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.

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Table of Contents

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

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:

• kty: EC
• 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.

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

• kty (1): EC2 (2)
• 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:

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].

• Curve Name: P-256K
• Curve Description: SECG secp256k1 Curve
• JOSE Implementation Requirements: Optional
• Change Controller: IESG
• 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].

• Algorithm Name: ES256K
• Algorithm Description: ECDSA w/ secp256k1 Curve
• Algorithm Usage Locations: alg
• JOSE Implementation Requirements: Optional
• Change Controller: IESG
• Reference: Section 3 of [[ this specification ]]
• 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].

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

4.4. COSE Algorithm Registration

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

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

6.2. Informative References

Acknowledgements

TBD

Document History

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

-00

• Initial version.

Author's Address