COSE Working Group M. Jones
Internet-Draft Microsoft
Intended status: Standards Track March 11, 2019
Expires: September 12, 2019

Additional Algorithm Registrations for COSE and JOSE
draft-jones-cose-additional-algorithms-00

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

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Table of Contents

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.

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.

RSASSA-PKCS1-v1_5 Algorithm Values
Name Value Hash Description
RS256 TBD (temporary assignment -257 already in place) SHA-256 RSASSA-PKCS1-v1_5 w/ SHA-256
RS384 TBD (temporary assignment -258 already in place) SHA-384 RSASSA-PKCS1-v1_5 w/ SHA-384
RS512 TBD (temporary assignment -259 already in place) SHA-512 RSASSA-PKCS1-v1_5 w/ SHA-512
RS1 TBD (temporary assignment -65535 already in place) SHA-1 RSASSA-PKCS1-v1_5 w/ SHA-1

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:

plus x and y values to represent the curve point for the key. Other optional values such as alg MAY also be present.

It is represented in a COSE_Key [RFC8152] using these values:

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]. 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 algorithm specified in this document is:

ECDSA Algorithm Values
JOSE Alg Name COSE Alg Value Description
ES256K TBD (requested assignment -43) ECDSA w/ secp256k1 Curve

4. IANA Considerations

4.1. COSE Algorithms Registrations

This section registers the following values in the IANA "COSE Algorithms" registry [IANA.COSE.Algorithms].

4.2. COSE Elliptic Curves Registrations

This section registers the following value in the IANA "COSE Elliptic Curves" registry [IANA.COSE.Curves].

4.3. JOSE Algorithms Registrations

This section registers the following value in the IANA "JSON Web Signature and Encryption Algorithms" registry [IANA.JOSE.Algorithms].

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].

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.

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.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[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.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, October 2013.
[RFC7515] Jones, M., Bradley, J. and N. Sakimura, "JSON Web Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May 2015.
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517, DOI 10.17487/RFC7517, May 2015.
[RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518, DOI 10.17487/RFC7518, May 2015.
[RFC8017] Moriarty, K., Kaliski, B., Jonsson, J. and A. Rusch, "PKCS #1: RSA Cryptography Specifications Version 2.2", RFC 8017, DOI 10.17487/RFC8017, November 2016.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)", RFC 8152, DOI 10.17487/RFC8152, July 2017.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[RFC8230] Jones, M., "Using RSA Algorithms with CBOR Object Signing and Encryption (COSE) Messages", RFC 8230, DOI 10.17487/RFC8230, September 2017.
[SEC1] Standards for Efficient Cryptography Group, "SEC 1: Elliptic Curve Cryptography", Version 2.0, May 2009.
[SEC2] Standards for Efficient Cryptography Group, "SEC 2: Recommended Elliptic Curve Domain Parameters", Version 2.0, January 2010.

6.2. Informative References

[CTAP] Brand, C., Czeskis, A., Ehrensvärd, J., Jones, M., Kumar, A., Lindemann, R., Powers, A. and J. Verrept, "Client to Authenticator Protocol (CTAP)", FIDO Alliance Proposed Standard, January 2019.
[IANA.COSE.Algorithms] IANA, "COSE Algorithms"
[IANA.COSE.Curves] IANA, "COSE Elliptic Curves"
[IANA.JOSE.Algorithms] IANA, "JSON Web Signature and Encryption Algorithms"
[IANA.JOSE.Curves] IANA, "JSON 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.

Acknowledgements

Thanks to John Fontana, Jeff Hodges, Tony Nadalin, Jim Schaad, Göran 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 ]]

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Author's Address

Michael B. Jones Microsoft EMail: mbj@microsoft.com URI: http://self-issued.info/