Internet DRAFT - draft-ietf-lamps-key-attestation-ext
draft-ietf-lamps-key-attestation-ext
Limited Additional Mechanisms for PKIX and SMIME C. Wallace
Internet-Draft Red Hound
Intended status: Standards Track S. Turner
Expires: 20 April 2023 sn3rd
17 October 2022
Key Attestation Extension for Certificate Management Protocols
draft-ietf-lamps-key-attestation-ext-00
Abstract
Certification Authorities (CAs) issue certificates for public keys
conveyed to the CA via a certificate management message or protocol.
In some cases, a CA may wish to tailor certificate contents based on
whether the corresponding private key is secured by hardware in non-
exportable form. This document describes extensions that may be
included in any of several widely used certificate management
protocols to convey attestations about the private key to the CA to
support this determination.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-lamps-key-attestation-
ext/.
Discussion of this document takes place on the spasm Working Group
mailing list (mailto:spasm@ietf.org), which is archived at
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https://www.ietf.org/mailman/listinfo/spasm/.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
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This Internet-Draft will expire on 20 April 2023.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
3. Key Attestation Attribute or Extension . . . . . . . . . . . 4
3.1. Usage in PKCS #10 requests . . . . . . . . . . . . . . . 5
3.2. Usage in CRMF requests . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5.1. Key attestation extension object identifier . . . . . . . 6
5.2. Key attestation extension ASN.1 module object
identifier . . . . . . . . . . . . . . . . . . . . . . . 6
5.3. Attestation statement formats . . . . . . . . . . . . . . 6
5.3.1. WebAuthn Attestation Statement Format Identifiers for
Certificate Request Protocols . . . . . . . . . . . . 7
5.3.2. WebAuthn Extension Identifiers for Certificate Request
Protocols . . . . . . . . . . . . . . . . . . . . . . 9
6. ASN.1 Module . . . . . . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. Normative References . . . . . . . . . . . . . . . . . . 12
7.2. Informative References . . . . . . . . . . . . . . . . . 13
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
Many different certificate management protocols exist, including:
* PKCS #10 [RFC2986]
* Simple Certificate Enrolment Protocol (SCEP) [RFC8894]
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* Certificate Management over CMS (CMC) [RFC5272]
* Certificate Management Protocol (CMP) [RFC4210]
* Certificate Request Management Format (CRMF) [RFC4211]
* Enrollment over Secure Transport (EST) [RFC7030]
* Automatic Certificate Management Environment (ACME) [RFC8555]
Each of these specifications defines extensibility mechanisms to
customize requests sent to a Certification Authority (CA),
Registration Authority (RA), or certificate management server. This
document addresses the first six specifications in the above list, as
all can be customized using attributes or extensions. [RFC8555] is
somewhat different and is addressed by
[I-D.draft-bweeks-acme-device-attest].
Many operating system and device vendors offer functionality enabling
a device to generate a cryptographic attestation that can be used to
establish the provenance of a key:
* Android Key Attestation
(https://source.android.com/security/keystore/attestation)
* Trusted Platform Module (https://docs.microsoft.com/en-us/windows-
server/identity/ad-ds/manage/component-updates/tpm-key-
attestation)
* Apple Key Attestation
(https://developer.apple.com/documentation/devicecheck/
dcappattestservice/3573911-attestkey)
* Yubico PIV Attestation
(https://developers.yubico.com/PIV/Introduction/
PIV_attestation.html)
[WebAuthn] defines an "API enabling the creation and use of strong,
attested, scoped, public key-based credentials by web applications,
for the purpose of strongly authenticating users." In support of
this goal, it defines a model and corresponding formats to support
attestation functionality. Section 6.5 of [WebAuthn] describes the
general attestation structure and section 8 defines some specific
attestation formats. Similar to
[I-D.draft-bweeks-acme-device-attest], this specification uses the
attestation object definition from [WebAuthn] as a means of
supporting a variety of attestation formats, which are defined in the
IANA registry that was established by [RFC8809]; see [WebAuthnReg].
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This document defines a structure, KeyAttestation, that can be used
to convey a [WebAuthn] attestation statement as an attribute or
extension when using the protocols listed above.
2. Conventions and 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.
3. Key Attestation Attribute or Extension
A key attestation attribute or extension MAY be included in
certificate request messages to convey an attestation statement for
the private key corresponding to the public key contained in the
request. The attribute definition and the certificate extension
definition are exactly the same, and they are identified by the same
object identifier.
ext-keyAttestation EXTENSION ::= {
SYNTAX KeyAttestation IDENTIFIED BY id-pe-keyAttestation }
attr-keyAttestation ATTRIBUTE ::= {
SYNTAX KeyAttestation IDENTIFIED BY id-pe-keyAttestation }
id-pe-keyAttestation OBJECT IDENTIFIER ::= { id-pe TBD }
KeyAttestation ::= OCTET STRING
The KeyAttestation conveys an attestation statement as defined in
[WebAuthn] encoded as an OCTET STRING.
While the format of an attestation statement varies, all attestation
statement formats conveyed via a keyAttestation extension MUST
include the public key that is the subject of the corresponding
certificate management request. Certificate request messages that
contain a key attestation that does not include a public key or that
contain a public key that does not match the public key in the
certificate request SHOULD be rejected with no certificate issued,
however, a CA MAY elect to issue a certificate as if the request did
not contain a key attestation per local policy.
Some attestation statement formats support the use of challenge
password or nonce values. While the means of conveying challenge
password value or a nonce value to certificate request clients is
outside the scope of this document, each of SCEP [RFC8894], CMC
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[RFC5272], CMP [RFC4210] and EST [RFC7030] define means for conveying
nonce values to certificate request clients. In some cases,
challenge password or nonce values may be conveyed outside of a
certificate management protocol. For example, SCEP payloads in
Apple's Over-the-Air Profile Delivery and Configuration specification
[OTA] deliver challenge passwords in an XML-formatted set of
instructions.
Similarly, use and verification of a nonce value relative to an
attestation statement is outside the scope of this document.
Verification procedures for currently defined attestation statement
formats can be found in Section 8 of [WebAuthn]. Certificate request
messages that contain a key attestation that cannot be validated,
including processing any nonce or challenge password values, SHOULD
be rejected with no certificate issued, however, a CA MAY elect to
issue a certificate as if the request did not contain a key
attestation per local policy.
3.1. Usage in PKCS #10 requests
The PKCS #10 structure may be used directly or in SCEP, CMC, CMP or
EST contexts. Where PKCS #10 is used, the public key in the
attestation statement MUST match the public key in the
CertificationRequestInfo.subjectPKInfo field and the keyAttestation
attribute MUST appear in the CertificationRequestInfo.attributes
field.
3.2. Usage in CRMF requests
The CRMF structure may be used in CMC, CMP or EST. Where CRMF is
used, the public key in the attestation statement MUST match the
public key in the CertTemplate.publicKey field and the keyAttestation
extension MUST appear in the CertTemplate.extensions field.
4. Security Considerations
See Section 13 of [WebAuthn] for additional security considerations
related to attestation statement formats, including certificate
revocation.
CAs, RAs and certificate management servers will need a set of trust
anchors to validate attestation statements that may originate from
any number of sources. Where possible, a dedicated trust anchor and
issuing CA should be used when verifying a given type of attestation
statement. Where a trust anchor or issuing CA are shared for
mulitple sources of attestation statements, including constraints in
attestation signer certificates or attestation certificates is
recommended. [COTS] and [fido-metadata] define structures for
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conveying trust anchors that may be used for verifying attestations
such that constraints are implied or are explicitly stated.
Expression and validation of constraints imposed on trust anchors,
CAs or attestation signers is beyond the scope of this specification.
Key attestation statements may include a variety of information in
addition to the public key being attested. While not described in
this document, CAs, RAs and certificate management servers are free
to use any policy when evaluating this information. This evaluation
can result in rejection of a certificate request that features a
verifiable key attestation for the public key contained in the
request. For example, an attestation statement may indicate use of
an unacceptable firmware version.
5. IANA Considerations
5.1. Key attestation extension object identifier
An object identifier from the id-pe arc defined in [RFC7299] should
be assigned for id-pe-keyAttestation.
5.2. Key attestation extension ASN.1 module object identifier
An object identifier from the id-mod arc defined in [RFC7299] should
be assigned for id-mod-keyAttestation.
5.3. Attestation statement formats
Section 2.1 of [RFC8809] describes registration of new attestation
statement format types used when authenticating users via [WebAuthn].
This specification reuses the same format, but, because the context
for use is different, a different registry is required. This section
defines IANA registries for W3C Web Authentication (WebAuthn)
attestation statement format identifiers and extension identifiers
used in the context of a certificate request. This specification
establishes two registries:
* the "WebAuthn Attestation Statement Format Identifiers for
Certificate Request Protocols" registry
* the "WebAuthn Extension Identifiers for Certificate Request
Protocols" registry
Any additional processes established by the expert(s) after the
publication of this document will be recorded on the registry web
page at the discretion of the expert(s), who may differ from the
experts associated with the registry established by [RFC8809].
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NOTE: these two registries are shared with
[I-D.draft-bweeks-acme-device-attest], which features similar
registry establishment language. The registries need be created only
one time. Delete these sections if registry is already in place.
5.3.1. WebAuthn Attestation Statement Format Identifiers for
Certificate Request Protocols
WebAuthn attestation statement format identifiers are strings whose
semantic, syntactic, and string-matching criteria are specified in
the "Attestation Statement Format Identifiers"
(https://www.w3.org/TR/2019/REC-webauthn-1-20190304/#sctn-attstn-fmt-
ids) section of [WebAuthn], along with the concepts of attestation
and attestation statement formats.
Registered attestation statement format identifiers are those that
have been added to the registry by following the procedure in
Section 5.3.1.1.
Each attestation statement format identifier added to this registry
MUST be unique amongst the set of registered attestation statement
format identifiers.
Registered attestation statement format identifiers MUST be a maximum
of 32 octets in length and MUST consist only of printable ASCII
[RFC20] characters, excluding backslash and double quote, i.e., VCHAR
as defined in [RFC5234] but without %x22 and %x5c. Attestation
statement format identifiers are case sensitive and may not match
other registered identifiers in a case-insensitive manner unless the
designated experts determine that there is a compelling reason to
allow an exception.
5.3.1.1. Registering Attestation Statement Format Identifiers
WebAuthn attestation statement format identifiers are registered
using the Specification Required policy (see Section 4.6 of
[RFC8126]).
The "WebAuthn Attestation Statement Format Identifiers for
Certificate Request Protocols" registry is located at
https://www.iana.org/assignments/webauthn_for_certreq
(https://www.iana.org/assignments/webauthn_for_certreq).
Registration requests can be made by following the instructions
located there or by sending an email to the webauthn-for-certreq-reg-
review@ietf.org mailing list.
Registration requests consist of at least the following information:
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* WebAuthn Attestation Statement Format Identifier:
- An identifier meeting the requirements given in Section 5.3.1.
* Description:
- A relatively short description of the attestation format.
* Specification Document(s):
- Reference to the document or documents that specify the
attestation statement format.
* Change Controller:
- For Standards Track RFCs, list "IETF". For others, give the
name of the responsible party. Other details (e.g., postal
address, email address, home page URI) may also be included.
* Notes:
- [optional]
Registrations MUST reference a freely available, stable
specification, e.g., as described in Section 4.6 of [RFC8126]. This
specification MUST include security and privacy considerations
relevant to the attestation statement format.
Note that WebAuthn attestation statement format identifiers can be
registered by third parties (including the expert(s) themselves), if
the expert(s) determines that an unregistered attestation statement
format is widely deployed and not likely to be registered in a timely
manner otherwise. Such registrations still are subject to the
requirements defined, including the need to reference a
specification.
5.3.1.2. Registration Request Processing
As noted in Section 5.3.1.1, WebAuthn attestation statement format
identifiers are registered using the Specification Required policy.
The expert(s) will clearly identify any issues that cause a
registration to be refused, such as an incompletely specified
attestation format.
When a request is approved, the expert(s) will inform IANA, and the
registration will be processed. The IESG is the arbiter of any
objection.
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5.3.1.3. Initial Values in the WebAuthn Attestation Statement Format
Identifiers for Certificate Request Protocols Registry
The initial values for the "WebAuthn Attestation Statement Format
Identifiers for Certificate Request Protocols" registry have been
populated with the values listed in the "WebAuthn Attestation
Statement Format Identifier Registrations"
(https://www.w3.org/TR/2019/REC-webauthn-1-20190304/#sctn-att-fmt-
reg) section of [WebAuthn]. Also, the Change Controller entry for
each of those registrations is:
* Change Controller:
- W3C Web Authentication Working Group (public-webauthn@w3.org)
5.3.2. WebAuthn Extension Identifiers for Certificate Request Protocols
WebAuthn extension identifiers are strings whose semantic, syntactic,
and string-matching criteria are specified in the "Extension
Identifiers" (https://www.w3.org/TR/2019/REC-webauthn-1-
20190304/#sctn-extension-id) section of [WebAuthn].
Registered extension identifiers are those that have been added to
the registry by following the procedure in Section 5.3.2.1.
Each extension identifier added to this registry MUST be unique
amongst the set of registered extension identifiers.
Registered extension identifiers MUST be a maximum of 32 octets in
length and MUST consist only of printable ASCII characters, excluding
backslash and double quote, i.e., VCHAR as defined in [RFC5234] but
without %x22 and %x5c. Extension identifiers are case sensitive and
may not match other registered identifiers in a case-insensitive
manner unless the designated experts determine that there is a
compelling reason to allow an exception.
5.3.2.1. Registering Extension Identifiers
WebAuthn extension identifiers are registered using the Specification
Required policy (see Section 4.6 of [RFC8126]).
The "WebAuthn Extension Identifiers" registry is located at
https://www.iana.org/assignments/webauthn
(https://www.iana.org/assignments/webauthn). Registration requests
can be made by following the instructions located there or by sending
an email to the webauthn-for-certreq-reg-review@ietf.org mailing
list.
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Registration requests consist of at least the following information:
* WebAuthn Extension Identifier:
- An identifier meeting the requirements given in Section 5.3.2.
* Description:
- A relatively short description of the extension.
* Specification Document(s):
- Reference to the document or documents that specify the
extension.
* Change Controller:
- For Standards Track RFCs, list "IETF". For others, give the
name of the responsible party. Other details (e.g., postal
address, email address, home page URI) may also be included.
* Notes:
- [optional]
Registrations MUST reference a freely available, stable
specification, e.g., as described in Section 4.6 of [RFC8126]. This
specification MUST include security and privacy considerations
relevant to the extension.
Note that WebAuthn extensions can be registered by third parties
(including the expert(s) themselves), if the expert(s) determines
that an unregistered extension is widely deployed and not likely to
be registered in a timely manner otherwise. Such registrations still
are subject to the requirements defined, including the need to
reference a specification.
5.3.2.2. Registration Request Processing
As noted in Section 5.3.2.1, WebAuthn extension identifiers are
registered using the Specification Required policy.
The expert(s) will clearly identify any issues that cause a
registration to be refused, such as an incompletely specified
extension.
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When a request is approved, the expert(s) will inform IANA, and the
registration will be processed. The IESG is the arbiter of any
objection.
5.3.2.3. Initial Values in the WebAuthn Extension Identifiers Registry
The initial values for the "WebAuthn Extension Identifiers" registry
have been populated with the values listed in the "WebAuthn Extension
Identifier Registrations" https://www.w3.org/TR/2019/REC-webauthn-1-
20190304/#sctn-extensions-reg (https://www.w3.org/TR/2019/REC-
webauthn-1-20190304/#sctn-extensions-reg) section of [WebAuthn].
Also, the Change Controller entry for each of those registrations is:
* Change Controller:
- W3C Web Authentication Working Group (public-webauthn@w3.org)
6. ASN.1 Module
The following ASN.1 module makes use of the conventions from
[RFC5912].
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KeyAttestationExtn-2022
{ iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-keyAttestation(TBD2) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
IMPORTS
id-pe
FROM PKIX1Explicit-2009 -- from [RFC5912]
{ iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-explicit-02(51) }
EXTENSION, ATTRIBUTE
FROM PKIX-CommonTypes-2009 -- from [RFC5912]
{ iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) id-mod(0) id-mod-pkixCommon-02(57) }
;
-- EXPORT ALL --
ext-keyAttestation EXTENSION ::= {
SYNTAX KeyAttestation IDENTIFIED BY id-pe-keyAttestation }
attr-keyAttestation ATTRIBUTE ::= {
TYPE KeyAttestation IDENTIFIED BY id-pe-keyAttestation }
id-pe-keyAttestation OBJECT IDENTIFIER ::= { id-pe TBD }
KeyAttestation ::= OCTET STRING
END
7. References
7.1. Normative References
[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/rfc/rfc2119>.
[RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification
Request Syntax Specification Version 1.7", RFC 2986,
DOI 10.17487/RFC2986, November 2000,
<https://www.rfc-editor.org/rfc/rfc2986>.
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[RFC4210] Adams, C., Farrell, S., Kause, T., and T. Mononen,
"Internet X.509 Public Key Infrastructure Certificate
Management Protocol (CMP)", RFC 4210,
DOI 10.17487/RFC4210, September 2005,
<https://www.rfc-editor.org/rfc/rfc4210>.
[RFC4211] Schaad, J., "Internet X.509 Public Key Infrastructure
Certificate Request Message Format (CRMF)", RFC 4211,
DOI 10.17487/RFC4211, September 2005,
<https://www.rfc-editor.org/rfc/rfc4211>.
[RFC5272] Schaad, J. and M. Myers, "Certificate Management over CMS
(CMC)", RFC 5272, DOI 10.17487/RFC5272, June 2008,
<https://www.rfc-editor.org/rfc/rfc5272>.
[RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the
Public Key Infrastructure Using X.509 (PKIX)", RFC 5912,
DOI 10.17487/RFC5912, June 2010,
<https://www.rfc-editor.org/rfc/rfc5912>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<https://www.rfc-editor.org/rfc/rfc7030>.
[RFC7299] Housley, R., "Object Identifier Registry for the PKIX
Working Group", RFC 7299, DOI 10.17487/RFC7299, July 2014,
<https://www.rfc-editor.org/rfc/rfc7299>.
[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/rfc/rfc8174>.
[RFC8809] Hodges, J., Mandyam, G., and M. Jones, "Registries for Web
Authentication (WebAuthn)", RFC 8809,
DOI 10.17487/RFC8809, August 2020,
<https://www.rfc-editor.org/rfc/rfc8809>.
[RFC8894] Gutmann, P., "Simple Certificate Enrolment Protocol",
RFC 8894, DOI 10.17487/RFC8894, September 2020,
<https://www.rfc-editor.org/rfc/rfc8894>.
[WebAuthn] Hodges, J., Jones, J., Jones, M. B., Kumar, A., and E.
Lundberg, "Web Authentication: An API for accessing Public
Key Credentials Level 2", April 2021,
<https://www.w3.org/TR/webauthn-2/>.
7.2. Informative References
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[COTS] Wallace, C. and R. Housley, "Concise TA Stores (CoTS)",
June 2022.
[fido-metadata]
FIDO Alliance, "FIDO Metadata Statement", May 2021,
<https://fidoalliance.org/specs/mds/fido-metadata-
statement-v3.0-ps-20210518.html>.
[I-D.draft-bweeks-acme-device-attest]
Weeks, B., "Automated Certificate Management Environment
(ACME) Device Attestation Extension", Work in Progress,
Internet-Draft, draft-bweeks-acme-device-attest-01, 7
August 2022, <https://datatracker.ietf.org/doc/html/draft-
bweeks-acme-device-attest-01>.
[OTA] Apple, "Over-the-Air Profile Delivery and Configuration",
April 2018, <https://developer.apple.com/library/archive/d
ocumentation/NetworkingInternet/Conceptual/
iPhoneOTAConfiguration/Introduction/Introduction.html>.
[RFC8555] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
Kasten, "Automatic Certificate Management Environment
(ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019,
<https://www.rfc-editor.org/rfc/rfc8555>.
[WebAuthnReg]
IANA, "WebAuthn Attestation Statement Format Identifiers",
<https://www.iana.org/assignments/webauthn/
webauthn.xhtml>.
Acknowledgments
TODO acknowledge.
Authors' Addresses
Carl Wallace
Red Hound Software
Email: carl@redhoundsoftware.com
Sean Turner
sn3rd
Email: sean@sn3rd.com
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