------+ | |
||+-- CAdES-BES or CAdES-EPES -------+|Timestamp | | |
||| ||over | | |
|||+---------++----------++---------+||digital | | +-------------+ |
|||| || || |||Signature | | | Timestamp | |
||||Signer's || Signed || Digital ||| | | | only over | |
||||Document ||Attributes||signature|||Optional | | | Complete | |
|||| || || |||when | | | certificate | |
|||+---------++----------++---------+||Timemarked| | | and | |
||+----------------------------------++----------+ | | revocation | |
|| +-----------+| | references | |
|| |Complete || +-------------+ |
|| |certificate|| |
|| |and || |
|| |revocation || |
|| |references || |
|| +-----------+| |
|+-------------------------------------------------+ |
| |
+--------------------------------------------------------------------+
Figure B.3 : Illustration of CAdES-X Type 2
B.1.4 CAdES-X Long Type 1 and CAdES-X Long Type 2
An Electronic Signature with the additional validation data forming the
CAdES-X Long Type 1 and CAdES-X Long Type 2 is illustrated in
figure B.4 and comprises the following:
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- CAdES-BES or CAdES-EPES as defined in clauses 4.3, 5.7 or 5.8;
- complete-certificate-references attribute as defined in clause
6.2.1;
- complete-revocation-references attribute as defined in clause
6.2.2;
The following attributes are required if a TSP is not providing a time-
mark of the ES:
- signature-time-stamp attribute as defined in clause 6.1.1.
The following attributes are required if the full certificate values
and revocation values are not already included in the CAdES-BES or
CAdES-EPES:
- certificate-values attribute as defined in clause 6.3.3;
- revocation-values attribute, as defined in clause 6.3.4.
If attributes certificates are used then the following attributes may
be present:
- attribute-certificate-references attribute defined in clause
6.2.3;
- attribute-revocation-references attribute as defined in clause
6.2.4.
Plus one of the following attributes is required:
- CAdES-C-Timestamp attribute, as defined in clause 6.3.5;
- time-stamped-certs-crls-references attribute as defined in clause
6.3.6.
Other unsigned attributes may be present, but are not required.
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+---------------------- CAdES-X-Type 1 or 2 ------------------------+
| +--------------+|
|+-------------------------------------- CAdES-C --+|+------------+||
|| +----------+ ||| Timestamp |||
||+-- CAdES-BES or CAdES-EPES -------+|Timestamp | ||| over |||
||| ||over | ||| CAdES-C |||
|||+---------++----------++---------+||digital | | +------------+ |
|||| || || |||signature | || or ||
||||Signer's || Signed || Digital ||| | ||+------------+||
||||Document ||Attributes||Signature|||Optional | ||| Timestamp |||
|||| || || |||when | ||| only over |||
|||+---------++----------++---------+||timemarked| ||| complete |||
||+----------------------------------++----------+ ||| certificate|||
|| ||| and |||
|| +-----------+||| revocation |||
|| |Complete |||| references |||
|| |certificate|||+------------+||
|| |and ||+--------------+|
|| |revocation || +------------+ |
|| |references || |Complete | |
|| +-----------+| |certificate | |
|+-------------------------------------------------+ | and | |
| |revocation | |
| | values | |
| +------------+ |
+-------------------------------------------------------------------+
Figure B.4 : Illustration of CAdES-X Long Type 1
and CAdES-X Long Type 2
B.2 Timestamp extensions
Each instance of time-stamp attribute may include as unsigned
attributes in the signedData of the timestamp the following attribute
related to the TSU:
- complete-certificate-references attribute of the TSU as defined
in clause 6.2.1;
- complete-revocation-references attribute of the TSU as defined in
clause 6.2.2;
- certificate-values attribute; of the TSU as defined in clause
6.3.3;
- revocation-values attribute, of the TSU as defined in clause
6.3.4.
Other unsigned attributes may be present, but are not required.
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B.3 Archive validation data (CAdES-A)
Before the algorithms, keys and other cryptographic data used at the
time the CAdES-C was built become weak and the cryptographic functions
become vulnerable, or the certificates supporting previous time-stamps
expires, the signed data, the CAdES-C and any additional information
(i.e. any CAdES-X) should be time-stamped. If possible this should use
stronger algorithms (or longer key lengths) than in the original time-
stamp. This additional data and time-stamp is called Archive
Validation Data required for the ES Archive format (CAdES-A). The
Time-stamping process may be repeated every time the protection used to
time-stamp a previous CAdES-A becomes weak. An CAdES-A may thus bear
multiple embedded time stamps.
An example of an Electronic Signature (ES), with the additional
validation data for the CAdES-C and CAdES-X forming the CAdES-A is
illustrated in figure B.5.
+--------------------------- CAdES-A---------------------------------+
|+----------------------------------------------------+ |
|| +--------------+| +----------+ |
||+--------------------- CAdES-C ----+|+------------+|| | | |
||| +----------+ ||| Timestamp ||| | | |
|||+-- CAdES-BES ------+|Timestamp | ||| over ||| | | |
|||| or CAdES-EPES ||over | ||| CAdES-C ||| | Archive | |
|||| ||digital | ||+------------+|| | | |
|||| ||signature | || or || |Timestamp | |
|||| || | ||+------------+|| | | |
|||| ||optional | ||| Timestamp ||| | | |
|||| ||when | ||| only over ||| | | |
|||| ||timemarked| ||| complete ||| | | |
|||+-------------------++----------+ ||| certificate||| +----------+ |
||| ||| and ||| |
||| +-------------+||| revocation ||| |
||| | Complete |||| references ||| |
||| | certificate |||+------------+|| |
||| | and ||+--------------+| |
||| | revocation || +------------+ | |
||| | references || |Complete | | |
||| +-------------+| |certificate | | |
||+----------------------------------+ | and | | |
|| |revocation | | |
|| | values | | |
|| +------------+ | |
|+----------------------------------------------------+ |
+--------------------------------------------------------------------+
Figure B.5 : Illustration of CAdES-A
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The CAdES-A comprises the following elements:
- the CAdES-BES or CAdES-EPES including their signed and unsigned
attributes;
- complete-certificate-references attribute as defined in clause
6.2.1;
- complete-revocation-references attribute as defined in clause
6.2.2.
The following attributes are required if a TSP is not providing a time-
mark of the ES:
- signature-time-stamp attribute as defined in clause 6.1.1.
If attributes certificates are used then the following attributes may
be present:
- attribute-certificate-references attribute defined in clause
6.2.3;
- attribute-revocation-references attribute as defined in clause
6.2.4.
The following attributes are required if the full certificate values
and revocation values are not already included in the CAdES-BES or
CAdES-EPES:
- certificate-values attribute as defined in clause 6.3.3;
- revocation-values attribute as defined in clause 6.3.4.
At least one of the following two attributes is required:
- CAdES-C-Timestamp attribute as defined in clause 6.3.5;
- time-stamped-certs-crls-references attribute as defined in clause
6.3.6.
The following attribute is required:
- archive-time-stamp attributes defined in clause 6.4.1.
Several instances of archive-time-stamp attribute may occur with an
electronic signature both over time and from different TSUs. The time-
stamp should be created using stronger algorithms (or longer key
lengths) than in the original electronic signatures or time-stamps.
Other unsigned attributes of the ES may be present, but are not
required.
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The archive timestamp will itself contain the certificate and
revocation information required to validate the archive timestamp, this
may include the following unsigned attributes:
- complete-certificate-references attribute of the TSU as defined
in clause 6.2.1;
- complete-revocation-references attribute of the TSU as defined in
clause 6.2.2;
- certificate-values attribute of the TSU as defined in clause
6.3.3;
- revocation-values attribute of the TSU as defined in clause
6.3.4.
Other unsigned attributes may be present, but are not required.
B.4 Example validation sequence
As described earlier the signer or initial verifier may collect all the
additional data that forms the electronic signature. Figure B.6, and
subsequent description, describes how the validation process may build
up a complete electronic signature over time.
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+------------------------------------------ CAdES-C -------------+
|+------------------------------- CAdES-T ------+ |
||+-------------- CAdES ------------+ | |
|||+--------------------++---------+|+---------+| +-----------+ |
|||| ________ || |||Timestamp|| |Complete | |
|||||Sign.Pol| ||Digital |||over || |certificate| |
||||| Id. | Signed ||signature|||digital || | and | |
||||| option.|attributes|| |||signature|| |revocation | |
|||||________| |+---------+|+---------+| |references | |
|||+--------------------+ | ^ | +-----------+ |
||+---------------------------------+ | | ^ |
|| 1 | / | | |
|+---------------------- | ------------/--------+ | |
+----------------------- | ---------- / --------------- / -------+
| /2 ----3--------
+----------+ | / /
| | v / |
| Signer's | +---------------------+ +-------------+
| document |----->| Validation Process |---->|- Valid |
| | +---------------------+ 4 |- Invalid |
+----------+ | ^ | ^ |- Validation |
v | v | | Incomplete |
+---------+ +--------+ +-------------+
|Signature| |Trusted |
| Policy | |Service |
| Issuer | |Provider|
+---------+ +--------+
Figure B.6 : Illustration of a CAdES validation sequence
Soon after receiving the Electronic Signature (CAdES) from the signer
(1), the digital signature value may be checked; the validation process
shall at least add a time-stamp (2), unless the signer has provided one
which is trusted by the verifier. The validation process may also
validate the electronic signature, using additional data (e.g.
certificates, CRL, etc.) provided by trusted service providers. When
applicable, the validation process will also need to conform to the
requirements specified in a signature policy. If the validation
process is validation incomplete, then the output from this stage is
the CAdES-T.
To ascertain the validity status as Valid or Invalid and communicate
that to the user (4) all the additional data required to validate the
CAdES-C, must be available (e.g. the complete certificate and
revocation information).
Once the data needed to complete validation data references (CAdES-C)
is available then the validation process should:
- obtain all the necessary additional certificate and revocation
status information;
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- complete all the validation checks on the ES, using the complete
certificate and revocation information (if a time-stamp is not
already present, this may be added at the same stage combining
CAdES-T and CAdES-C process);
- record the complete certificate and revocation references (3);
- indicate the validity status to the user (4).
At the same time as the validation process creates the CAdES-C, the
validation process may provide and/or record the values of certificates
and revocation status information used in CAdES-C, called the CAdES-X
Long (5).
This is illustrated in figure B.7.
+----------------------------------------------------- CAdES-X Long -+
|+------------------------------- CAdES-C -------------+ |
||+-------------- CAdES ------------+ | |
|||+--------------------++---------+|+---------+ |+-----------+|
|||| ________ || |||Timestamp| ||Complete ||
|||||Sign.Pol| ||Digital |||over | ||certificate||
||||| Id. | Signed ||signature|||digital | || and ||
||||| option.|attributes|| |||signature| ||revocation ||
|||||________| || ||+---------+ || values ||
|||+--------------------++---------+| ^ +-----------+|+-----------+|
||+---------------------------------+ | |Complete || ^ |
|| | | |certificate|| | |
|| | 2 | | and || | |
|| | | |revocation || | |
|| | | |references || | |
|| 1 | / +-----------+| | |
|+------------------------ | ------- / --------- ^-----+ / |
+------------------------- | ------ / ---------- |--------- / -------+
| / ----- / ------- /
+----------+ | / / 3 / 5
| | v | | |
| Signer's | +--------------------+ +-----------+
| document |----->| Validation Process |----->| - Valid |
| | +--------------------+ 4 | - Invalid |
+----------+ | ^ | ^ +-----------+
v | v |
+---------+ +--------+
|Signature| |Trusted |
| Policy | |Service |
| Issuer | |Provider|
+---------+ +--------+
Figure B.7 : Illustration of a CAdES validation sequence
with CAdES-X Long
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When the validation process creates the CAdES-C it may also create
extended forms of validation data.
A first alternative is to time-stamp all data forming the CAdES-X Type
1 (6).
This is illustrated in figure B.8.
+------------------------------------------------ CAdES-X Type 1 -----+
|+------------------------------- CAdES-C ------------------+ |
||+-------------- CAdES ------------+ | |
|||+--------------------++---------+|+---------++----------+|+-------+|
|||| ________ || |||Timestamp|| Complete ||| ||
|||||Sign.Pol| ||Digital |||over || cert. |||Time- ||
||||| Id. | Signed ||signature|||digital || and |||stamp ||
||||| option.|attributes|| |||signature|| revoc. ||| over ||
|||||________| |+---------+|+---------+|references|||CAdES-C||
|||+--------------------+ | ^ | ||| ||
||+---------------------------------+ | +----------+|+-------+|
|| | | ^ | ^ |
|| 1 | / | | | |
|+------------------------ | --------- / ----------- / -----+ | |
+------------------------- | -------- / ----------- / --------- / ----+
| 2 / ---3---- /
+----------+ | / / -----------5------
| | v | | /
| Signer's | +--------------------+ +-----------+
| document |----->| Validation Process |-----> | - Valid |
| | +--------------------+ 4 | - Invalid |
+----------+ | ^ | ^ +-----------+
v | v |
+---------+ +--------+
|Signature| |Trusted |
| Policy | |Service |
| Issuer | |Provider|
+---------+ +--------+
Figure B.8 : Illustration of CAdES with eXtended Validation Data
CAdES-X Type 1
Another alternative is to time-stamp the certificate and revocation
information references used to validate the electronic signature (but
not the signature) (6'); this is called CAdES-X Type 2.
This is illustrated in figure B.9.
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+-------------------------------------------- CAdES-X Type 2 --------+
|+------------------------------- CAdES-C -------------+ |
||+-------------- CAdES ------------+ | |
|||+--------------------++---------+|+---------+ |+-----------+|
|||| ________ || |||Timestamp| ||Timestamp ||
|||||Sign.Pol| || |||over | || over ||
||||| Id. | Signed ||Digital |||digital | ||complete ||
||||| option.|attributes||signature|||signature| ||certificate||
|||||________| || ||| | || ||
|||+--------------------++---------+|+---------+ || and ||
||+---------------------------------+ ^ +-----------+||revocation ||
|| | | |Complete |||references ||
|| | | |certificate||+-----------+|
|| | | | and || ^ |
|| 1 | 2 | |revocation || | |
|| | | |references || | |
|| | | +-----------+| | |
|+------------------------ | --------- | --- ^ --------+ | |
| | | 3 | / |
| | | / ---------- |
| | / / / 5 |
| | / / / |
| | / / / |
+------------------------- | ----- | -- | -- / ----------------------+
| | | |
v | | |
+--------------------+ +-----------+
| Validation Process |----->| - Valid |
+--------------------+ 4 | - Invalid |
| ^ | ^ +-----------+
v | v |
+---------+ +--------+
|Signature| |Trusted |
| Policy | |Service |
| Issuer | |Provider|
+---------+ +--------+
Figure B.9: Illustration of CAdES with eXtended Validation Data
CAdES-X Type 2
Before the algorithms used in any of electronic signatures become or
are likely, to be compromised or rendered vulnerable in the future, it
may be necessary to time-stamp the entire electronic signature,
including all the values of the validation and user data as an ES with
Archive Validation Data (CAdES-A) (7).
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An CAdES-A is illustrated in figure B.10.
+----------------------------- CAdES-A ---------------------------+
| |
| +-- CAdES-X Long Type 1 or 2 ----------+ |
| | | +------------+ |
| | | | | |
| | | | Archive | |
| | | | Time-stamp | |
| | | | | |
| | | +------------+ |
| +---------------------------------------+ ^ |
| +----------+ ^ ^ ^ ^ | |
| | | | | | | / |
| | Signers' | | | | | / |
| | Document |\ | | | | / |
| | | \ 1 2 | 3 | 5 | 6 | 7 / |
| +----------+ \ | | | | / |
| \ | | | | / |
+----------------- \ --- | - | - | - | ------ / ------------------+
\ | | | | |
| | | | | |
| | | | | |
v v | | | |
+-----------------------------+ +-----------+
| Validation Process |----->| - Valid |
+-----------------------------+ 4 | - Invalid |
| ^ | ^ +-----------+
v | v |
+---------+ +--------+
|Signature| |Trusted |
| Policy | |Service |
| Issuer | |Provider|
+---------+ +--------+
Figure B.10: Illustration of CAdES-A
B.5 Additional optional features
The present document also defines additional optional features to:
- indicate a commitment type being made by the signer;
- indicate the claimed time when the signature was done;
- indicate the claimed location of the signer;
- indicate the claimed or certified role under which a signature
was created;
- support counter signatures;
- support multiple signatures.
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Annex C (informative):General description
This annex explains some of the concepts and provides the rational for
normative parts of the present document.
The specification below includes a description why and when the each
component of an electronic signature is useful, with a brief
description of the vulnerabilities and threats and the manner by which
they are countered.
C.1 The signature policy
The signature policy is a set of rules for the creation and validation
of an electronic signature, under which the signature can be determined
to be valid. A given legal/contractual context may recognize a
particular signature policy as meeting its requirements. A signature
policy may be issued, for example, by a party relying on the electronic
signatures and selected by the signer for use with that relying party.
Alternatively, a signature policy may be established through an
electronic trading association for use amongst its members. Both the
signer and verifier use the same signature policy.
The signature policy may be explicitly identified or may be implied by
the semantics of the data being signed and other external data like a
contract being referenced which itself refers to a signature policy.
An explicit signature policy has a globally unique reference, which is
bound to an electronic signature by the signer as part of the signature
calculation.
The signature policy needs to be available in human readable form so
that it can be assessed to meet the requirements of the legal and
contractual context in which it is being applied. To facilitate the
automatic processing of an electronic signature the parts of the
signature policy which specifies the electronic rules for the creation
and validation of the electronic signature also needs to be
comprehensively defined and in a computer processable form.
The signature policy thus includes the following:
- rules, which apply to technical validation of a particular
signature;
- rules which may be implied through adoption of Certificate
Policies that apply to the electronic signature (e.g. rules for
ensuring the secrecy of the private signing key);
- rules, which relate to the environment used by the signer, e.g.
the use of an agreed CAD (Card Accepting Device) used in
conjunction with a smart card.
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For example, the major rules required for technical validation can
include: recognized root keys or "top-level certification authorities",
acceptable certificate policies (if any), necessary certificate
extensions and values (if any), the need for the revocation status for
each component of the certification tree, acceptable TSAs (if time-
stamp tokens are being used), acceptable organizations for keeping the
audit trails with time-marks (if time-marking is being used),
acceptable AAs (if any are being used).as well as rules defining the
components of the electronic signature that shall be provided by the
signer with data required by the verifier when required to provide long
term proof.
C.2 Signed information
The information being signed may be defined as a MIME-encapsulated
message which can be used to signal the format of the content in order
to select the right display or application. It can be composed of
formatted data, free text or fields from an electronic form (e-form).
For example, the Adobe(tm) format "pdf" may be used or the eXtensible Mark
up Language (XML). Annex D defines how the content may be structured
to indicate the type of signed data using MIME.
C.3 Components of an electronic signature
C.3.1 Reference to the signature policy
When two independent parties want to evaluate an electronic signature,
it is fundamental that they get the same result. This requirement can
be met using comprehensive signature policies that ensure consistency
of signature validation. Signature policies can be identified
implicitly by the data being signed or they can be explicitly
identified using the CAdES-EPES form of electronic signature, the
CAdES-EPES mandates a consistent signature policy must be used by both
the signer and verifier.
By signing over the signature policy identifier in the CAdES-EPES the
signer explicitly indicates that he or she has applied the signature
policy in creating the signature.
In order to unambiguously identify the details of an explicit signature
policy that is to be used to verify a CAdES-EPES the signature an
identifier and hash of the "Signature policy" shall be part of the
signed data. Additional information about the explicit policy (e.g.
web reference to the document) may be carried as "qualifiers" to the
signature policy identifier.
In order to unambiguously identify the authority responsible for
defining an explicit signature policy the "Signature policy" can be
signed.
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C.3.2 Commitment type indication
The commitment type can be indicated in the electronic signature
either:
- explicitly using a "commitment type indication" in the electronic
signature;
- implicitly or explicitly from the semantics of the signed data.
If the indicated commitment type is explicit using a "commitment type
indication" in the electronic signature, acceptance of a verified
signature implies acceptance of the semantics of that commitment type.
The semantics of explicit commitment types indications may be subject
to signer and verifier agreement, specified as part of the signature
policy or registered for generic use across multiple policies.
If a CAdES-EPES electronic signature format is used and the electronic
signature includes a commitment type indication other than one of those
recognized under the signature policy the signature shall be treated as
invalid.
How commitment is indicated using the semantics of the data being
signed is outside the scope of the present document.
NOTE: Examples of commitment indicated through the semantics of the
data being signed, are:
- an explicit commitment made by the signer indicated by the type
of data being signed over. Thus, the data structure being signed
can have an explicit commitment within the context of the
application (e.g. EDIFACT purchase order);
- an implicit commitment which is a commitment made by the signer
because the data being signed over has specific semantics
(meaning) which is only interpretable by humans, (i.e. free
text).
C.3.3 Certificate identifier from the signer
In many real life environments users will be able to get from different
CAs or even from the same CA, different certificates containing the
same public key for different names. The prime advantage is that a
user can use the same private key for different purposes. Multiple use
of the private key is an advantage when a smart card is used to protect
the private key, since the storage of a smart card is always limited.
When several CAs are involved, each different certificate may contain a
different identity, e.g. as a national or as an employee from a
company. Thus when a private key is used for various purposes, the
certificate is needed to clarify the context in which the private key
was used when generating the signature. Where there is the possibility
of multiple use of private keys it is necessary for the signer to
indicate to the verifier the precise certificate to be used.
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Many current schemes simply add the certificate after the signed data
and thus are vulnerable to substitution attacks. If the certificate
from the signer was simply appended to the signature and thus not
protected by the signature, any one could substitute one certificate by
another and the message would appear to be signed by some one else. In
order to counter this kind of attack, the identifier of the signer has
to be protected by the digital signature from the signer.
In order to identify unambiguously the certificate to be used for the
verification of the signature an identifier of the certificate from the
signer shall be part of the signed data.
C.3.4 Role attributes
While the name of the signer is important, the position of the signer
within a company or an organization of paramount importance as well.
Some information (i.e. a contract) may only be valid if signed by a
user in a particular role, e.g. a Sales Director. In many cases who
the sales Director really is, is not that important but being sure that
the signer is empowered by his company to be the Sales Director is
fundamental.
The present document defines two different ways for providing this
feature:
- by placing a claimed role name in the CMS signed attributes
field;
- by placing an attribute certificate containing a certified role
name in the CMS signed attributes field.
NOTE: Another possible approach would have been to use additional
attributes containing the roles name(s) in the signer's
identity certificate However, it was decided not to follow
this approach as it significantly complicates the management
of certificates. For example by using separate certificates
for signer's identity and roles means new identity keys need
not be issued if a user's role changes.
C.3.4.1 Claimed role
The signer may be trusted to state his own role without any certificate
to corroborate this claim. In which case the claimed role can be added
to the signature as a signed attribute.
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C.3.4.2 Certified role
Unlike public key certificates that bind an identifier to a public key,
Attribute Certificates bind the identifier of a certificate to some
attributes, like a role. An Attribute Certificate is NOT issued by a
CA but by an Attribute Authority (AA). The Attribute Authority in most
cases might be under the control of an organization or a company that
is best placed to know which attributes are relevant for which
individual. The Attribute Authority may use or point to public key
certificates issued by any CA, provided that the appropriate trust may
be placed in that CA. Attribute Certificates may have various periods
of validity. That period may be quite short, e.g. one day. While this
requires that a new Attribute Certificate be obtained every day, valid
for that day, this can be advantageous since revocation of such
certificates may not be needed. When signing, the signer will have to
specify which Attribute Certificate it selects. In order to do so, the
Attribute Certificate will have to be included in the signed data in
order to be protected by the digital signature from the signer.
In order to identify unambiguously the attribute certificate(s) to be
used for the verification of the signature an identifier of the
attribute certificate(s) from the signer shall be part of the signed
data.
C.3.5 Signer location
In some transactions the purported location of the signer at the time
he or she applies his signature may need to be indicated. For this
reason an optional location indicator shall be able to be included.
In order to provide indication of the location of the signer at the
time he or she applied his signature a location attribute may be
included in the signature.
C.3.6 Signing time
The present document provides the capability to include a claimed
signing time as an attribute of an electronic signature.
Using this attribute a signer may sign over a time which is the claimed
signing time. When an ES with Time-stamp is created (CAdES-T) then
either a trusted time stamp is obtained and added to the ES or a
trusted time mark exists in an audit trail. When a verifier accepts a
signature, the two times shall be within acceptable limits. In all
cases, the claimed signing time cannot be after the time identified by
the time-stamp or time-mark.
A further optional attribute is defined in the present document to
timestamp the content, to provide proof of the existence of the
content, at the time indicated by the time-stamp token.
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Using this optional attribute a trusted secure time may be obtained
before the document is signed and included under the digital signature.
This solution requires an on-line connection to a trusted time-stamping
service before generating the signature and may not represent the
precise signing time, since it can be obtained in advance. However,
this optional attribute may be used by the signer to prove that the
signed object existed before the date included in the time-stamp (see
clause 5.11.4).
Also, the signing time, if present should be between the time indicated
by this time-stamp and time indicated by the CAdES-T time-stamp.
C.3.7 Content format
When presenting signed data to a human user it may be important that
there is no ambiguity as to the presentation of the signed information
to the relying party. In order for the appropriate representation
(text, sound or video) to be selected by the relying party a content
hint may be indicated by the signer. If a relying party system does
not use the format specified in the content hints attribute to present
the data to the relying party, then a human relying party may
misinterpret data with valid signatures.
C.3.8 Content cross referencing
When presenting a signed data is in related to another signed data, it
may be important to identify the signed data to which it relates to.
The Content-reference and Content-identifier attributes as defined in
ESS (RFC 2634 [5]) provide the ability to link a request and reply
messages in an exchange between two parties.
C.4 Components of validation data
C.4.1 Revocation status information
A verifier will have to ascertain that the certificate of the signer
was valid at the time of the signature. This can be done by either:
- using Certificate Revocation Lists (CRLs);
- using responses from an on-line certificate status server (for
example; obtained through the OCSP protocol).
NOTE 1: The time of the signature may not be know, so time-stamping
or time-marking may be used to provide the time indication of
when it was known the signature existed.
NOTE 2: When validating an electronic signature and checking
revocation status information a "grace period" is required
which needs to be suitably long enough to allow the involved
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authority to process a "last minute" revocation request and
for the request to propagate through the revocation system.
This grace period is to be added to the time included with the
timestamp token or the time mark and thus the revocation
status information should be captured after the end of the
grace period.
C.4.1.1 CRL information
When using CRLs to get revocation information, a verifier will have to
make sure that he or she gets at the time of the first verification the
appropriate certificate revocation information from the signer's CA.
This should be done as soon as possible to minimize the time delay
between the generation and verification of the signature. However, a
"grace period" is required to allow CAs time to process revocation
requests.
For example, a revocation request may arrive at a CA just before
issuing the next CRL and there may not enough time to include the
revised revocation status information. This involves checking that the
signer certificate serial number is not included in the CRL. The
signer, the initial or subsequent verifier may obtain either this CRL.
If obtained by the signer, then it shall be conveyed to the verifier.
It may be convenient to archive the CRL for ease of subsequent
verification or arbitration. Alternatively, provided the CRL is
archived elsewhere which is accessible for the purpose of arbitration,
then the serial number of the CRL used may be archived together with
the verified electronic signature as an CAdES-C form.
Even if the certificate serial number appears in the CRL with the
status "suspended" (i.e. on hold), the signature is not to be deemed as
valid since a suspended certificate is not supposed to be used even by
its rightful owner.
C.4.1.2 OCSP information
When using OCSP to get revocation information, a verifier will have to
make sure that he or she gets at the time of the first verification an
OCSP response that contains the status "valid". This should be done as
soon as possible after the generation of the signature, still providing
a "grace period" suitable enough to allow the involved authority to
process a "last minute" revocation request The signer, the verifier or
any other third party may fetch this OCSP response. Since OCSP
responses are transient and thus are not archived by any TSP including
CA, it is the responsibility of every verifier to make sure that it is
stored in a safe place. The simplest way is to store them associated
with the electronic signature. An alternative would be to store them
in some storage so that they can then be easily retrieved, and
incorporate references to them in the electronic signature itself as an
CAdES-C form.
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In the same way as for the case of the CRL, it may happen that the
certificate is declared as invalid but with the secondary status
"suspended". In such a case, same comment as for CRL applies.
C.4.2 Certification path
A verifier may have to ascertain that the certification path was valid,
at the time of the signature, up to a trust point according to the:
- naming constraints;
- certificate policy constraints;
- Signature Policy, when applicable.
Since the time of the signature cannot be known with certainty, an
upper limit of it should be used as indicated by either the time stamp
or time mark.
In this case it will be necessary to capture all the certificates from
the certification path, starting with those from the signer and ending
up with those of the self-signed certificate from one trusted root,
when applicable this may be specified as part of the Signature Policy.
In addition, it will be necessary to capture the Certificate Authority
Revocation Lists (CARLs) to prove than none of the CAs from the chain
was revoked at the time of the signature. Again, all this material may
be incorporated in the electronic signature (ES X forms). An
alternative would be to store it in some storage so that they can it be
easily retrieved, and incorporate references to it in the electronic
signature itself as an CAdES-C form.
C.4.3 Time-stamping for long life of signatures
An important property for long standing signatures is that a signature,
having been found once to be valid, shall continue to be so months or
years later.
A signer, verifier or both may be required to provide on request, proof
that a digital signature was created or verified during the validity
period of the all the certificates that make up the certificate path.
In this case, the signer, verifier or both will also be required to
provide proof that the signer's certificate and all the CA certificates
used to form a valid certification path were not revoked when the
signature was created or verified.
It would be quite unacceptable, to consider a signature as invalid even
if the keys or certificates were later compromised. Thus there is a
need to be able to demonstrate that the signature keys was valid at the
time that the signature was created to provide long term evidence of
the validity of a signature.
It could be the case that a certificate was valid at the time of the
signature but revoked some time later. In this event, evidence shall
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be provided that the document was signed before the signing key was
revoked. Time-stamping by a Time-Stamping Authority (TSA) can provide
such evidence. A time stamp is obtained by sending the hash value of
the given data to the TSA. The returned "time-stamp" is a signed
document that contains the hash value, the identity of the TSA, and the
time of stamping. This proves that the given data existed before the
time of stamping. Time-stamping a digital signature (by sending a hash
of the signature to the TSA) before the revocation of the signer's
private key, provides evidence that the signature has been created
before the key was revoked.
If a recipient wants to hold a valid electronic signature he will have
to ensure that he has obtained a valid time stamp for it, before that
key (and any key involved in the validation) is revoked. The sooner
the time-stamp is obtained after the signing time, the better. Any
time stamp or time mark that is taken after the expiration date of any
certificate in the certification path has no value in proving the
validity of a signature.
It is important to note that signatures may be generated "off-line" and
time-stamped at a later time by anyone, for example by the signer or
any recipient interested in the value of the signature. The time stamp
can thus be provided by the signer together with the signed document,
or obtained by the recipient following receipt of the signed document.
The time stamp is NOT a component of the Basic Electronic Signature,
but the essential component of the ES with Time-stamp.
It is required in the present document that if a signer's digital
signature value is to be time-stamped, the Time-Stamp Token is issued
by a trusted source, known as a Time-stamping Authority.
The present document requires that the signer's digital signature value
is time-stamped by a trusted source before the electronic signature can
become an ES with Complete validation data. Acceptable TSAs may be
specified in a Signature Validation Policy.
This technique is referred to as CAdES-C in the present document.
Should both the signer and verifier be required to time-stamp the
signature value to meet the requirements of the signature policy, the
signature policy MAY specify a permitted time delay between the two
time stamps.
C.4.4 Time-stamping for long life of signature before CA key
compromises
Time-stamped extended electronic signatures are needed when there is a
requirement to safeguard against the possibility of a CA key in the
certificate chain ever being compromised. A verifier may be required
to provide on request, proof that the certification path and the
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revocation information used a the time of the signature were valid,
even in the case where one of the issuing keys or OCSP responder keys
is later compromised.
The present document defines two ways of using time-stamps to protect
against this compromise:
- time-stamp the ES with Complete validation data, when an OCSP
response is used to get the status of the certificate from the
signer (CAdES-X Type 1). This format is suitable to be used with
an OCSP response and offers the additional advantage to provide
an integrity protection over the whole data;
- time-stamp only the certification path and revocation information
references when a CRL is used to get the status of the
certificate from the signer (CAdES-X Type2). This format is
suitable to be used with CRLs, since the time-stamped information
may be used for more than one signature (when signers have their
certificates issued by the same CA and when signatures can be
checked using the same CRLs).
NOTE: The signer, verifier or both may obtain the time-stamp.
C.4.4.1 Time-stamping the ES with complete validation data
(CAdES-X Type 1)
When an OCSP response is used, it is necessary to time stamp in
particular that response in the case the key from the responder would
be compromised. Since the information contained in the OCSP response
is user specific and time specific, an individual time stamp is needed
for every signature received. Instead of placing the time stamp only
over the certification path references and the revocation information
references, which include the OCSP response, the time stamp is placed
on the CAdES-C. Since the certification path and revocation
information references are included in the ES with Complete validation
data they are also protected. For the same cryptographic price, this
provides an integrity mechanism over the ES with Complete validation
data. Any modification can be immediately detected. It should be
noticed that other means of protecting/detecting the integrity of the
ES with Complete Validation Data exist and could be used.
Although the technique requires a time stamp for every signature, it is
well suited for individual users wishing to have an integrity protected
copy of all the validated signatures they have received.
By time-stamping the complete electronic signature, including the
digital signature as well as the references to the certificates and
revocation status information used to support validation of that
signature, the time-stamp ensures that there is no ambiguity in the
means of validating that signature.
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This technique is referred to as CAdES-X Type 1 in the present
document.
NOTE: Trust is achieved in the references by including a hash of the
data being referenced.
If it is desired for any reason to keep a copy of the additional data
being referenced, the additional data may be attached to the electronic
signature, in which case the electronic signature becomes an CAdES-X
Long Type 1 as defined by the present document.
An CAdES-X Long Type 1 is simply the concatenation of an CAdES-X Type 1
with a copy of the additional data being referenced.
C.4.4.2 Time-stamping certificates and revocation information
references (CAdES-X Type 2)
Time-stamping each ES with Complete Validation Data as defined above
may not be efficient, particularly when the same set of CA certificates
and CRL information is used to validate many signatures.
Time-stamping CA certificates will stop any attacker from issuing bogus
CA certificates that could be claimed to exist before the CA key was
compromised. Any bogus time-stamped CA certificates will show that the
certificate was created after the legitimate CA key was compromised.
In the same way, time-stamping CA CRLs, will stop any attacker from
issuing bogus CA CRLs which could be claimed to exist before the CA key
was compromised.
Time-stamping of commonly used certificates and CRLs can be done
centrally, e.g. inside a company or by a service provider. This method
reduces the amount of data the verifier has to time-stamp, for example
it could reduce to just one time stamp per day (i.e. in the case were
all the signers use the same CA and the CRL applies for the whole day).
The information that needs to be time stamped is not the actual
certificates and CRLs but the unambiguous references to those
certificates and CRLs.
This technique is referred to as CAdES-X Type 2 in the present document
and requires the following:
- all the CA certificates references and revocation information
references (i.e. CRLs) used in validating the CAdES-C are covered
by one or more time-stamp.
Thus an CAdES-C with a time-stamp signature value at time T1, can be
proved valid if all the CA and CRL references are time-stamped at time
T1+.
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C.4.5 Time-stamping for archive of signature
Advances in computing increase the probability of being able to break
algorithms and compromise keys. There is therefore a requirement to be
able to protect electronic signatures against this possibility.
Over a period of time weaknesses may occur in the cryptographic
algorithms used to create an electronic signature (e.g. due to the time
available for crypto analysis, or improvements in crypto analytical
techniques). Before such weaknesses become likely, a verifier should
take extra measures to maintain the validity of the electronic
signature. Several techniques could be used to achieve this goal
depending on the nature of the weakened cryptography. In order to
simplify matters, a single technique, called Archive validation data,
covering all the cases is being used in the present document.
Archive validation data consists of the validation data and the
complete certificate and revocation data, time stamped together with
the electronic signature. The Archive validation data is necessary if
the hash function and the crypto algorithms that were used to create
the signature are no longer secure. Also, if it cannot be assumed that
the hash function used by the Time Stamping Authority is secure, then
nested time-stamps of Archived Electronic Signature are required.
The potential for Trusted Service Provider (TSP) key compromise should
be significantly lower than user keys, because TSP(s) are expected to
use stronger cryptography and better key protection. It can be
expected that new algorithms (or old ones with greater key lengths)
will be used. In such a case, a sequence of time-stamps will protect
against forgery. Each time-stamp needs to be affixed before either the
compromise of the signing key or of the cracking of the algorithms used
by the TSA. TSAs (Time-stamping Authorities) should have long keys
(e.g. which at the time of drafting the present document was at least
2048 bits for the signing RSA algorithm) and/or a "good" or different
algorithm.
Nested time-stamps will also protect the verifier against key
compromise or cracking the algorithm on the old electronic signatures.
The process will need to be performed and iterated before the
cryptographic algorithms used for generating the previous time stamp
are no longer secure. Archive validation data may thus bear multiple
embedded time stamps.
This technique is referred to as CAdES-A in the present document.
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C.4.6 Reference to additional data
Using CAdES-X Type 1 or CAdES-X Type 2 extended validation data
verifiers still needs to keep track of all the components that were
used to validate the signature, in order to be able to retrieve them
again later on. These components may be archived by an external source
like a trusted service provider, in which case referenced information
that is provided as part of the ES with Complete validation data
(CAdES-C) is adequate. The actual certificates and CRL information
reference in the CAdES-C can be gathered when needed for arbitration.
If references to additional data are not adequate, then the actual
values of all the certificates and revocation information required may
be part of the electronic signature. This technique is referred to as
CAdES-X Long Type 1 or CAdES-X Long Type 2 in the present document.
C.4.7 Time-stamping for mutual recognition
In some business scenarios both the signer and the verifier need to
time-stamp their own copy of the signature value. Ideally the two
time-stamps should be as close as possible to each other.
EXAMPLE: A contract is signed by two parties A and B representing
their respective organizations, to time-stamp the signer
and verifier data two approaches are possible:
- under the terms of the contract pre-defined common
"trusted" TSA may be used;
- if both organizations run their own time-stamping
services, A and B can have the transaction
time-stamped by these two time-stamping services.
In the latter case, the electronic signature will only be considered as
valid, if both time-stamps were obtained in due time (i.e. there should
not be a long delay between obtaining the two time-stamps). Thus,
neither A nor B can repudiate the signing time indicated by their own
time-stamping service. Therefore, A and B do not need to agree on a
common "trusted" TSA to get a valid transaction.
It is important to note that signatures may be generated "off-line" and
time-stamped at a later time by anyone, e.g. by the signer or any
recipient interested in validating the signature. The time-stamp over
the signature from the signer can thus be provided by the signer
together with the signed document, and/or obtained by the verifier
following receipt of the signed document.
The business scenarios may thus dictate that one or more of the long-
term signature time-stamping methods describe above be used. This may
be part of a mutually agreed Signature Validation Policy which is part
of an agreed signature policy under which digital signature may be used
to support the business relationship between the two parties.
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C.4.8 TSA key compromise
TSA servers should be built in such a way that once the private
signature key is installed, there is minimal likelihood of compromise
over as long as possible period. Thus the validity period for the
TSA's keys should be as long as possible.
Both the CAdES-T and the CAdES-C contain at least one time stamp over
the signer's signature. In order to protect against the compromise of
the private signature key used to produce that time-stamp, the Archive
validation data can be used when a different Time-Stamping Authority
key is involved to produce the additional time-stamp. If it is
believed that the TSA key used in providing an earlier time-stamp may
ever be compromised (e.g. outside its validity period), then the CAdES-
A should be used. For extremely long periods this may be applied
repeatedly using new TSA keys.
This technique is referred to as a nested CAdES-A in the present
document.
C.5 Multiple signatures
Some electronic signatures may only be valid if they bear more than one
signature. This is the case generally when a contract is signed
between two parties. The ordering of the signatures may or may not be
important, i.e. one may or may not need to be applied before the other.
Several forms of multiple and counter signatures need to be supported,
which fall into two basic categories:
- independent signatures;
- embedded signatures.
Independent signatures are parallel signatures where the ordering of
the signatures is not important. The capability to have more than one
independent signature over the same data shall be provided.
Embedded signatures are applied one after the other and are used where
the order the signatures are applied is important. The capability to
sign over signed data shall be provided.
These forms are described in clause 5.13. All other multiple signature
schemes, e.g. a signed document with a countersignature, double
countersignatures or multiple signatures, can be reduced to one or more
occurrence of the above two cases.
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Annex D (informative):Data protocols to interoperate with TSPs
D.1 Operational protocols
The following protocols can be used by signers and verifiers to
interoperate with Trusted Service Providers during the electronic
signature creation and validation.
D.1.1 Certificate retrieval
User certificates, CA certificate and cross-certificates can be
retrieved from a repository using the Lightweight Directory Access
Protocol as defined in as defined RFC 2559 (see informative
references), with the schema defined in RFC 2587 (see informative
references).
D.1.2 CRL retrieval
Certificate revocation lists, including authority revocation lists and
partial CRL variants, can be retrieved from a repository using the
Lightweight Directory Access Protocol as defined in RFC 2559 (see
informative references), with the schema defined in RFC 2587 (see
informative references).
D.1.3 OnLine certificate status
As an alternative to use of certificate revocation lists the status of
certificate can be checked using the OnLine Certificate Status Protocol
(OCSP) as defined in RFC 2560 [3].
D.1.4 Time-stamping
The time-stamping service can be accessed using the Time-Stamping
Protocol defined in RFC 3161 [7].
D.2 Management protocols
Signers and verifiers can use the following management protocols to
manage the use of certificates.
D.2.1 Request for certificate revocation
Request for a certificate to be revoked can be made using the
revocation request and response messages defined in
RFC 2510 (see informative references).
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Annex E (informative): Guidance on naming
E.1 Allocation of names
The subject name shall be allocated through a registration scheme
administered through a Registration Authority (RA) to ensure
uniqueness. This RA may be an independent body or a function carried
out by the Certification Authority.
In addition to ensuring uniqueness, the RA shall verify that the name
allocated properly identifies the applicant and that authentication
checks are carried out to protect against masquerade.
The name allocated by an RA is based on registration information
provided by, or relating to, the applicant (e.g. his personal name,
date of birth, residence address) and information allocated by the RA.
Three variations commonly exist:
- the name is based entirely on registration information which
uniquely identifies the applicant (e.g. "Pierre Durand (born on)
July 6, 1956");
- the name is based on registration information with the addition
of qualifiers added by the registration authority to ensure
uniqueness (e.g. "Pierre Durand 12");
- the registration information is kept private by the registration
authority and the registration authority allocates a "pseudonym".
E.2 Providing access to registration information
Under certain circumstances it may be necessary for information used
during registration, but not published in the certificate, to be made
available to third parties (e.g. to an arbitrator to resolve a dispute
or for law enforcement). This registration information is likely to
include personal and sensitive information.
Thus the RA needs to establish a policy for:
- whether the registration information should be disclosed;
- to whom such information should be disclosed;
- under what circumstances such information should be disclosed.
This policy may be different whether the RA is being used only within a
company or for public use. The policy will have to take into account
national legislation and in particular any data protection and privacy
legislation.
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Currently, the provision of access to registration is a local matter
for the RA. However, if open access is required, standard protocols
such as HTTP - RFC 2068 (Internet Web Access Protocol) may be employed
with the addition of security mechanisms necessary to meet the data
protection requirements (e.g. Transport Layer Security - RFC 2246 with
client authentication).
E.3 Naming schemes
E.3.1 Naming schemes for individual citizens
In some cases the subject name that is contained in a public key
certificate may not be meaningful enough. This may happen because of
the existence of homonyms or because of the use of pseudonyms. A
distinction could be made if more attributes were present. However,
adding more attributes to a public key certificate placed in a public
repository would be going against the privacy protection requirements.
In any case the Registration Authority will get information at the time
of registration but not all that information will be placed in the
certificate. In order to achieve a balance between these two opposite
requirements the hash values of some additional attributes can be
placed in a public key certificate. When the certificate owner
provides these additional attributes, then they can be verified. Using
biometrics attributes may unambiguously identify a person. Example of
biometrics attributes that can be used include: a picture or a manual
signature from the certificate owner.
NOTE: Using hash values protects privacy only if the possible inputs
are large enough. For example, using the hash of a person's
social security number is generally not sufficient since it
can easily be reversed.
A picture can be used if the verifier once met the person and later on
wants to verify that the certificate that he or she got relates to the
person whom was met. In such a case, at the first exchange the picture
is sent and the hash contained in the certificate may be used by the
verifier to verify that it is the right person. At the next exchange
the picture does not need to be sent again.
A manual signature may be used if a signed document has been received
beforehand. In such a case, at the first exchange the drawing of the
manual signature is sent and the hash contained in the certificate may
be used by the verifier to verify that it is the right manual
signature. At the next exchange the manual signature does not need to
be sent again.
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E.3.2 Naming schemes for employees of an organization
The name of an employee within an organization is likely to be some
combination of the name of the organization and the identifier of the
employee within that organization.
An organization name is usually a registered name, i.e. business or
trading name used in day to day business. This name is registered by a
Naming Authority, which guarantees that the organization's registered
name is unambiguous and cannot be confused with another organization.
In order to get more information about a given registered organization
name, it is necessary to go back to a publicly available directory
maintained by the Naming Authority.
The identifier may be a name or a pseudonym (e.g. a nickname or a
employee number). When it is a name, it is supposed to be descriptive
enough to unambiguously identify the person. When it is a pseudonym,
the certificate does not disclose the identity of the person. However
it ensures that the person has been correctly authenticated at the time
of registration and therefore may be eligible to some advantages
implicitly or explicitly obtained through the possession of the
certificate. In either case, however, this can be insufficient because
of the existence of homonyms.
Placing more attributes in the certificate may be one solution, for
example by giving the organization unit of the person or the name of a
city where the office is located. However the more information is
placed in the certificate the more problems arise if there is a change
in the organization structure or the place of work. So this may not be
the best solution. An alternative is to provide more attributes (like
the organization unit and the place of work) through access to a
directory maintained by the company. It is likely that at the time of
registration the Registration Authority got more information than what
was placed in the certificate, if such additional information is placed
in a repository accessible only to the organization.
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Annex F (informative): Example structured contents and MIME
F.1 General description
The signed content may be structured as using MIME (Multipurpose
Internet Mail Extensions - RFC 2045 [6]. Whilst the MIME structure was
initially developed for Internet e-mail, it has a number of features
which make it useful to provide a common structure for encoding a range
of electronic documents and other multi-media data (e.g. photographs,
video). These features include:
- it provides a means of signalling the type of "object" being
carried (e.g. text, image, ZIP file, application data);
- it provides a means of associating a file name with an object;
- it can associate several independent "objects" (e.g. a document
and image) to form a multi-part object;
- it can handle data encoded in text or binary and, if necessary,
re-encode the binary as text.
When encoding a single object MIME consists of:
- header information, followed by;
- encoded content.
This structure can be extended to support multi-part content.
F.2 Header information
A MIME header includes:
MIME Version information:
e.g.: MIME-Version: 1.0
Content type information which includes information describing the
content sufficient for it to presented to a user or application process
as required. This includes information on the "media type" (e.g. text,
image, audio) or whether the data is for passing to a particular type
of application. In the case of text the content type includes
information on the character set used.
e.g. Content-Type: text/plain; charset="us-ascii"
Content encoding information, which defines how the content is encoded.
(See below about encoding supported by MIME).
Other information about the content such as a description, or an
associated file name.
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An example MIME header for text object is:
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable
An example MIME header for a binary file containing a word document is:
Content-Type: application/octet-stream
Content-Transfer-Encoding: base64
Content-Description: JCFV201.doc (Microsoft Word Document)
Content-Disposition: filename="JCFV201.doc"
F.3 Content encoding
MIME supports a range of mechanisms for encoding the both text and
binary data.
Text data can be carried transparently as lines of text data encoded in
7 or 8 bit ASCII characters. MIME also includes a "quoted-printable"
encoding which converts characters other than the basic ASCII into an
ASCII sequence.
Binary can either be carried:
- transparently a 8 bit octets; or
- converted to a basic set of characters using a system called
Base64.
NOTE: As there are some mail relays which can only handle 7 bit
ASCII, Base64 encoding is usually used on the Internet.
F.4 Multi-part content
Several objects (e.g. text and a file attachment) can be associated
together using a special "multi-part" content type. This is indicated
by the content type "multipart" with an indication of the string to be
used indicate a separation between each part.
In addition to a header for the overall multipart content, each part
includes its own header information indicating the inner content type
and encoding.
An example of a multipart content is:
Mime-Version: 1.0
Content-Type: multipart/mixed; boundary="----
=_NextPart_000_01BC4599.98004A80"
Content-Transfer-Encoding: 7bit
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------=_NextPart_000_01BC4599.98004A80
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Per your request, I've attached our proposal for the Java Card Version
2.0 API and the Java Card FAQ.
------=_NextPart_000_01BC4599.98004A80
Content-Type: application/octet-stream; name="JCFV201.doc"
Content-Transfer-Encoding: base64
Content-Description: JCFV201.doc (Microsoft Word Document)
Content-Disposition: attachment; filename="JCFV201.doc"
0M8R4KGxGuEAAAAAAAAAAAAAAAAAAAAAPgADAP7/CQAGAAAAAAAAAAAAAAACAAAAAgAAAAA
AAAAAEAAAtAAAAAEAAAD+////AAAAAAMAAAAGAAAA//////////////////////////////
//////////AANhAAQAYg==
------=_NextPart_000_01BC4599.98004A80--
Multipart content can be nested. So a set of associated objects (e.g.
HTML text and images) can be handled as a single attachment to another
object (e.g. text).
F.5 S/MIME
Previous clauses in this annex have described the use of MIME to encode
data. MIME encoded data can be signed (i.e. carried in the eContent of
the SignedData structure) thereby signalling the type of information
that has been signed.
MIME can also be used to encode the CMS structure containing data after
it has been signed so that, for example, this can be carried within an
e-mail message. The specific use of MIME to carry CMS (extended as
defined in the present document) secured data is called S/MIME. The
relationship between the general use of MIME for encoding content, CMS
and S/MIME is illustrated in figure F.1.
+------------++-------------++----------++------------++------------+
| || || || || |
| E-mail || S/MIME || CAdES || MIME || Word file |
| || || || || |
|From: Smith ||Content Type=||SignedData||ContentType=||Dear MrSmith|
|To:Jones ||application/ || Econtent ||application/||Received |
|Subject: ||pkcs7 || ||octet-stream|| 100 tins |
|Signed doc. || || || || |
| /| || /| || /| || /| || Mr.Jones |
| / -----+ / -----+ / -----+ / -----+ |
| \ -----+ \ -----+ \ -----+ \ -----+ |
| \| || \| || \| || \| || |
| |+------------- | |+------------+| |
+------------+ ++----------+ +------------+
Figure F.1
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S/MIME carries electronic signatures as either:
- an "application/pkcs7-mime" object with the CMS carried as binary
attachment (PKCS7 is the name of the early version of CMS).
An example of signed data encoded using this approach is:
Content-Type: application/pkcs7-mime; smime-type=signed-data;
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=smime.p7m
567GhIGfHfYT6ghyHhHUujpfyF4f8HHGTrfvhJhjH776tbB9HG4VQbnj7
77n8HHGT9HG4VQpfyF467GhIGfHfYT6rfvbnj756tbBghyHhHUujhJhjH
HUujhJh4VQpfyF467GhIGfHfYGTrfvbnjT6jH7756tbB9H7n8HHGghyHh
6YT64V0GhIGfHfQbnj75
This approach is similar to handling signed data as any other binary
file attachment. Thus, this encoding can be used where signed data
passes through gateways to other e-mail systems (e.g. those based on
other e-mail systems).
A "multipart/signed" object with the signed data and the signature
encoded as separate MIME objects.
An example of signed data encoded this approach is:
Content-Type: multipart/signed;
protocol="application/pkcs7-signature";
micalg=sha1; boundary=boundary42
--boundary42
Content-Type: text/plain
This is a clear-signed message.
--boundary42
Content-Type: application/pkcs7-signature; name=smime.p7s
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=smime.p7s
ghyHhHUujhJhjH77n8HHGTrfvbnj756tbB9HG4VQpfyF467GhIGfHfYT6
4VQpfyF467GhIGfHfYT6jH77n8HHGghyHhHUujhJh756tbB9HGTrfvbnj
n8HHGTrfvhJhjH776tbB9HG4VQbnj7567GhIGfHfYT6ghyHhHUujpfyF4
7GhIGfHfYT64VQbnj756
--boundary42--
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With this second approach MIME the signed data passes through the CMS
process and is carried as part of the S/MIME structure as illustrated
in figure F.2. The CMS structure just holds the electronic signature.
+------------++-------------++----------++------------++------------+
| || || || || |
| E-mail || | /MIME || CAdES || MIME || Word file |
| || || || || |
|From: Smith ||Content Type=||SignedData||ContentType=||Dear MrSmith|
|To:Jones ||multipart/ || ||application/||Received |
|Subject: ||signed || ||octet-stream|| 100 tins |
|Signed doc. || /| || || || |
| /| || / -----------------+ /| || Mr.Jones |
| / -----+ \ -----------------+ / -----+ |
| \ -----+ \| || || \ -----+ |
| \| ||ContentType= || || \| || |
+------------+|application/ || |+------------+| |
|octet-stream || | +------------+
| || |
|ContentType= || |
|application/ || |
|pkcs7- || |
|signature || |
| /| || |
| / -----+ |
| \ -----+ |
| \| ||----------+
| |
+-------------+
Figure F.2
The second approach (multipart/signed) has the advantage that the
signed data can be decoded by any MIME compatible e-mail system even if
it does not recognize CMS encoded electronic signatures. However, this
form cannot be used with other e-mail systems.
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Annex G (informative): Relationship to the European Directive and EESSI
G.1 Introduction
This annex provides an indication of the relationship between
electronic signatures created under the present document and
requirements under the European Parliament and Council Directive on a
Community framework for electronic signatures.
NOTE: Legal advice should be sought on the specific national
legislation regarding use of electronic signatures.
The present document is one of a set of standards being defined under
the "European Electronic Signature Standardization Initiative" (EESSI)
for electronic signature products and solutions compliant with the
European Directive for electronic signatures.
G.2 Electronic signatures and the directive
This directive defines electronic signatures as:
- "data in electronic form which are attached to or logically
associated with other electronic data and which serve as a method
of authentication".
The directive states that an electronic signature should not be denied
"legal effectiveness and admissibility as evidence in legal
proceedings" solely on the grounds that it is in electronic form.
The directive identifies an electronic signature as having equivalence
to a hand-written signature if it meets specific criteria:
- it is an "advanced electronic signature" with the following
properties:
a) it is uniquely linked to the signatory;
b) it is capable of identifying the signatory;
c) it is created using means that the signatory can maintain
under his sole control; and
d) it is linked to the data to which it relates in such a
manner that any subsequent change of the data is detectable.
- it is based on a certificate which meets detailed criteria given
in annex I to the directive and is issued by a "certification-
service-provider" which meets requirements given in annex II to
the directive. Such a certificate is referred to as a "qualified
certificate";
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- it is created by a "device" which detailed criteria given in
annex III to the directive. Such a device is referred to a
"secure-signature-creation device";
This form of electronic signature is referred to as a "qualified
electronic signature" in EESSI (see below).
G.3 ETSI electronic signature formats and the directive
An electronic signature created in accordance with the present document
is:
a) considered to be an "electronic signature" under the terms of
the Directive;
b) considered to be an "advanced electronic signature" under the
terms of the Directive;
c) considered to be a "Qualified Electronic Signature" provided the
additional requirements in annex I, II and III of the Directive
are met. The requirements in annex I, II and III of the
Directive are outside the scope of the present document, and are
subject to further standardization.
G.4 EESSI standards and classes of electronic signature
G.4.1 Structure of EESSI standardization
EESSI looks at standards in several areas. See the ETSI ESI and CEN
web sites for the latest list of standards and their versions
- use of X.509 public key certificates as qualified certificates;
- security Management and Certificate Policy for CSPs Issuing
Qualified Certificates;
- security requirements for trustworthy systems used by CSPs
Issuing Qualified Certificates;
- security requirements for Secure Signature Creation Devices;
- security requirements for Signature Creation Systems;
- procedures for Electronic Signature Verification;
- electronic signature syntax and encoding formats;
- protocol to interoperate with a Time Stamping Authority;
- Policy requirements for Time-Stamping Authorities;
- XML electronic signature formats.
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Each of these standards addresses a range of requirements including the
requirements of Qualified Electronic Signatures as specified in article
5.1 of the Directive. However, some of them also address general
requirements of electronic signatures for business and electronic
commerce which all fall into the category of article 5.2 of the
Directive. Such variation in the requirements may be identified either
as different levels or different options.
G.4.2 Classes of electronic signatures
Since some of these standards address a range of requirements, it may
be useful to identify a set of standards to address a specific business
need. Such a set of standards and their uses defines a class of
electronic signature. The first class already identified is the
qualified electronic signature, fulfilling the requirements of article
5.1 of the Directive.
A limited number of "classes of electronic signatures" and
corresponding profiles could be defined by EESSI, in close co-operation
with actors on the market (business, users, suppliers). Need for such
standards is envisaged, in addition to those for qualified electronic
signatures, in areas such as:
- different classes of electronic signatures with long term
validity;
- electronic signatures for business transactions with limited
value.
G.4.3 EESSI classes and the ETSI electronic signature format
The electronic signature format defined in the present document is
applicable to the EESSI area "electronic signature and encoding
formats".
An electronic signature produced by a signer (see clause 5 and
conformance clause 10.1) is applicable to the proposed class of
electronic signature: "qualified electronic signatures fulfilling
article 5.1".
With the addition of validation data by the verifier (see clause 6 and
conformance clause 10.2) this would become applicable electronic
signatures adding long-term validity attributes to the qualified
electronic signature.
Annex H (informative):APIs for the generation and verification of
electronic signatures tokens
While the present document describes the data format of an electronic
signature, the question is whether there exists APIs (Application
Programming Interfaces) able to manipulate these structures. At least
two such APIs have been defined. One set by the IETF and another set
by the OMG (Object Management Group).
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H.1 Data framing
In order to be able to use either of these APIs, it will be necessary
to frame the previously defined electronic signature data structures
using a mechanism-independent token format. Clause 3.1 of RFC 2743
(see informative references) describes that framing incorporating an
identifier of the mechanism type to be used and enabling tokens to be
interpreted unambiguously.
In order to be processable by these APIs, all electronic signature data
formats that are defined in the present document shall be framed
following that description.
The encoding format for the token tag is derived from ASN.1 and DER,
but its concrete representation is defined directly in terms of octets
rather than at the ASN.1 level in order to facilitate interoperable
implementation without use of general ASN.1 processing code. The token
tag consists of the following elements, in order:
1) 0x60 -- Tag for RFC 2743 SEQUENCE; indicates that constructed
form, definite length encoding follows.
2) Token length octets, specifying length of subsequent data (i.e.
the summed lengths of elements 3 to 5 in this list, and of the
mechanism-defined token object following the tag). This element
comprises a variable number of octets:
a) If the indicated value is less than 128, it shall be
represented in a single octet with bit 8 (high order) set to
"0" and the remaining bits representing the value.
b) If the indicated value is 128 or more, it shall be represented
in two or more octets, with bit 8 of the first octet set to
"1" and the remaining bits of the first octet specifying the
number of additional octets. The subsequent octets carry the
value, 8 bits per octet, most significant digit first. The
minimum number of octets shall be used to encode the length
(i.e. no octets representing leading zeros shall be included
within the length encoding).
3) 0x06 -- Tag for OBJECT IDENTIFIER.
4) Object identifier length -- length (number of octets) of the
encoded object identifier contained in element 5, encoded per
rules as described in 2a) and 2b) above.
5) object identifier octets -- variable number of octets, encoded
per ASN.1 BER rules:
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- The first octet contains the sum of two values:
(1) the top-level object identifier component, multiplied by
40 (decimal); and
(2) the second-level object identifier component.
This special case is the only point within an object
identifier encoding where a single octet represents contents
of more than one component.
- Subsequent octets, if required, encode successively-lower
components in the represented object identifier. A
component's encoding may span multiple octets, encoding 7 bits
per octet (most significant bits first) and with bit 8 set to
"1" on all but the final octet in the component's encoding.
The minimum number of octets shall be used to encode each
component (i.e. no octets representing leading zeros shall be
included within a component's encoding).
NOTE: In many implementations, elements 3 to 5 may be stored and
referenced as a contiguous string constant.
The token tag is immediately followed by a mechanism-defined token
object. Note that no independent size specifier intervenes following
the object identifier value to indicate the size of the mechanism-
defined token object.
Tokens conforming to the present document shall have the following OID
in order to be processable by IDUP-APIs:
id-etsi-es-IDUP-Mechanism-v1 OBJECT IDENTIFIER ::=
{ itu-t(0) identified-organization(4) etsi(0)
electronic-signature-standard (1733) part1 (1) IDUPMechanism (4)
etsiESv1(1) }
H.2 IDUP-GSS-APIs defined by the IETF
The IETF CAT WG has produced in December 1998 an RFC (RFC 2479 - see
informative references) under the name of IDUP-GSS-API (Independent
Data Unit Protection) able to handle the electronic signature data
format defined in the present document.
The IDUP-GSS-API includes support for non-repudiation services.
It supports evidence generation, where "evidence" is information that
either by itself, or when used in conjunction with other information,
is used to establish proof about an event or action, as well a evidence
verification.
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IDUP supports various types of evidences. All the types defined in
IDUP are supported in the present document through the commitment type
parameter.
Clause 2.3.3 of IDUP describes the specific calls needed to handle
evidences ("EV" calls). The "EV" group of calls provides a simple,
high-level interface to underlying IDUP mechanisms when application
developers need to deal only with evidences but not with encryption or
integrity services.
All generations and verification are performed according to the content
of a NR policy that is referenced in the context.
Get_token_details is used to return to an application the attributes
that correspond to a given input token. Since IDUP-GSS- API tokens are
meant to be opaque to the calling application, this function allows the
application to determine information about the token without having to
violate the opaqueness intention of IDUP. Of primary importance is the
mechanism type, which the application can then use as input to the
IDUP_Establish_Env() call in order to establish the correct environment
in which to have the token processed.
Generate_token generates a non-repudiation token using the current
environment.
Verify_evidence verifies the evidence token using the current
environment. This operation returns a major_status code which can be
used to determine whether the evidence contained in a token is complete
(i.e. can be successfully verified (perhaps years) later). If a
token's evidence is not complete, the token can be passed to another
API: form_complete_pidu to complete it. This happens when a status
"conditionally valid" is returned. That status corresponds to the
status "validation incomplete" of the present document.
Form_complete_PIDU is used primarily when the evidence token itself
does not contain all the data required for its verification and it is
anticipated that some of the data not stored in the token may become
unavailable during the interval between generation of the evidence
token and verification unless it is stored in the token. The
Form_Complete_PIDU operation gathers the missing information and
includes it in the token so that verification can be guaranteed to be
possible at any future time.
H.3 CORBA security interfaces defined by the OMG
Non-repudiation interfaces have been defined in "CORBA Security", a
document produced by the OMG (Object Management Group). These
interfaces are described in IDL (Interface Definition Language) and are
optional.
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The handling of "tokens" supporting non-repudiation is done through the
following interfaces:
- set_NR_features specifies the features to apply to future
evidence generation and verification operations;
- get_NR_features returns the features which will be applied to
future evidence generation and verification operations;
- generate_token generates a Non-repudiation token using the
current Non-repudiation features;
- verify_evidence verifies the evidence token using the current
Non-repudiation features;
- get_tokens_details returns information about an input Non-
repudiation token. The information returned depends upon the
type of token;
- form_complete_evidence is used when the evidence token itself
does not contain all the data required for its verification, and
it is anticipated that some of the data not stored in the token
may become unavailable during the interval between generation of
the evidence token and verification unless it is stored in the
token. The form_complete_evidence operation gathers the missing
information and includes it in the token so that verification can
be guaranteed to be possible at any future time.
NOTE: The similarity between the two sets of APIs is noticeable.
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Annex I (informative):Cryptographic algorithms
RFC 3370 [10] describes the conventions for using several cryptographic
algorithms with the Crytographic Message Syntax (CMS). Only the
hashing and signing algorithms are appropriate for use with the present
document.
Since the publication of RFC 3370 [10], MD5 has been broken. This
algorithm is no more considered as appropriate and has been deleted
from the list of algorithms.
I.1 Digest algorithms
I.1.1 SHA-1
The SHA-1 digest algorithm is defined in FIPS Pub 180-1. The algorithm
identifier for SHA-1 is:
sha-1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3) oiw(14)
secsig(3) algorithm(2) 26 }
The AlgorithmIdentifier parameters field is optional. If present, the
parameters field shall contain an ASN.1 NULL. Implementations should
accept SHA-1 AlgorithmIdentifiers with absent parameters as well as
NULL parameters. Implementations should generate SHA-1
AlgorithmIdentifiers with NULL parameters.
I.1.2 General
The following is a selection of work that has been done in the area of
digest algorithms or, as they are often called, hash functions:
- ISO/IEC 10118-1 (1994): "Information technology - Security
techniques - Hash-functions - Part 1: General". ISO/IEC 10118-1
contains definitions and describes basic concepts.
- ISO/IEC 10118-2 (1994): "Information technology - Security
techniques - Hash-functions - Part 2: Hash-functions using an n-
bit block cipher algorithm". ISO/IEC 10118-2 specifies two ways
to construct a hash-function from a block cipher.
- ISO/IEC 10118-3 (1997): "Information technology - Security
techniques - Hash-functions - Part 3: Dedicated hash-functions".
ISO/IEC 10118-3 specifies the following dedicated hash-functions:
- SHA-1 (FIPS 180-1);
- RIPEMD-128;
- RIPEMD-160.
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- ISO/IEC 10118-4 (1998): "Information technology - Security
techniques - Hash-functions - Part 4: Hash-functions using
modular arithmetic".
- RFC 1320 (PS 1992): "The MD4 Message-Digest Algorithm". RFC 1320
specifies the hash-function MD4. Today, MD4 is considered out-
dated.
- RFC 1321 (I 1992): "The MD5 Message-Digest Algorithm". RFC 1321
(informational) specifies the hash-unction MD5.
- FIPS Publication 180-1 (1995): "Secure Hash Standard". FIPS 180-1
specifies the Secure Hash Algorithm (SHA), dedicated hash-
function developed for use with the DSA. The original SHA
published in 1993 was slightly revised in 1995 and renamed SHA-1.
- ANSI X9.30-2 (1997): "Public Key Cryptography for the Financial
Services Industry - Part 2: The Secure Hash Algorithm (SHA-1)".
X9.30-2 specifies the ANSI-Version of SHA-1.
- ANSI X9.31-2 (1996): "Public Key Cryptography Using Reversible
Algorithms for the Financial Services Industry - Part 2: Hash
Algorithms". X9.31-2 specifies hash algorithms.
I.2 Digital signature algorithms
I.2.1 DSA
The DSA signature algorithm is defined in FIPS Pub 186. DSA is always
used with the SHA-1 message digest algorithm. The algorithm identifier
for DSA is:
id-dsa-with-sha1 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
x9-57 (10040) x9cm(4) 3 }
The AlgorithmIdentifier parameters field shall not be present.
I.2.2 RSA
The RSA signature algorithm is defined in RFC 2437 (see informative
references). RFC 3370 [10] specifies the use of the RSA signature
algorithm with the SHA-1 algorithm. The algorithm identifier for RSA
with SHA-1 is:
Sha1WithRSAEncryption OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs-1(1) 5 }
NOTE: RFC 3370 [10] recommends that MD5 is not used for new
implementations.
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I.2.3 General
The following is a selection of work that has been done in the area of
digital signature mechanisms:
- FIPS Publication 186 (1994): "Digital Signature Standard".
NIST's Digital Signature Algorithm (DSA) is a variant of
ElGamal's Discrete Logarithm based digital signature mechanism.
The DSA requires a 160-bit hash-function and mandates SHA-1.
- IEEE P1363 (2000): "Standard Specifications for Public-Key
Cryptography". IEEE P1363 contains mechanisms for digital
signatures, key establishment, and encipherment based on three
families of public-key schemes:
- "Conventional" Discrete Logarithm (DL) based techniques, i.e.
Diffie-Hellman (DH) key agreement, Menezes-Qu-Vanstone (MQV)
key agreement, the Digital Signature Algorithm (DSA), and
Nyberg-Rueppel (NR) digital signatures;
- Elliptic Curve (EC) based variants of the DL-mechanisms
specified above, i.e. EC-DH, EC-MQV, EC-DSA, and EC-NR. For
elliptic curves, implementation options include mod p and
characteristic 2 with polynomial or normal basis
representation;
- Integer Factoring (IF) based techniques including RSA
encryption, RSA digital signatures, and RSA-based key
transport.
- ISO/IEC 9796 (1991): "Information technology - Security
techniques - Digital signature scheme giving message recovery".
ISO/IEC 9796 specifies a digital signature mechanism based on the
RSA public-key technique and a specifically designed redundancy
function.
- ISO/IEC 9796-2 (1997): "Information technology - Security
techniques - Digital signature schemes giving message recovery -
Part 2: Mechanisms using a hash-function". ISO/IEC 9796-2
specifies digital signature mechanisms with partial message
recovery that are also based on the RSA technique but make use of
a hash-function.
- ISO/IEC 9796-4 (1998): "Digital signature schemes giving message
recovery - Part 4: Discrete logarithm based mechanisms". ISO/IEC
9796-4 specifies digital signature mechanisms with partial
message recovery that are based on Discrete Logarithm techniques.
The document includes the Nyberg-Rueppel scheme.
- ISO/IEC 14888-1: "Digital signatures with appendix - Part 1:
General". ISO/IEC 14888-1 contains definitions and describes the
basic concepts of digital signatures with appendix.
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- ISO/IEC 14888-2: "Digital signatures with appendix - Part 2:
Identity-based mechanisms". ISO/IEC 14888-2 specifies digital
signature schemes with appendix that make use of identity-based
keying material. The document includes the zero-knowledge
techniques of Fiat-Shamir and Guillou-Quisquater.
- ISO/IEC 14888-3: "Digital signatures with appendix - Part 3:
Certificate-based mechanisms". ISO/IEC 14888-3 specifies digital
signature schemes with appendix that make use of certificate-
based keying material. The document includes five schemes:
- DSA;
- EC-DSA, an elliptic curve based analog of NIST's Digital
Signature Algorithm;
- Pointcheval-Vaudeney signatures;
- RSA signatures;
- ESIGN.
- ISO/IEC 15946-2 (2002) : "Cryptographic techniques based on
elliptic curves - Part 2: Digital signatures".
- ISO/IEC 15946-3 (2002) specifies digital signature schemes with
appendix using elliptic curves.
- The document includes two schemes:
- EC-DSA, an elliptic curve based analog of NIST's Digital
Signature Algorithm;
- EC-AMV, an elliptic curve based analog of the Agnew-Muller-
Vanstone signature algorithm.
- ANSI X9.31-1 (1997): "Public Key Cryptography Using Reversible
Algorithms for the Financial Services Industry - Part 1: The RSA
Signature Algorithm". ANSI X9.31-1 specifies a digital signature
mechanism with appendix using the RSA public-key technique.
- ANSI X9.30-1 (1997): "Public Key Cryptography Using Irreversible
Algorithms for the Financial Services Industry - Part 1: The
Digital Signature Algorithm (DSA)". ANSI X9.30-1 specifies the
DSA, NIST's Digital Signature Algorithm.
- ANSI X9.62 (1998): "Public Key Cryptography for the Financial
Services Industry - The Elliptic Curve Digital Signature
Algorithm (ECDSA)". ANSI X9.62 specifies the Elliptic Curve
Digital Signature Algorithm, an analog of NIST's Digital
Signature Algorithm (DSA) using elliptic curves. The appendices
provide tutorial information on the underlying mathematics for
elliptic curve cryptography and many examples.
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Annex J (informative): Changes from the previous version
The title of the document has changed to be aligned with the title
of XAdES, the vocabulary used within the present document has been
aligned with the vocabulary used in XAdES,
In the previous version of TS 101 733 (i.e. version 1.5.1)
sigPolicyHash was mandatory. Implementations requiring to be
backward compatible with version 1.5.1 and previous versions
of the current document MUST include SigPolicyHash.
The OIDs from the ASN.1 modules have changed for the following
reasons:
- the OIDs of the ASN.1 modules of RFC 2560 and RFC 3161 have been
included.
- since RFC 2459 and RFC 3369 has been obsoleted by RFC 3280 and
RFC 3852 respectively, there was the need to refer to the OIDs
of the ASN.1 modules of RFC 3280 and RFC 3852, instead of the
OIDs of the ASN.1 modules of RFC 2459 and RFC 3369.
- the other change is related to the field sigPolicyHash from
SignaturePolicyId (see clause 5.8.1). That field was mandatory
and is now optional.
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Full Copyright Statement
Copyright (C) The Internet Society (2005).
The contents of this Informational RFC amounts to a transposition of
the ETSI TS 101 733 V.1.6.3 and is technically equivalent to it.
The ETSI TS is under the ETSI Copyright (C). Individual copies of
this ETSI deliverable can be downloaded from http://www.etsi.org.
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
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