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WebAuthn Working Group                                          M. Jones
Internet-Draft                                                 Microsoft
Intended status: Informational                              May 30, 2018
Expires: December 1, 2018


                   Using secp256k1 with JOSE and COSE
                   draft-jones-webauthn-secp256k1-00

Abstract

   This specification defines algorithm encodings and representations
   enabling the Standards for Efficient Cryptography Group (SECG)
   elliptic curve "secp256k1" to be used for JSON Object Signing and
   Encryption (JOSE) and CBOR Object Signing and Encryption (COSE)
   messages.

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
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   This Internet-Draft will expire on December 1, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Notation and Conventions . . . . . . . . . .   2
   2.  JOSE and COSE secp256k1 Curve Key Representations . . . . . .   2
   3.  ECDSA Signature with secp256k1 Curve  . . . . . . . . . . . .   3
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  JSON Web Key Elliptic Curve Registration  . . . . . . . .   3
     4.2.  JOSE Algorithm Registration . . . . . . . . . . . . . . .   3
     4.3.  COSE Elliptic Curves Registration . . . . . . . . . . . .   4
     4.4.  COSE Algorithm Registration . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   6
   Document History  . . . . . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   This specification 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.  The elliptic curve and
   associated algorithm are registered in appropriate IANA JOSE and COSE
   registries.

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.  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": "P-256K"

   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): "P-256K" (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.  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:

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

                      Table 1: ECDSA Algorithm Values

4.  IANA Considerations

4.1.  JSON Web Key Elliptic Curve Registration

   This section registers the following value in the IANA "JSON Web Key
   Elliptic Curve" registry [IANA.JOSE.Curves].

   o  Curve Name: P-256K
   o  Curve Description: SECG secp256k1 Curve
   o  JOSE Implementation Requirements: Optional
   o  Change Controller: IESG
   o  Specification Document(s): Section 2 of [[ this specification ]]

4.2.  JOSE Algorithm Registration

   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 w/ secp256k1 Curve
   o  Algorithm Usage Locations: alg



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   o  JOSE Implementation Requirements: Optional
   o  Change Controller: IESG
   o  Reference: Section 3 of [[ this specification ]]
   o  Algorithm Analysis Document(s): [SEC2]

4.3.  COSE Elliptic Curves Registration

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

   o  Name: P-256K
   o  Value: TBD (requested assignment 8)
   o  Key Type: EC2
   o  Description: SECG secp256k1 Curve
   o  Change Controller: IESG
   o  Reference: Section 2 of [[ this specification ]]
   o  Recommended: Yes

4.4.  COSE Algorithm Registration

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

   o  Name: ES256K
   o  Value: TBD (requested assignment -43)
   o  Description: ECDSA w/ secp256k1 Curve
   o  Reference: Section 3 of this document
   o  Recommended: Yes

5.  Security Considerations

   Care should be taken that a secp256k1 key not be 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>.




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   [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>.

   [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>.

   [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>.

   [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

   [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>.





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   [IANA.JOSE.Curves]
              IANA, "JSON Web Key Elliptic Curve",
              <https://www.iana.org/assignments/jose/
              jose.xhtml#web-key-elliptic-curve>.

Acknowledgements

   TBD

Document History

   [[ to be removed by the RFC Editor before publication as an RFC ]]

   -00

   o  Initial version.

Author's Address

   Michael B. Jones
   Microsoft

   Email: mbj@microsoft.com
   URI:   http://self-issued.info/



























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