



Internet Engineering Task Force (IETF)                        M.B. Jones
Request for Comments: 9864                        Self-Issued Consulting
Updates: 7518, 8037, 9053                                      O. Steele
Category: Standards Track                                   Tradeverifyd
ISSN: 2070-1721                                             October 2025


Fully-Specified Algorithms for JSON Object Signing and Encryption (JOSE)
             and CBOR Object Signing and Encryption (COSE)

Abstract

   This specification refers to cryptographic algorithm identifiers that
   fully specify the cryptographic operations to be performed, including
   any curve, key derivation function (KDF), and hash functions, as
   being "fully specified".  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 registered JSON Object Signing and
   Encryption (JOSE) and CBOR Object Signing and Encryption (COSE)
   polymorphic algorithm identifiers, enabling applications to use only
   fully-specified algorithm identifiers.  It deprecates those
   polymorphic algorithm identifiers.

   This specification updates RFCs 7518, 8037, and 9053.  It deprecates
   polymorphic algorithms defined by RFCs 8037 and 9053 and provides
   fully-specified replacements for them.  It adds to the instructions
   to designated experts in RFCs 7518 and 9053.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9864.

Copyright Notice

   Copyright (c) 2025 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 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
     1.1.  Requirements Notation and Conventions
   2.  Fully-Specified Digital Signature Algorithm Identifiers
     2.1.  Elliptic Curve Digital Signature Algorithm (ECDSA)
     2.2.  Edwards-curve Digital Signature Algorithm (EdDSA)
   3.  Fully-Specified Encryption
     3.1.  Fully-Specified Encryption Algorithms
     3.2.  Polymorphic Encryption Algorithms
   4.  IANA Considerations
     4.1.  JOSE Algorithm Registrations
       4.1.1.  Fully-Specified JOSE Algorithm Registrations
       4.1.2.  Deprecated Polymorphic JOSE Algorithm Registration
     4.2.  COSE Algorithm Registrations
       4.2.1.  Fully-Specified COSE Algorithm Registrations
       4.2.2.  Deprecated Polymorphic COSE Algorithm Registrations
     4.3.  Updated Review Instructions for Designated Experts
       4.3.1.  JSON Web Signature and Encryption Algorithms
       4.3.2.  COSE Algorithms
     4.4.  Defining "Deprecated" and "Prohibited"
   5.  Key Representations
   6.  Notes on Algorithms Not Updated
     6.1.  RSA Signing Algorithms
     6.2.  ECDH Key Agreement Algorithms
     6.3.  HSS/LMS Hash-Based Digital Signature Algorithm
   7.  Security Considerations
   8.  References
     8.1.  Normative References
     8.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   The IANA algorithm registries for JSON Object Signing and Encryption
   (JOSE) algorithms [IANA.JOSE] and CBOR Object Signing and Encryption
   (COSE) algorithms [IANA.COSE] 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), and
      hash functions.  Examples are RS256 and ES256K in both JOSE
      [IANA.JOSE] and COSE [IANA.COSE] and ES256 in JOSE.

   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 the Edwards-curve Digital
      Signature Algorithm (EdDSA) in both JOSE [IANA.JOSE] and COSE
      [IANA.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 that 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 the FIDO Client to Authenticator
   Protocol (CTAP) [FIDO2] negotiate using COSE "alg" numbers.

   This does not work for polymorphic algorithms.  For instance, with
   EdDSA, it is not known 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.

   Note that using fully-specified algorithms is sometimes referred to
   as the "cipher suite" approach; using polymorphic algorithms is
   sometimes referred to as the "à la carte" approach.

   This specification creates fully-specified algorithm identifiers for
   registered polymorphic JOSE and COSE algorithms and their parameters,
   enabling applications to use only fully-specified algorithm
   identifiers.  Furthermore, it 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.

2.  Fully-Specified Digital Signature Algorithm Identifiers

   This section creates fully-specified digital signature algorithm
   identifiers for a set of registered polymorphic JOSE and COSE
   algorithms and their parameters.

2.1.  Elliptic Curve Digital Signature Algorithm (ECDSA)

   [RFC9053] defines a way to use the Elliptic Curve Digital Signature
   Algorithm (ECDSA) with 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
   fully specified.)

   The following fully-specified COSE ECDSA algorithms are defined by
   this specification:

    +========+============+=============================+=============+
    | Name   | COSE Value | Description                 | COSE        |
    |        |            |                             | Recommended |
    +========+============+=============================+=============+
    | ESP256 | -9         | ECDSA using P-256 curve and | Yes         |
    |        |            | SHA-256                     |             |
    +--------+------------+-----------------------------+-------------+
    | ESP384 | -51        | ECDSA using P-384 curve and | Yes         |
    |        |            | SHA-384                     |             |
    +--------+------------+-----------------------------+-------------+
    | ESP512 | -52        | ECDSA using P-521 curve and | Yes         |
    |        |            | SHA-512                     |             |
    +--------+------------+-----------------------------+-------------+
    | ESB256 | -265       | ECDSA using BrainpoolP256r1 | No          |
    |        |            | curve and SHA-256           |             |
    +--------+------------+-----------------------------+-------------+
    | ESB320 | -266       | ECDSA using BrainpoolP320r1 | No          |
    |        |            | curve and SHA-384           |             |
    +--------+------------+-----------------------------+-------------+
    | ESB384 | -267       | ECDSA using BrainpoolP384r1 | No          |
    |        |            | curve and SHA-384           |             |
    +--------+------------+-----------------------------+-------------+
    | ESB512 | -268       | ECDSA using BrainpoolP512r1 | No          |
    |        |            | curve and SHA-512           |             |
    +--------+------------+-----------------------------+-------------+

                      Table 1: ECDSA Algorithm Values

2.2.  Edwards-curve Digital Signature Algorithm (EdDSA)

   [RFC8037] defines a way to use EdDSA with JOSE, and [RFC9053] defines
   a way to use it with COSE.  Both register polymorphic EdDSA algorithm
   identifiers.

   The following fully-specified JOSE and COSE EdDSA algorithms are
   defined by this specification:

    +=========+=======+================+================+=============+
    | Name    | COSE  | Description    | JOSE           | COSE        |
    |         | Value |                | Implementation | Recommended |
    |         |       |                | Requirements   |             |
    +=========+=======+================+================+=============+
    | Ed25519 | -19   | EdDSA using    | Optional       | Yes         |
    |         |       | the Ed25519    |                |             |
    |         |       | parameter set  |                |             |
    |         |       | in Section 5.1 |                |             |
    |         |       | of [RFC8032]   |                |             |
    +---------+-------+----------------+----------------+-------------+
    | Ed448   | -53   | EdDSA using    | Optional       | Yes         |
    |         |       | the Ed448      |                |             |
    |         |       | parameter set  |                |             |
    |         |       | in Section 5.2 |                |             |
    |         |       | of [RFC8032]   |                |             |
    +---------+-------+----------------+----------------+-------------+

                      Table 2: EdDSA Algorithm Values

3.  Fully-Specified Encryption

   This section describes the construction of fully-specified encryption
   algorithm identifiers in the context of the JOSE and COSE encryption
   schemes JSON Web Encryption (JWE), as described in [RFC7516] and
   [RFC7518], and COSE encryption, as described in [RFC9052] and
   [RFC9053].

   Using fully-specified encryption algorithms enables the sender and
   receiver to agree on all mandatory security parameters.  They also
   enable protocols to specify an allow list of algorithm combinations
   that does not include polymorphic combinations, preventing problems
   such as cross-curve key establishment, cross-protocol symmetric
   encryption, or mismatched KDF size to symmetric key scenarios.

   Both JOSE and COSE have operations that take multiple algorithms as
   parameters.  Encrypted objects in JOSE [RFC7516] use two algorithm
   identifiers: the first in the "alg" (Algorithm) Header Parameter,
   which specifies how to determine the content encryption key, and the
   second in the "enc" (Encryption Algorithm) Header Parameter, which
   specifies the content encryption algorithm.  Likewise, encrypted COSE
   objects can use multiple algorithms for corresponding purposes.  This
   section describes how to fully specify encryption algorithms for JOSE
   and COSE.

   To perform fully-specified encryption in JOSE, the "alg" value MUST
   specify all parameters for key establishment or derive some of them
   from the accompanying "enc" value, and the "enc" value MUST specify
   all parameters for symmetric encryption.  For example, encryption via
   JWE using an "alg" value of "A128KW" (AES Key Wrap using 128-bit key)
   and an "enc" value of "A128GCM" (AES GCM using 128-bit key) uses
   fully-specified algorithms.

   Note that in JOSE, there is the option to derive some cryptographic
   parameters used in the "alg" computation from the accompanying "enc"
   value.  For example, the keydatalen KDF parameter value for "ECDH-ES"
   is determined from the "enc" value, as described in Section 4.6.2 of
   [RFC7518].  For the purposes of an "alg" value being fully specified,
   deriving parameters from "enc" does not make the algorithm
   polymorphic, as the computation is still fully determined by the
   algorithm identifiers used.  This option is not present in COSE.

   To perform fully-specified encryption in COSE, the outer "alg" value
   MUST specify all parameters for key establishment, and the inner
   "alg" value MUST specify all parameters for symmetric encryption.
   For example, encryption via COSE using an outer "alg" value of
   "A128KW" and an inner "alg" value of "A128GCM" uses fully-specified
   algorithms.  Note that when using COSE_Encrypt, as specified in
   Section 5.1 of [RFC9052], the outer "alg" is communicated in the
   headers of the COSE_Encrypt object and the inner "alg" is
   communicated in the headers of the COSE_recipient object.

   While this specification provides a definition of what fully-
   specified encryption algorithm identifiers are for both JOSE and
   COSE, it does not deprecate any polymorphic encryption algorithms,
   since replacements for them are not provided by this specification.
   This is discussed in Section 6.2.

3.1.  Fully-Specified Encryption Algorithms

   Many of the registered JOSE and COSE algorithms used for encryption
   are already fully specified.  This section discusses them.

   All the symmetric encryption algorithms registered by [RFC7518] and
   [RFC9053] are fully specified.  An example of a fully-specified
   symmetric encryption algorithm is "A128GCM" (AES GCM using 128-bit
   key).

   In both JOSE and COSE, all registered key wrapping algorithms are
   fully specified, as are the algorithms performing key wrapping using
   AES GCM.  An example of a fully-specified key wrapping algorithm is
   "A128KW" (AES Key Wrap using 128-bit key).

   The JOSE "dir" and COSE "direct" algorithms are fully specified.  The
   COSE direct+HKDF algorithms are fully specified.

   The JOSE algorithms performing Key Encryption with PBES2 are fully
   specified.

3.2.  Polymorphic Encryption Algorithms

   Some of the registered JOSE and COSE algorithms used for encryption
   are polymorphic.  This section discusses them.

   The Elliptic Curve Diffie-Hellman (ECDH) key establishment algorithms
   in both JOSE and COSE are polymorphic because they do not specify the
   elliptic curve to be used for the key.  This is true of the ephemeral
   key for the Ephemeral-Static (ES) algorithms registered for JOSE and
   COSE and of the static key for the Static-Static (SS) algorithms
   registered by COSE.  See more discussion of ECDH algorithms in
   Section 6.2.

4.  IANA Considerations

4.1.  JOSE Algorithm Registrations

   IANA has registered the values in this section in the "JSON Web
   Signature and Encryption Algorithms" registry [IANA.JOSE] established
   by [RFC7518] and has listed this document as an additional reference
   for the registry.

4.1.1.  Fully-Specified JOSE Algorithm Registrations

   Algorithm Name:  Ed25519
   Algorithm Description:  EdDSA using the Ed25519 parameter set in
      Section 5.1 of [RFC8032]
   Algorithm Usage Locations:  alg
   JOSE Implementation Requirements:  Optional
   Change Controller:  IETF
   Reference:  Section 2.2 of RFC 9864
   Algorithm Analysis Document(s):  [RFC8032]

   Algorithm Name:  Ed448
   Algorithm Description:  EdDSA using the Ed448 parameter set in
      Section 5.2 of [RFC8032]
   Algorithm Usage Locations:  alg
   JOSE Implementation Requirements:  Optional
   Change Controller:  IETF
   Reference:  Section 2.2 of RFC 9864
   Algorithm Analysis Document(s):  [RFC8032]

4.1.2.  Deprecated Polymorphic JOSE Algorithm Registration

   IANA has updated the status to "Deprecated" for the following
   registration.

   Algorithm Name:  EdDSA
   Algorithm Description:  EdDSA signature algorithms
   Algorithm Usage Locations:  alg
   JOSE Implementation Requirements:  Deprecated
   Change Controller:  IETF
   Reference:  Section 2.2 of RFC 9864
   Algorithm Analysis Document(s):  [RFC8032]

4.2.  COSE Algorithm Registrations

   IANA has registered the following values in the "COSE Algorithms"
   registry [IANA.COSE] established by [RFC9053] and [RFC9054] and has
   added this document as an additional reference for the registry.

4.2.1.  Fully-Specified COSE Algorithm Registrations

   Name:  ESP256
   Value:  -9
   Description:  ECDSA using P-256 curve and SHA-256
   Capabilities:  [kty]
   Change Controller:  IETF
   Reference:  Section 2.1 of RFC 9864
   Recommended:  Yes

   Name:  ESP384
   Value:  -51
   Description:  ECDSA using P-384 curve and SHA-384
   Capabilities:  [kty]
   Change Controller:  IETF
   Reference:  Section 2.1 of RFC 9864
   Recommended:  Yes

   Name:  ESP512
   Value:  -52
   Description:  ECDSA using P-521 curve and SHA-512
   Capabilities:  [kty]
   Change Controller:  IETF
   Reference:  Section 2.1 of RFC 9864
   Recommended:  Yes

   Name:  ESB256
   Value:  -265
   Description:  ECDSA using BrainpoolP256r1 curve and SHA-256
   Capabilities:  [kty]
   Change Controller:  IETF
   Reference:  Section 2.1 of RFC 9864
   Recommended:  No

   Name:  ESB320
   Value:  -266
   Description:  ECDSA using BrainpoolP320r1 curve and SHA-384
   Capabilities:  [kty]
   Change Controller:  IETF
   Reference:  Section 2.1 of RFC 9864
   Recommended:  No

   Name:  ESB384
   Value:  -267
   Description:  ECDSA using BrainpoolP384r1 curve and SHA-384
   Capabilities:  [kty]
   Change Controller:  IETF
   Reference:  Section 2.1 of RFC 9864
   Recommended:  No

   Name:  ESB512
   Value:  -268
   Description:  ECDSA using BrainpoolP512r1 curve and SHA-512
   Capabilities:  [kty]
   Change Controller:  IETF
   Reference:  Section 2.1 of RFC 9864
   Recommended:  No

   Name:  Ed25519
   Value:  -19
   Description:  EdDSA using the Ed25519 parameter set in Section 5.1 of
      [RFC8032]
   Capabilities:  [kty]
   Change Controller:  IETF
   Reference:  Section 2.2 of RFC 9864
   Recommended:  Yes

   Name:  Ed448
   Value:  -53
   Description:  EdDSA using the Ed448 parameter set in Section 5.2 of
      [RFC8032]
   Capabilities:  [kty]
   Change Controller:  IETF
   Reference:  Section 2.2 of RFC 9864
   Recommended:  Yes

4.2.2.  Deprecated Polymorphic COSE Algorithm Registrations

   IANA has updated the status to "Deprecated" and has added this
   document as a reference for the following registrations.

   Name:  ES256
   Value:  -7
   Description:  ECDSA w/ SHA-256
   Capabilities:  [kty]
   Change Controller:  IETF
   Reference:  [RFC9053] and RFC 9864
   Recommended:  Deprecated

   Name:  ES384
   Value:  -35
   Description:  ECDSA w/ SHA-384
   Capabilities:  [kty]
   Change Controller:  IETF
   Reference:  [RFC9053] and RFC 9864
   Recommended:  Deprecated

   Name:  ES512
   Value:  -36
   Description:  ECDSA w/ SHA-512
   Capabilities:  [kty]
   Change Controller:  IETF
   Reference:  [RFC9053] and RFC 9864
   Recommended:  Deprecated

   Name:  EdDSA
   Value:  -8
   Description:  EdDSA
   Capabilities:  [kty]
   Change Controller:  IETF
   Reference:  [RFC9053] and RFC 9864
   Recommended:  Deprecated

4.3.  Updated Review Instructions for Designated Experts

4.3.1.  JSON Web Signature and Encryption Algorithms

   The review instructions for the designated experts [RFC8126] for the
   "JSON Web Signature and Encryption Algorithms" registry [IANA.JOSE]
   in Section 7.1 of [RFC7518] have been updated to include an
   additional review criterion:

   *  Only fully-specified algorithm identifiers may be registered.
      Polymorphic algorithm identifiers must not be registered.

4.3.2.  COSE Algorithms

   The review instructions for the designated experts [RFC8126] for the
   "COSE Algorithms" registry [IANA.COSE] in Section 10.4 of [RFC9053]
   have been updated to include an additional review criterion:

   *  Only fully-specified algorithm identifiers may be registered.
      Polymorphic algorithm identifiers must not be registered.

4.4.  Defining "Deprecated" and "Prohibited"

   The terms "Deprecated" and "Prohibited" as used by JOSE and COSE
   registrations are currently undefined.  Furthermore, while in
   [RFC7518] JOSE specifies that both "Deprecated" and "Prohibited" can
   be used, in [RFC8152] COSE specifies the use of "Deprecated" but not
   "Prohibited".  (Note that [RFC8152] has been obsoleted by [RFC9052].)
   This section defines these terms for use by both JOSE and COSE IANA
   registrations in a consistent manner, eliminating this potentially
   confusing inconsistency.

   For purposes of use in the "JOSE Implementation Requirements" columns
   in the IANA JOSE registries [IANA.JOSE] and in the "Recommended"
   columns in the IANA COSE registries [IANA.COSE], these terms are
   defined as follows:

   Deprecated
      There is a preferred mechanism to achieve functionality similar to
      that referenced by the identifier; this replacement functionality
      SHOULD be utilized in new deployments in preference to the
      deprecated identifier, unless there exist documented operational
      or regulatory requirements that prevent migration away from the
      deprecated identifier.

   Prohibited
      The identifier and the functionality that it references MUST NOT
      be used.  (Identifiers may be designated as "Prohibited" due to
      security flaws, for instance.)

   For completeness, these definitions bring the set of defined terms
   for use in the "Recommended" columns in the IANA COSE registries
   [IANA.COSE] to "Yes" [RFC8152], "No" [RFC8152], "Filter Only"
   [RFC9054], "Prohibited", and "Deprecated".  This updates the
   definitions of the "Recommended" columns in these registries to be:

   Recommended
      Does the IETF have a consensus recommendation to use the
      algorithm?  The legal values are "Yes", "No", "Filter Only",
      "Prohibited", and "Deprecated".

   The set of defined terms for use in the "JOSE Implementation
   Requirements" columns in the IANA JOSE registries [IANA.JOSE] are
   unchanged.

   Note that the terms "Deprecated" and "Prohibited" have been used with
   a multiplicity of different meanings in various specifications,
   sometimes without actually being defined in those specifications.
   For instance, a variation of the term "Deprecated" is used in the
   title of [RFC8996], but the actual specification text uses the
   terminology "MUST NOT be used".

   The definitions above were chosen because they are consistent with
   all existing registrations in both JOSE and COSE; none will need to
   change.  Furthermore, they are consistent with their existing usage
   in JOSE.  The only net change is to enable a clear distinction
   between "Deprecated" and "Prohibited" in future COSE registrations.

5.  Key Representations

   The key representations for the new fully-specified algorithms
   defined by this specification are the same as those for the
   polymorphic algorithms that they replace, other than the "alg" value,
   if included.  For instance, the representation for a key used with
   the Ed25519 algorithm is the same as that specified in [RFC8037],
   except that the "alg" value would be Ed25519 rather than EdDSA, if
   included.

6.  Notes on Algorithms Not Updated

   Some existing polymorphic algorithms are not updated by this
   specification.  This section discusses why they have not been
   updated.

6.1.  RSA Signing Algorithms

   There are different points of view on whether the RS256, RS384, and
   RS512 algorithms should be considered fully specified or not, because
   they can operate on keys of different sizes.  For instance, they can
   use both 2048- and 4096-bit keys.  The same is true of the PS*
   algorithms.

   This document does not describe or request registration of any fully-
   specified RSA algorithms.  Some RSA signing implementations, such as
   FIPS-compliant Hardware Security Modules (HSMs) [FIPS.140-3] limit
   RSA key parameters to specific values with acceptable security
   characteristics.  This approach could be extended to define fully-
   specified RSA algorithms in the future.

   That said, should it be useful at some point to have RSA algorithm
   identifiers that are specific to particular key characteristics, a
   future specification could always register them.

6.2.  ECDH Key Agreement Algorithms

   This specification does not update the ECDH algorithms, but it
   describes how to potentially do so in the future, if needed.  The
   registered JOSE and COSE ECDH algorithms are polymorphic because they
   do not specify the curve to be used for the ephemeral key.

   Fully-specified versions of these algorithms would specify all
   choices needed, including the KDF and the curve.  For instance, an
   algorithm performing ECDH-ES using the Concat KDF and the P-256 curve
   would be fully specified and could be defined and registered.  While
   this specification does not define and register such replacement
   algorithms, other specifications could do so in the future, if
   desired.

6.3.  HSS/LMS Hash-Based Digital Signature Algorithm

   The HSS-LMS algorithm registered by COSE is polymorphic.  It is
   polymorphic because the algorithm identifier does not specify the
   hash function to be used.  Like ECDH, this specification does not
   register replacement algorithms, but future specifications could do
   so.

7.  Security Considerations

   The security considerations for ECDSA in [RFC7518], for EdDSA in
   [RFC8037], and for ECDSA and EdDSA in [RFC9053] apply.

   The security considerations for preventing cross-protocol attacks
   described in [RFC9459] apply.

   An "attack signature" is a unique pattern or characteristic used to
   identify malicious activity, enabling systems to detect and respond
   to known threats.  The digital signature and key establishment
   algorithms used by software can contribute to an attack signature.
   By varying the identifier used for an algorithm, some software
   systems may attempt to evade rule-based detection and classification.
   Rule-based detection and classification systems may need to update
   their rules to account for fully-specified algorithms.  These systems
   should be aware that writing rules for polymorphic algorithms is more
   difficult, as each variant of the algorithm must be accounted for.
   For example, ES384 in COSE might be used with three different keys,
   each with a different curve.

   A cryptographic key MUST be used with only a single algorithm unless
   the use of the same key with different algorithms is proven secure.
   See [Reuse25519] for an example of such a proof.  As a result, it is
   RECOMMENDED that the algorithm parameter of JSON Web Keys and COSE
   Keys be present, unless there exists some other mechanism for
   ensuring that the key is used as intended.

   In COSE, preventing cross-protocol attacks, such as those described
   in [RFC9459], can be accomplished in two ways:

   1.  Allow only authenticated content encryption (Authenticated
       Encryption with Associated Data (AEAD)) algorithms.

   2.  Bind the potentially unauthenticated content encryption algorithm
       to be used to the key protection algorithm so that different
       content encryption algorithms result in different content
       encryption keys.

   Which choice to use in which circumstances is beyond the scope of
   this specification.

8.  References

8.1.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC7516]  Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
              RFC 7516, DOI 10.17487/RFC7516, May 2015,
              <https://www.rfc-editor.org/info/rfc7516>.

   [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,
              <https://www.rfc-editor.org/info/rfc8037>.

   [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>.

   [RFC9052]  Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Structures and Process", STD 96, RFC 9052,
              DOI 10.17487/RFC9052, August 2022,
              <https://www.rfc-editor.org/info/rfc9052>.

   [RFC9053]  Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053,
              August 2022, <https://www.rfc-editor.org/info/rfc9053>.

8.2.  Informative References

   [FIDO2]    Bradley, J., Jones, M.B., Kumar, A., Lindemann, R.,
              Verrept, J., and D. Waite, "Client to Authenticator
              Protocol (CTAP)", FIDO Alliance Proposed Standard, 14 July
              2025, <https://fidoalliance.org/specs/fido-v2.2-ps-
              20250714/fido-client-to-authenticator-protocol-v2.2-ps-
              20250714.html>.

   [FIPS.140-3]
              NIST, "Security Requirements for Cryptographic Modules",
              NIST FIPS 140-3, DOI 10.6028/NIST.FIPS.140-3, March 2019,
              <https://nvlpubs.nist.gov/nistpubs/FIPS/
              NIST.FIPS.140-3.pdf>.

   [IANA.COSE]
              IANA, "CBOR Object Signing and Encryption (COSE)",
              <https://www.iana.org/assignments/cose/>.

   [IANA.JOSE]
              IANA, "JSON Object Signing and Encryption (JOSE)",
              <https://www.iana.org/assignments/jose/>.

   [OpenID.Discovery]
              Sakimura, N., Bradley, J., Jones, M., and E. Jay, "OpenID
              Connect Discovery 1.0 incorporating errata set 2", 15
              December 2023, <https://openid.net/specs/openid-connect-
              discovery-1_0.html>.

   [Reuse25519]
              Thormarker, E., "On using the same key pair for Ed25519
              and an X25519 based KEM", 23 April 2021,
              <https://eprint.iacr.org/2021/509.pdf>.

   [RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,
              <https://www.rfc-editor.org/info/rfc7518>.

   [RFC8032]  Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
              Signature Algorithm (EdDSA)", RFC 8032,
              DOI 10.17487/RFC8032, January 2017,
              <https://www.rfc-editor.org/info/rfc8032>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8152]  Schaad, J., "CBOR Object Signing and Encryption (COSE)",
              RFC 8152, DOI 10.17487/RFC8152, July 2017,
              <https://www.rfc-editor.org/info/rfc8152>.

   [RFC8414]  Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0
              Authorization Server Metadata", RFC 8414,
              DOI 10.17487/RFC8414, June 2018,
              <https://www.rfc-editor.org/info/rfc8414>.

   [RFC8996]  Moriarty, K. and S. Farrell, "Deprecating TLS 1.0 and TLS
              1.1", BCP 195, RFC 8996, DOI 10.17487/RFC8996, March 2021,
              <https://www.rfc-editor.org/info/rfc8996>.

   [RFC9054]  Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Hash Algorithms", RFC 9054, DOI 10.17487/RFC9054, August
              2022, <https://www.rfc-editor.org/info/rfc9054>.

   [RFC9459]  Housley, R. and H. Tschofenig, "CBOR Object Signing and
              Encryption (COSE): AES-CTR and AES-CBC", RFC 9459,
              DOI 10.17487/RFC9459, September 2023,
              <https://www.rfc-editor.org/info/rfc9459>.

   [WebAuthn] Hodges, J., Ed., Jones, J.C., Ed., Jones, M.B., Ed.,
              Kumar, A., Ed., and E. Lundberg, Ed., "Web Authentication:
              An API for accessing Public Key Credentials - Level 2",
              W3C Recommendation, 8 April 2021,
              <https://www.w3.org/TR/2021/REC-webauthn-2-20210408/>.

Acknowledgements

   The authors thank Mike Bishop, Carsten Bormann, Mohamed Boucadair,
   John Bradley, Tim Bray, Brian Campbell, Deb Cooley, Roman Danyliw,
   Stephen Farrell, Vijay Gurbani, Ilari Liusvaara, Tobias Looker, Neil
   Madden, Kathleen Moriarty, Jeremy O'Donoghue, John Preuß Mattsson,
   Anders Rundgren, Göran Selander, Filip Skokan, Oliver Terbu, Hannes
   Tschofenig, Sean Turner, Éric Vyncke, David Waite, Paul Wouters, and
   Jiankang Yao for their contributions to this specification.

Authors' Addresses

   Michael B. Jones
   Self-Issued Consulting
   Email: michael_b_jones@hotmail.com
   URI:   https://self-issued.info/


   Orie Steele
   Tradeverifyd
   Email: orie@or13.io
