JOSE Working Group M.B. Jones Internet-Draft independent Updates: 7518, 8037, 9053 (if approved) O. Steele Intended status: Standards Track Transmute Expires: 3 March 2024 31 August 2023 Fully-Specified Algorithms for JOSE and COSE draft-jones-jose-fully-specified-algorithms-01 Abstract This specification refers to cryptographic algorithm identifiers that fully specify the cryptographic operations to be performed, including any curve, key derivation function (KDF), hash functions, etc., as being "fully specified". Whereas, it refers to cryptographic algorithm identifiers that require additional information beyond the algorithm identifier to determine the cryptographic operations to be performed as being "polymorphic". This specification creates fully- specified algorithm identifiers for all registered JOSE and COSE polymorphic algorithm identifiers, enabling applications to use only fully-specified algorithm identifiers. 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 3 March 2024. Copyright Notice Copyright (c) 2023 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. Jones & Steele Expires 3 March 2024 [Page 1] Internet-Draft Fully-Specified Algorithms for JOSE and August 2023 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Notation and Conventions . . . . . . . . . . 3 2. Fully-specified Digital Signature Algorithm Identifiers . . . 4 2.1. Elliptic Curve Digital Signature Algorithm (ECDSA) . . . 4 2.2. Edwards-Curve Digital Signature Algorithm (EdDSA) . . . . 4 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 3.1. JOSE Algorithms Registrations . . . . . . . . . . . . . . 5 3.1.1. Fully-Specified JOSE Algorithm Registrations . . . . 5 3.1.2. Deprecated Polymorphic JOSE Algorithm Registrations . . . . . . . . . . . . . . . . . . . . 5 3.2. COSE Algorithms Registrations . . . . . . . . . . . . . . 6 3.2.1. Fully-Specified COSE Algorithm Registrations . . . . 6 3.2.2. Deprecated Polymorphic COSE Algorithm Registrations . . . . . . . . . . . . . . . . . . . . 7 3.3. Updated Review Instructions for Designated Experts . . . 7 4. Security Considerations . . . . . . . . . . . . . . . . . . . 8 5. To Do . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 6.1. Normative References . . . . . . . . . . . . . . . . . . 8 6.2. Informative References . . . . . . . . . . . . . . . . . 8 Appendix A. Document History . . . . . . . . . . . . . . . . . . 9 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 1. Introduction The IANA algorithm registries for JOSE [IANA.JOSE.Algorithms] and COSE [IANA.COSE.Algorithms] contain two kinds of algorithm identifiers: Fully Specified Those that fully determine the cryptographic operations to be performed, including any curve, key derivation function (KDF), hash functions, etc. Examples are RS256 and ES256K in both JOSE and COSE and ES256 in JOSE. Jones & Steele Expires 3 March 2024 [Page 2] Internet-Draft Fully-Specified Algorithms for JOSE and August 2023 Polymorphic Those requiring information beyond the algorithm identifier to determine the cryptographic operations to be performed. Such additional information could include the actual key value and a curve that it uses. Examples are EdDSA in both JOSE and COSE and ES256 in COSE. This matters because many protocols negotiate supported operations using only algorithm identifiers. For instance, OAuth Authorization Server Metadata [RFC8414] uses negotiation parameters like these (from an example in the specification): "token_endpoint_auth_signing_alg_values_supported": ["RS256", "ES256"] OpenID Connect Discovery [OpenID.Discovery] likewise negotiates supported algorithms using alg and enc values. W3C Web Authentication [WebAuthn] and FIDO Client to Authenticator Protocol (CTAP) [FIDO2] negotiate using COSE alg numbers. This does not work for polymorphic algorithms. For instance, with EdDSA, you do not know which of the curves Ed25519 and/or Ed448 are supported! This causes real problems in practice. WebAuthn contains this de-facto algorithm definition to work around this problem: -8 (EdDSA), where crv is 6 (Ed25519) This redefines the COSE EdDSA algorithm identifier for the purposes of WebAuthn to restrict it to using the Ed25519 curve - making it non-polymorphic so that algorithm negotiation can succeed, but also effectively eliminating the possibility of using Ed448. Other similar workarounds for polymorphic algorithm identifiers are used in practice. This specification creates fully-specified algorithm identifiers for all registered polymorphic JOSE and COSE algorithms and their parameters, enabling applications to use only fully-specified algorithm identifiers. It furthermore deprecates the practice of registering polymorphic algorithm identifiers. 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. Jones & Steele Expires 3 March 2024 [Page 3] Internet-Draft Fully-Specified Algorithms for JOSE and August 2023 2. Fully-specified Digital Signature Algorithm Identifiers This section creates fully-specified digital signature algorithm identifiers for all registered polymorphic JOSE and COSE algorithms and their parameters. 2.1. Elliptic Curve Digital Signature Algorithm (ECDSA) [RFC9053] defines the current use of the Elliptic Curve Digital Signature Algorithm (ECDSA) by COSE. The COSE algorithm registrations for ECDSA are polymorphic, since they do not specify the curve used. For instance, ES256 is defined as "ECDSA w/ SHA-256" in Section 2.1 of [RFC9053]. (The corresponding JOSE registrations in [RFC7518] are full-specified.) The following fully-specified COSE algorithms are defined: +========+=================+===================+==================+ | Name | COSE Value | Description | COSE Recommended | +========+=================+===================+==================+ | ESP256 | TBD (requested | ECDSA using P-256 | Yes | | | assignment -9) | curve and SHA-256 | | +--------+-----------------+-------------------+------------------+ | ESP384 | TBD (requested | ECDSA using P-384 | Yes | | | assignment -48) | curve and SHA-384 | | +--------+-----------------+-------------------+------------------+ | ESP512 | TBD (requested | ECDSA using P-521 | Yes | | | assignment -49) | curve and SHA-512 | | +--------+-----------------+-------------------+------------------+ Table 1: ECDSA Algorithm Values 2.2. Edwards-Curve Digital Signature Algorithm (EdDSA) [RFC8037] defines the current use of the Edwards-Curve Digital Signature Algorithm (EdDSA) by JOSE and [RFC9053] defines its current use by COSE. Both register polymorphic EdDSA algorithm identifiers. The following fully-specified JOSE and COSE algorithms are defined: Jones & Steele Expires 3 March 2024 [Page 4] Internet-Draft Fully-Specified Algorithms for JOSE and August 2023 +=======+============+=============+================+=============+ |Name | COSE Value | Description | JOSE | COSE | | | | | Implementation | Recommended | | | | | Requirements | | +=======+============+=============+================+=============+ |Ed25519| TBD | EdDSA using | Optional | No | | | (requested | Ed25519 | | | | | assignment | curve | | | | | -50) | | | | +-------+------------+-------------+----------------+-------------+ |Ed448 | TBD | EdDSA using | Optional | No | | | (requested | Ed448 curve | | | | | assignment | | | | | | -51) | | | | +-------+------------+-------------+----------------+-------------+ Table 2: EdDSA Algorithm Values 3. IANA Considerations 3.1. JOSE Algorithms Registrations This section registers the following values in the IANA "JSON Web Signature and Encryption Algorithms" registry [IANA.JOSE.Algorithms]. 3.1.1. Fully-Specified JOSE Algorithm Registrations * Algorithm Name: Ed25519 * Algorithm Description: EdDSA using Ed25519 curve * Algorithm Usage Locations: alg * JOSE Implementation Requirements: Optional * Change Controller: IESG * Reference: Section 2.2 of [[ this specification ]] * Algorithm Analysis Document(s): [RFC8032] * Algorithm Name: Ed448 * Algorithm Description: EdDSA using Ed448 curve * Algorithm Usage Locations: alg * JOSE Implementation Requirements: Optional * Change Controller: IESG * Reference: Section 2.2 of [[ this specification ]] * Algorithm Analysis Document(s): [RFC8032] 3.1.2. Deprecated Polymorphic JOSE Algorithm Registrations The following registration is updated to change its status to Deprecated. Jones & Steele Expires 3 March 2024 [Page 5] Internet-Draft Fully-Specified Algorithms for JOSE and August 2023 * Algorithm Name: EdDSA * Algorithm Description: EdDSA signature algorithms * Algorithm Usage Locations: alg * JOSE Implementation Requirements: Deprecated * Change Controller: IESG * Reference: Section 3.1 of RFC8037 * Algorithm Analysis Document(s): [RFC8032] 3.2. COSE Algorithms Registrations This section registers the following values in the IANA "COSE Algorithms" registry [IANA.COSE.Algorithms]. 3.2.1. Fully-Specified COSE Algorithm Registrations * Name: ESP256 * Value: TBD (requested assignment -9) * Description: ECDSA using P-256 curve and SHA-256 * Reference: Section 2.1 of this document * Recommended: Yes * Name: ESP384 * Value: TBD (requested assignment -48) * Description: ECDSA using P-384 curve and SHA-384 * Reference: Section 2.1 of this document * Recommended: Yes * Name: ESP512 * Value: TBD (requested assignment -49) * Description: ECDSA using P-521 curve and SHA-512 * Reference: Section 2.1 of this document * Recommended: Yes * Name: Ed25519 * Value: TBD (requested assignment -50) * Description: EdDSA using Ed25519 curve * Reference: Section 2.2 of this document * Recommended: Yes * Name: Ed448 * Value: TBD (requested assignment -51) * Description: EdDSA using Ed448 curve * Reference: Section 2.2 of this document * Recommended: Yes Jones & Steele Expires 3 March 2024 [Page 6] Internet-Draft Fully-Specified Algorithms for JOSE and August 2023 3.2.2. Deprecated Polymorphic COSE Algorithm Registrations The following registrations are updated to change their status to Deprecated. * Name: ES256 * Value: -7 * Description: ECDSA w/ SHA-256 * Reference: RFC 9053 * Recommended: Deprecated * Name: ES384 * Value: -35 * Description: ECDSA w/ SHA-384 * Reference: RFC 9053 * Recommended: Deprecated * Name: ES512 * Value: -36 * Description: ECDSA w/ SHA-512 * Reference: RFC 9053 * Recommended: Deprecated * Name: EdDSA * Value: -8 * Description: EdDSA * Reference: RFC 9053 * Recommended: Deprecated 3.3. Updated Review Instructions for Designated Experts The review instructions for the designated experts for the IANA "JSON Web Signature and Encryption Algorithms" registry [IANA.JOSE.Algorithms] in Section 7.1 of [RFC7518] are updated to add this additional review criterion: * Registration requests for polymorphic algorithm identifiers must not be accepted; only fully-specified algorithm identifiers may be registered going forward. The review instructions for the designated experts for the IANA "COSE Algorithms" registry [IANA.COSE.Algorithms] in Section 10.4 of [RFC9053] are also updated to add the same additional review criterion. Jones & Steele Expires 3 March 2024 [Page 7] Internet-Draft Fully-Specified Algorithms for JOSE and August 2023 4. Security Considerations Using fully-specified algorithm identifiers reduces the attack surface relative to using polymorphic algorithm identifiers, since it reduces the opportunity for attackers to choose algorithms. The security considerations for ECDSA in [RFC7518], for EdDSA in [RFC8037], and for ECDSA and EdDSA in [RFC9053] apply. 5. To Do Future versions of this specification may cover these additional topics: * State that key representations for the new fully-specified algorithms are the same as for the polymorphic algorithms that they replaced, other than the alg value, if included. * What other polymorphic algorithm registrations have we missed? * Discuss why varying RSA key sizes don't necessitate per-key-size algorithm identifiers. * Discuss the treatment of EDCH-ES and its ephemeral keys. 6. References 6.1. 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, . [RFC8037] Liusvaara, I., "CFRG Elliptic Curve Diffie-Hellman (ECDH) and Signatures in JSON Object Signing and Encryption (JOSE)", RFC 8037, DOI 10.17487/RFC8037, January 2017, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC9053] Schaad, J., "CBOR Object Signing and Encryption (COSE): Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053, August 2022, . 6.2. Informative References Jones & Steele Expires 3 March 2024 [Page 8] Internet-Draft Fully-Specified Algorithms for JOSE and August 2023 [FIDO2] Bradley, J., Hodges, J., Jones, M., Kumar, A., and J. Johan, "Client to Authenticator Protocol (CTAP)", FIDO Alliance Proposed Standard, 15 June 2021, . [IANA.COSE.Algorithms] IANA, "COSE Algorithms", . [IANA.JOSE.Algorithms] IANA, "JOSE Algorithms", . [OpenID.Discovery] Sakimura, N., Bradley, J., Jones, M.B., and E. Jay, "OpenID Connect Discovery 1.0", 8 November 2014, . [RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518, DOI 10.17487/RFC7518, May 2015, . [RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital Signature Algorithm (EdDSA)", RFC 8032, DOI 10.17487/RFC8032, January 2017, . [RFC8414] Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0 Authorization Server Metadata", RFC 8414, DOI 10.17487/RFC8414, June 2018, . [WebAuthn] Hodges, J., Jones, J.C., Jones, M., Kumar, A., and E. Lundberg, "Web Authentication: An API for accessing Public Key Credentials - Level 2", World Wide Web Consortium (W3C) Recommendation, 8 April 2021, . Appendix A. Document History [[ to be removed by the RFC Editor before publication as an RFC ]] -01 Jones & Steele Expires 3 March 2024 [Page 9] Internet-Draft Fully-Specified Algorithms for JOSE and August 2023 * Renamed ES25519 to Ed25519 and ES448 to Ed448, by popular demand! -00 * Initial version. Acknowledgements The authors thank John Bradley, Brian Campbell, Ilari Liusvarra, Tobias Looker, and Filip Skokan for their contributions to this specification. Authors' Addresses Michael B. Jones independent Email: michael_b_jones@hotmail.com URI: https://self-issued.info/ Orie Steele Transmute Email: orie@transmute.industries Jones & Steele Expires 3 March 2024 [Page 10]