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Versions: (draft-jones-cose-additional-algorithms)
00 01 02 03
COSE Working Group M. Jones
Internet-Draft Microsoft
Intended status: Standards Track July 8, 2019
Expires: January 9, 2020
COSE and JOSE Registrations for WebAuthn Algorithms
draft-ietf-cose-webauthn-algorithms-01
Abstract
The W3C Web Authentication (WebAuthn) specification and the FIDO2
Client to Authenticator Protocol (CTAP) specification use COSE
algorithm identifiers. This specification registers algorithms in
the IANA "COSE Algorithms" registry that are used by WebAuthn and
CTAP implementations that are not already registered. Also, they are
registered in the IANA "JSON Web Signature and Encryption Algorithms"
registry, when not already registered there.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 9, 2020.
Copyright Notice
Copyright (c) 2019 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 extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Notation and Conventions . . . . . . . . . . 2
2. RSASSA-PKCS1-v1_5 Signature Algorithm . . . . . . . . . . . . 3
3. Using secp256k1 with JOSE and COSE . . . . . . . . . . . . . 3
3.1. JOSE and COSE secp256k1 Curve Key Representations . . . . 3
3.2. ECDSA Signature with secp256k1 Curve . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
4.1. COSE Algorithms Registrations . . . . . . . . . . . . . . 5
4.2. COSE Elliptic Curves Registrations . . . . . . . . . . . 6
4.3. JOSE Algorithms Registrations . . . . . . . . . . . . . . 6
4.4. JSON Web Key Elliptic Curves Registrations . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5.1. RSA Key Size Security Considerations . . . . . . . . . . 6
5.2. RSASSA-PKCS1-v1_5 with SHA-2 Security Considerations . . 7
5.3. RSASSA-PKCS1-v1_5 with SHA-1 Security Considerations . . 7
5.4. secp256k1 Security Considerations . . . . . . . . . . . . 7
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Normative References . . . . . . . . . . . . . . . . . . 7
6.2. Informative References . . . . . . . . . . . . . . . . . 8
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 9
Document History . . . . . . . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
This specification defines how to use several algorithms with COSE
[RFC8152] that are used by implementations of the W3C Web
Authentication (WebAuthn) [WebAuthn] and FIDO2 Client to
Authenticator Protocol (CTAP) [CTAP] specifications. These
algorithms are registered in the IANA "COSE Algorithms" registry
[IANA.COSE.Algorithms] and also in the IANA "JSON Web Signature and
Encryption Algorithms" registry [IANA.JOSE.Algorithms], when not
already registered there.
1.1. Requirements Notation and Conventions
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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2. RSASSA-PKCS1-v1_5 Signature Algorithm
The RSASSA-PKCS1-v1_5 signature algorithm is defined in [RFC8017].
The RSASSA-PKCS1-v1_5 signature algorithm is parameterized with a
hash function (h).
A key of size 2048 bits or larger MUST be used with these algorithms.
Implementations need to check that the key type is 'RSA' when
creating or verifying a signature.
The RSASSA-PKCS1-v1_5 algorithms specified in this document are in
the following table.
+-------+-----------------------------+---------+-------------------+
| Name | Value | Hash | Description |
+-------+-----------------------------+---------+-------------------+
| RS256 | TBD (temporary assignment | SHA-256 | RSASSA-PKCS1-v1_5 |
| | -257 already in place) | | using SHA-256 |
| RS384 | TBD (temporary assignment | SHA-384 | RSASSA-PKCS1-v1_5 |
| | -258 already in place) | | using SHA-384 |
| RS512 | TBD (temporary assignment | SHA-512 | RSASSA-PKCS1-v1_5 |
| | -259 already in place) | | using SHA-512 |
| RS1 | TBD (temporary assignment | SHA-1 | RSASSA-PKCS1-v1_5 |
| | -65535 already in place) | | using SHA-1 |
+-------+-----------------------------+---------+-------------------+
Table 1: RSASSA-PKCS1-v1_5 Algorithm Values
3. Using secp256k1 with JOSE and COSE
This section defines algorithm encodings and representations enabling
the Standards for Efficient Cryptography Group (SECG) elliptic curve
secp256k1 [SEC2] to be used for JSON Object Signing and Encryption
(JOSE) [RFC7515] and CBOR Object Signing and Encryption (COSE)
[RFC8152] messages.
3.1. JOSE and COSE secp256k1 Curve Key Representations
The Standards for Efficient Cryptography Group (SECG) elliptic curve
secp256k1 [SEC2] is represented in a JSON Web Key (JWK) [RFC7517]
using these values:
o "kty": "EC"
o "crv": "secp256k1"
plus "x" and "y" values to represent the curve point for the key.
Other optional values such as "alg" MAY also be present.
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It is represented in a COSE_Key [RFC8152] using these values:
o "kty" (1): "EC2" (2)
o "crv" (-1): "secp256k1" (TBD - requested assignment 8)
plus "x" (-2) and "y" (-3) values to represent the curve point for
the key. Other optional values such as "alg" (3) MAY also be
present.
3.2. ECDSA Signature with secp256k1 Curve
The ECDSA signature algorithm is defined in [DSS]. This
specification defines the use of ECDSA with the secp256k1 curve and
the SHA-256 [DSS] cryptographic hash function. Implementations need
to check that the key type is "EC" for JOSE or "EC2" (2) for COSE
when creating or verifying a signature.
The ECDSA secp256k1 SHA-256 digital signature is generated as
follows:
1. Generate a digital signature of the JWS Signing Input or the COSE
payload using ECDSA secp256k1 SHA-256 with the desired private
key. The output will be the pair (R, S), where R and S are
256-bit unsigned integers.
2. Turn R and S into octet sequences in big-endian order, with each
array being be 32 octets long. The octet sequence
representations MUST NOT be shortened to omit any leading zero
octets contained in the values.
3. Concatenate the two octet sequences in the order R and then S.
(Note that many ECDSA implementations will directly produce this
concatenation as their output.)
4. The resulting 64-octet sequence is the JWS Signature or COSE
signature value.
The ECDSA secp256k1 SHA-256 algorithm specified in this document uses
these identifiers:
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+------------+------------------------+-----------------------------+
| JOSE Alg | COSE Alg Value | Description |
| Name | | |
+------------+------------------------+-----------------------------+
| ES256K | TBD (requested | ECDSA using secp256k1 curve |
| | assignment -43) | and SHA-256 |
+------------+------------------------+-----------------------------+
Table 2: ECDSA Algorithm Values
4. IANA Considerations
4.1. COSE Algorithms Registrations
This section registers the following values in the IANA "COSE
Algorithms" registry [IANA.COSE.Algorithms].
o Name: RS256
o Value: TBD (temporary assignment -257 already in place)
o Description: RSASSA-PKCS1-v1_5 using SHA-256
o Reference: Section 2 of this document
o Recommended: No
o Name: RS384
o Value: TBD (temporary assignment -258 already in place)
o Description: RSASSA-PKCS1-v1_5 using SHA-384
o Reference: Section 2 of this document
o Recommended: No
o Name: RS512
o Value: TBD (temporary assignment -259 already in place)
o Description: RSASSA-PKCS1-v1_5 using SHA-512
o Reference: Section 2 of this document
o Recommended: No
o Name: RS1
o Value: TBD (temporary assignment -65535 already in place)
o Description: RSASSA-PKCS1-v1_5 using SHA-1
o Reference: Section 2 of this document
o Recommended: Deprecated
o Name: ES256K
o Value: TBD (requested assignment -43)
o Description: ECDSA using secp256k1 curve and SHA-256
o Reference: Section 3.2 of this document
o Recommended: Yes
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4.2. COSE Elliptic Curves Registrations
This section registers the following value in the IANA "COSE Elliptic
Curves" registry [IANA.COSE.Curves].
o Name: secp256k1
o Value: TBD (requested assignment 8)
o Key Type: EC2
o Description: SECG secp256k1 curve
o Change Controller: IESG
o Reference: Section 3.1 of [[ this specification ]]
o Recommended: Yes
4.3. JOSE Algorithms Registrations
This section registers the following value in the IANA "JSON Web
Signature and Encryption Algorithms" registry [IANA.JOSE.Algorithms].
o Algorithm Name: ES256K
o Algorithm Description: ECDSA using secp256k1 curve and SHA-256
o Algorithm Usage Locations: alg
o JOSE Implementation Requirements: Optional
o Change Controller: IESG
o Reference: Section 3.2 of [[ this specification ]]
o Algorithm Analysis Document(s): [SEC2]
4.4. JSON Web Key Elliptic Curves Registrations
This section registers the following value in the IANA "JSON Web Key
Elliptic Curve" registry [IANA.JOSE.Curves].
o Curve Name: secp256k1
o Curve Description: SECG secp256k1 curve
o JOSE Implementation Requirements: Optional
o Change Controller: IESG
o Specification Document(s): Section 3.1 of [[ this specification ]]
5. Security Considerations
5.1. RSA Key Size Security Considerations
The security considerations on key sizes for RSA algorithms from
Section 6.1 of [RFC8230] also apply to the RSA algorithms in this
specification.
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5.2. RSASSA-PKCS1-v1_5 with SHA-2 Security Considerations
The security considerations on the use of RSASSA-PKCS1-v1_5 with
SHA-2 hash functions from Section 8.3 of [RFC7518] also apply to
their use in this specification. For that reason, these algorithms
are registered as being "Not Recommended".
5.3. RSASSA-PKCS1-v1_5 with SHA-1 Security Considerations
The security considerations on the use of the SHA-1 hash function
from [RFC6194] apply in this specification. For that reason, the
"RS1" algorithm is registered as "Deprecated". It MUST NOT be used
by COSE implementations.
A COSE algorithm identifier for this algorithm is nonetheless being
registered because deployed TPMs continue to use it, and therefore
WebAuthn implementations need a COSE algorithm identifier for "RS1"
when TPM attestations using this algorithm are being represented.
5.4. secp256k1 Security Considerations
Care should be taken that a secp256k1 key is not mistaken for a P-256
key, given that their representations are the same except for the
"crv" value.
The procedures and security considerations described in the [SEC1],
[SEC2], and [DSS] specifications apply to implementations of this
specification.
6. References
6.1. Normative References
[DSS] National Institute of Standards and Technology (NIST),
"Digital Signature Standard (DSS)", FIPS PUB 186-4, July
2013, <http://nvlpubs.nist.gov/nistpubs/FIPS/
NIST.FIPS.186-4.pdf>.
[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>.
[RFC6194] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security
Considerations for the SHA-0 and SHA-1 Message-Digest
Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011,
<https://www.rfc-editor.org/info/rfc6194>.
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[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <https://www.rfc-editor.org/info/rfc7049>.
[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>.
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517,
DOI 10.17487/RFC7517, May 2015,
<https://www.rfc-editor.org/info/rfc7517>.
[RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
DOI 10.17487/RFC7518, May 2015,
<https://www.rfc-editor.org/info/rfc7518>.
[RFC8017] Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch,
"PKCS #1: RSA Cryptography Specifications Version 2.2",
RFC 8017, DOI 10.17487/RFC8017, November 2016,
<https://www.rfc-editor.org/info/rfc8017>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.
[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>.
[RFC8230] Jones, M., "Using RSA Algorithms with CBOR Object Signing
and Encryption (COSE) Messages", RFC 8230,
DOI 10.17487/RFC8230, September 2017,
<https://www.rfc-editor.org/info/rfc8230>.
[SEC1] Standards for Efficient Cryptography Group, "SEC 1:
Elliptic Curve Cryptography", Version 2.0, May 2009,
<http://www.secg.org/sec1-v2.pdf>.
[SEC2] Standards for Efficient Cryptography Group, "SEC 2:
Recommended Elliptic Curve Domain Parameters",
Version 2.0, January 2010,
<http://www.secg.org/sec2-v2.pdf>.
6.2. Informative References
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[CTAP] Brand, C., Czeskis, A., Ehrensvaerd, J., Jones, M., Kumar,
A., Lindemann, R., Powers, A., and J. Verrept, "Client to
Authenticator Protocol (CTAP)", FIDO Alliance Proposed
Standard, January 2019, <https://fidoalliance.org/specs/
fido-v2.0-ps-20190130/fido-client-to-authenticator-
protocol-v2.0-ps-20190130.html>.
[IANA.COSE.Algorithms]
IANA, "COSE Algorithms",
<https://www.iana.org/assignments/cose/
cose.xhtml#algorithms>.
[IANA.COSE.Curves]
IANA, "COSE Elliptic Curves",
<https://www.iana.org/assignments/cose/
cose.xhtml#elliptic-curves>.
[IANA.JOSE.Algorithms]
IANA, "JSON Web Signature and Encryption Algorithms",
<https://www.iana.org/assignments/jose/
jose.xhtml#web-signature-encryption-algorithms>.
[IANA.JOSE.Curves]
IANA, "JSON Web Key Elliptic Curve",
<https://www.iana.org/assignments/jose/
jose.xhtml#web-key-elliptic-curve>.
[WebAuthn]
Balfanz, D., Czeskis, A., Hodges, J., Jones, J., Jones,
M., Kumar, A., Liao, A., Lindemann, R., and E. Lundberg,
"Web Authentication: An API for accessing Public Key
Credentials - Level 1", World Wide Web Consortium
(W3C) Recommendation, March 2019,
<https://www.w3.org/TR/2019/REC-webauthn-1-20190304/>.
Acknowledgements
Thanks to Stephen Farrell, John Fontana, Jeff Hodges, John Mattsson,
Tony Nadalin, Matt Palmer, Jim Schaad, Goeran Selander, Wendy
Seltzer, Sean Turner, and Samuel Weiler for their roles in
registering these algorithm identifiers.
Document History
[[ to be removed by the RFC Editor before publication as an RFC ]]
-01
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o Changed the JOSE curve identifier from "P-256K" to "secp256k1".
o Specified that secp256k1 signing is done using the SHA-256 hash
function.
-00
o Created the initial working group draft from draft-jones-cose-
additional-algorithms-00, changing only the title, date, and
history entry.
Author's Address
Michael B. Jones
Microsoft
Email: mbj@microsoft.com
URI: http://self-issued.info/
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