Internet DRAFT - draft-santesson-svt-pdf
draft-santesson-svt-pdf
Network Working Group S. Santesson
Internet-Draft IDsec Solutions
Intended status: Informational R. Housley
Expires: 22 September 2022 Vigil Security
21 March 2022
PDF Signature Validation Token
draft-santesson-svt-pdf-03
Abstract
This document defines a PDF profile for the Signature Validation
Token defined in [SVT].
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. SVT in PDF Documents . . . . . . . . . . . . . . . . . . . . 3
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3.1. SVT Extension to Timestamp Tokens . . . . . . . . . . . . 3
4. SVT Claims . . . . . . . . . . . . . . . . . . . . . . . . . 3
4.1. Profile Identifer . . . . . . . . . . . . . . . . . . . . 3
4.2. Signature Reference Data . . . . . . . . . . . . . . . . 3
4.3. Signed Data Reference Data . . . . . . . . . . . . . . . 4
4.4. Signer Certificate References . . . . . . . . . . . . . . 4
5. JOSE Header . . . . . . . . . . . . . . . . . . . . . . . . . 4
5.1. SVT Signing Key Reference . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The "Signature Validation Token" specification [SVT] defines a basic
token to support signature validation in a way that can significantly
extend the lifetime of a signature.
This specification defines a profile for implementing SVT with a
signed PDF document, and defines the following aspects of SVT usage:
* How to include reference data related to PDF signatures and PDF
documents in an SVT.
* How to add an SVT token to a PDF document.
PDF document signatures are added as incremental updates to the
signed PDF document and signs all data of the PDF document up until
the current signature. When more than one signature is added to a
PDF document the previous signature is signed by the next signature
and can not be updated with additional data after this event.
To minimize the impact on PDF documents with multiple signatures and
to stay backwards compatible with PDF software that do not understand
SVT, PDF documents add one SVT token for all signatures of the PDF as
an extension to a document timestamp added to the signed PDF as an
incremental update. This SVT covers all signatures of the signed
PDF.
2. Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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The definitions in [SVT] apply also to this document.
3. SVT in PDF Documents
The SVT for a signed PDF document MAY provide signature validation
information about any of the present signatures in the PDF. The SVT
MUST contain a separate "sig" claim (Signature object) for each
signature on the PDF that is covered by the SVT.
An SVT added to a signed PDF document MUST be added to a document
timestamp accordance with ISO 32000-2:2017 [ISOPDF2].
The document timestamp contains an [RFC3161] timestamp token
(TSTInfo) in EncapsulatedContentInfo of the CMS signature. The SVT
MUST be added to the timestamp token (TSTInfo) as an Extension object
as defined in Section 3.1.
3.1. SVT Extension to Timestamp Tokens
The SVT extension is an Extension suitable to be included in TSTInfo
as defined by [RFC3161].
The SVT extension is identified by the Object Identifier (OID)
1.2.752.201.5.2
Editors note: This is the current used OID. Consider assigning an
IETF extension OID.
This extension data (OCTET STRING) holds the bytes of SVT JWT,
represented as a UTF-8 encoded string.
This extension MUST NOT be marked critical.
Note: Extensions in timestamp tokens according to [RFC3161] are
imported from the definition of the X.509 certificate extensions
defined in [RFC5280].
4. SVT Claims
4.1. Profile Identifer
When this profile is used the SigValidation object MUST contain a
"profile" claim with the value "PDF".
4.2. Signature Reference Data
The SVT Signature object MUST contain a "sig_ref" claim (SigReference
object) with the following elements:
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* "id" -- Absent or a Null value.
* "sig_hash" -- The hash over the signature value bytes.
* "sb_hash" -- The hash over the DER encoded SignedAttributes in
SignerInfo.
4.3. Signed Data Reference Data
The SVT Signature object MUST contain one instance of the "sig_data"
claim (SignedData object) with the following elements:
* "ref" -- The string representation of the ByteRange value of the
PDF signature dictionary of the target signature. This is a
sequence of integers separated by space where each integer pair
specifies the start index and length of a byte range.
* "hash" -- The hash of all bytes identified by the ByteRange value.
This is the concatenation of all byte ranges identified by the
ByteRange value.
4.4. Signer Certificate References
The SVT Signature object MUST contain a "signer_cert_ref" claim
(CertReference object). The "type" parameter of the
"signer_cert_ref" claim MUST be either "chain" or "chain_hash".
* The "chain" type MUST be used when signature validation was
performed using one or more certificates where some or all of the
certificates in the chain are not present in the target signature.
* The "chain_hash" type MUST be used when signature validation was
performed using one or more certificates where all of the
certificates are present in the target signature.
Note: The referenced signer certificate MUST match any certificates
referenced using ESSCertID or ESSCertIDv2 from [RFC5035].
5. JOSE Header
5.1. SVT Signing Key Reference
The SVT JOSE header must contain one of the following header
parameters in accordance with [RFC7515], for storing a reference to
the public key used to verify the signature on the SVT:
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* "x5c" -- Holds an X.509 certificate [RFC5280] or a chain of
certificates. The certificate holding the public key that
verifies the signature on the SVT MUST be the first certificate in
the chain.
* "kid" -- A key identifier holding the Base64 encoded hash value of
the certificate that can verify the signature on the SVT. The
hash algorithm MUST be the same hash algorithm used when signing
the SVT as specified by the alg header parameter. The referenced
certificate SHOULD be the same certificate that was used to sign
the document timestamp that contains the SVT.
6. IANA Considerations
This document has no IANA actions.
7. Security Considerations
The security considerations of [SVT] applies also to this document.
8. Normative References
[ISOPDF2] ISO, "Document management -- Portable document format --
Part 2: PDF 2.0", ISO 32000-2, July 2017.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3161] Adams, C., Cain, P., Pinkas, D., and R. Zuccherato,
"Internet X.509 Public Key Infrastructure Time-Stamp
Protocol (TSP)", RFC 3161, DOI 10.17487/RFC3161, August
2001, <https://www.rfc-editor.org/info/rfc3161>.
[RFC5035] Schaad, J., "Enhanced Security Services (ESS) Update:
Adding CertID Algorithm Agility", RFC 5035,
DOI 10.17487/RFC5035, August 2007,
<https://www.rfc-editor.org/info/rfc5035>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
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[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <https://www.rfc-editor.org/info/rfc7515>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[SVT] Santesson, S. and R. Housley, "Signature Validation
Token", IETF draft-santesson-svt-02, September 2021.
Authors' Addresses
Stefan Santesson
IDsec Solutions AB
Forskningsbyn Ideon
SE-223 70 Lund
Sweden
Email: sts@aaa-sec.com
Russ Housley
Vigil Security, LLC
516 Dranesville Road
Herndon, VA, 20170
United States of America
Email: housley@vigilsec.com
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