JOSE Working Group
Internet Engineering Task Force (IETF) M.B. Jones
Internet-Draft
Request for Comments: 9864 Self-Issued Consulting
Updates: 7518, 8037, 9053 (if approved) O. Steele
Intended status:
Category: Standards Track Transmute
Expires: 11 November 2025 10 May
ISSN: 2070-1721 September 2025
Fully-Specified
Fully Specified Algorithms for JOSE JSON Object Signing and COSE
draft-ietf-jose-fully-specified-algorithms-13 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 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
fully specified algorithm identifiers. It deprecates those
polymorphic algorithm identifiers.
This specification updates RFC RFCs 7518, RFC 8037, and RFC 9053. It deprecates
polymorphic algorithms defined by RFC RFCs 8037 and RFC 9053 and provides fully-specified
fully specified replacements for them. It adds to the instructions
to designated experts in RFC RFCs 7518 and RFC 9053.
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 an Internet Standards Track document.
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(IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of six months RFC 7841.
Information about the current status of this document, any errata,
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This Internet-Draft will expire on 11 November 2025.
https://www.rfc-editor.org/info/rfc9864.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Notation and Conventions . . . . . . . . . . 4
2. Fully-Specified Fully Specified Digital Signature Algorithm Identifiers . . . 4
2.1. Elliptic Curve Digital Signature Algorithm (ECDSA) . . . 4
2.2. Edwards-Curve Edwards-curve Digital Signature Algorithm (EdDSA) . . . . 5
3. Fully-Specified Fully Specified Encryption . . . . . . . . . . . . . . . . . 6
3.1. Fully-Specified Fully Specified Encryption Algorithms . . . . . . . . . . 7
3.2. Polymorphic Encryption Algorithms . . . . . . . . . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
4.1. JOSE Algorithms Algorithm Registrations . . . . . . . . . . . . . . 8
4.1.1. Fully-Specified Fully Specified JOSE Algorithm Registrations . . . . 8
4.1.2. Deprecated Polymorphic JOSE Algorithm
Registrations . . . . . . . . . . . . . . . . . . . . 8 Registration
4.2. COSE Algorithms Algorithm Registrations . . . . . . . . . . . . . . 9
4.2.1. Fully-Specified Fully Specified COSE Algorithm Registrations . . . . 9
4.2.2. Deprecated Polymorphic COSE Algorithm Registrations . . . . . . . . . . . . . . . . . . . . 11
4.3. Updated Review Instructions for Designated Experts . . . 11
4.3.1. JSON Web Signature and Encryption Algorithms . . . . 11
4.3.2. COSE Algorithms . . . . . . . . . . . . . . . . . . . 12
4.4. Defining Deprecated "Deprecated" and Prohibited . . . . . . . . . . . 12 "Prohibited"
5. Key Representations . . . . . . . . . . . . . . . . . . . . . 13
6. Notes on Algorithms Not Updated . . . . . . . . . . . . . . . 13
6.1. RSA Signing Algorithms . . . . . . . . . . . . . . . . . 14
6.2. ECDH Key Agreement Algorithms . . . . . . . . . . . . . . 14
6.3. HSS/LMS Hash-Based Digital Signature Algorithm . . . . . 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.1. Normative References . . . . . . . . . . . . . . . . . . 15
8.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix A. Document History . . . . . . . . . . . . . . . . . . 18
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
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 EdDSA 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 the 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 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 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 fully specified algorithm identifiers for
registered polymorphic JOSE and COSE algorithms and their parameters,
enabling applications to use only fully-specified 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 Fully Specified Digital Signature Algorithm Identifiers
This section creates fully-specified 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
full-specified.)
fully specified.)
The following fully-specified fully specified COSE ECDSA algorithms are defined by
this specification:
+========+==================+===================+=============+
+========+============+=============================+=============+
| Name | COSE Value | Description | COSE |
| | | | Recommended |
+========+==================+===================+=============+
+========+============+=============================+=============+
| ESP256 | TBD (requested -9 | ECDSA using P-256 curve and | Yes |
| | assignment -9) | curve and SHA-256 | |
+--------+------------------+-------------------+-------------+
+--------+------------+-----------------------------+-------------+
| ESP384 | TBD (requested -51 | ECDSA using P-384 curve and | Yes |
| | assignment -51) | curve and SHA-384 | |
+--------+------------------+-------------------+-------------+
+--------+------------+-----------------------------+-------------+
| ESP512 | TBD (requested -52 | ECDSA using P-521 curve and | Yes |
| | assignment -52) | curve and SHA-512 | |
+--------+------------------+-------------------+-------------+
+--------+------------+-----------------------------+-------------+
| ESB256 | TBD (requested -265 | ECDSA using | No |
| | assignment -265) | BrainpoolP256r1 | No |
| | | curve and SHA-256 | |
+--------+------------------+-------------------+-------------+
+--------+------------+-----------------------------+-------------+
| ESB320 | TBD (requested -266 | ECDSA using | No |
| | assignment -266) | BrainpoolP320r1 | No |
| | | curve and SHA-384 | |
+--------+------------------+-------------------+-------------+
+--------+------------+-----------------------------+-------------+
| ESB384 | TBD (requested -267 | ECDSA using | No |
| | assignment -267) | BrainpoolP384r1 | No |
| | | curve and SHA-384 | |
+--------+------------------+-------------------+-------------+
+--------+------------+-----------------------------+-------------+
| ESB512 | TBD (requested -268 | ECDSA using | No |
| | assignment -268) | BrainpoolP512r1 | No |
| | | curve and SHA-512 | |
+--------+------------------+-------------------+-------------+
+--------+------------+-----------------------------+-------------+
Table 1: ECDSA Algorithm Values
2.2. Edwards-Curve Edwards-curve Digital Signature Algorithm (EdDSA)
[RFC8037] defines a way to use the Edwards-Curve Digital Signature
Algorithm (EdDSA) EdDSA with JOSE JOSE, and [RFC9053] defines
a way to use it with COSE. Both register polymorphic EdDSA algorithm
identifiers.
The following fully-specified fully specified JOSE and COSE EdDSA algorithms are
defined by this specification:
+=======+============+=============+================+=============+
|Name
+=========+=======+=============+=====================+=============+
| Name | COSE Value | Description | JOSE | COSE |
| | Value | | Implementation | Recommended |
| | | | Requirements | |
+=======+============+=============+================+=============+
|Ed25519| TBD
+=========+=======+=============+=====================+=============+
| Ed25519 | -19 | EdDSA using | Optional | Yes |
| | (requested | Ed25519 | | |
| | assignment | curve | | |
+---------+-------+-------------+---------------------+-------------+
| Ed448 | -19) | | | |
+-------+------------+-------------+----------------+-------------+
|Ed448 | TBD -53 | EdDSA using | Optional | Yes |
| | (requested | Ed448 curve | | |
| | assignment | | | |
| | -53) | | | |
+-------+------------+-------------+----------------+-------------+
+---------+-------+-------------+---------------------+-------------+
Table 2: EdDSA Algorithm Values
3. Fully-Specified Fully Specified Encryption
This section describes the construction of fully-specified 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 Encrypt, as described in [RFC9052] and [RFC9053].
Using fully-specified 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 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 value, and the "enc" value MUST specify
all parameters for symmetric encryption. For example, JWE 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-
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. An example of this is that 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, 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 fully specified encryption in COSE, the outer "alg" value
MUST specify all parameters for key establishment establishment, and the inner
"alg" value must specify all parameters for symmetric encryption.
For example, COSE encryption via COSE using an outer "alg" value of A128KW
"A128KW" and an inner "alg" value of A128GCM "A128GCM" uses fully-specified 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- 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 Fully Specified Encryption Algorithms
Many of the registered JOSE and COSE algorithms used for encryption
are already fully-specified. fully specified. This section discusses them.
All the symmetric encryption algorithms registered by [RFC7518] and
[RFC9053] are fully-specified. fully specified. An example of a fully-specified 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 key wrapping with AES GCM algorithms. An
example of a fully-specified 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 Key Encryption with PBES2 algorithms 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 ECDH 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 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 Algorithms Algorithm Registrations
This section registers
IANA has registered the following values in this section in the IANA "JSON Web
Signature and Encryption Algorithms" registry [IANA.JOSE] established
by [RFC7515]. [RFC7518] and has listed this document as an additional reference
for the registry.
4.1.1. Fully-Specified Fully Specified JOSE Algorithm Registrations
*
Algorithm Name: Ed25519
*
Algorithm Description: EdDSA using Ed25519 curve
*
Algorithm Usage Locations: alg
*
JOSE Implementation Requirements: Optional
*
Change Controller: IETF
*
Reference: Section 2.2 of [[ this specification ]]
* RFC 9864
Algorithm Analysis Document(s): [RFC8032]
*
Algorithm Name: Ed448
*
Algorithm Description: EdDSA using Ed448 curve
*
Algorithm Usage Locations: alg
*
JOSE Implementation Requirements: Optional
*
Change Controller: IETF
*
Reference: Section 2.2 of [[ this specification ]]
* RFC 9864
Algorithm Analysis Document(s): [RFC8032]
4.1.2. Deprecated Polymorphic JOSE Algorithm Registrations
The following registration is Registration
IANA has updated to change its the status to
Deprecated.
* "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 [[ this specification ]]
* RFC 9864
Algorithm Analysis Document(s): [RFC8032]
4.2. COSE Algorithms Algorithm Registrations
This section registers
IANA has registered the following values in the IANA "COSE Algorithms"
registry [IANA.COSE]. [IANA.COSE] established by [RFC9053] and [RFC9054] and has
added this document as an additional reference for the registry.
4.2.1. Fully-Specified Fully Specified COSE Algorithm Registrations
*
Name: ESP256
*
Value: TBD (requested assignment -9)
* -9
Description: ECDSA using P-256 curve and SHA-256
*
Capabilities: [kty]
*
Change Controller: IETF
*
Reference: Section 2.1 of [[ this specification ]]
* RFC 9864
Recommended: Yes
*
Name: ESP384
*
Value: TBD (requested assignment -51)
* -51
Description: ECDSA using P-384 curve and SHA-384
*
Capabilities: [kty]
*
Change Controller: IETF
*
Reference: Section 2.1 of [[ this specification ]]
* RFC 9864
Recommended: Yes
*
Name: ESP512
*
Value: TBD (requested assignment -52)
* -52
Description: ECDSA using P-521 curve and SHA-512
*
Capabilities: [kty]
*
Change Controller: IETF
*
Reference: Section 2.1 of [[ this specification ]]
* RFC 9864
Recommended: Yes
*
Name: ESB256
*
Value: TBD (requested assignment -261)
* -265
Description: ECDSA using BrainpoolP256r1 curve and SHA-256
*
Capabilities: [kty]
*
Change Controller: IETF
*
Reference: Section 2.1 of [[ this specification ]]
* RFC 9864
Recommended: No
*
Name: ESB320
*
Value: TBD (requested assignment -262)
* -266
Description: ECDSA using BrainpoolP320r1 curve and SHA-384
*
Capabilities: [kty]
*
Change Controller: IETF
*
Reference: Section 2.1 of [[ this specification ]]
* RFC 9864
Recommended: No
*
Name: ESB384
*
Value: TBD (requested assignment -263)
* -267
Description: ECDSA using BrainpoolP384r1 curve and SHA-384
*
Capabilities: [kty]
*
Change Controller: IETF
*
Reference: Section 2.1 of [[ this specification ]]
* RFC 9864
Recommended: No
*
Name: ESB512
*
Value: TBD (requested assignment -264)
* -268
Description: ECDSA using BrainpoolP512r1 curve and SHA-512
*
Capabilities: [kty]
*
Change Controller: IETF
*
Reference: Section 2.1 of [[ this specification ]]
* RFC 9864
Recommended: No
*
Name: Ed25519
*
Value: TBD (requested assignment -19)
* -19
Description: EdDSA using Ed25519 curve
*
Capabilities: [kty]
*
Change Controller: IETF
*
Reference: Section 2.2 of [[ this specification ]]
* RFC 9864
Recommended: Yes
*
Name: Ed448
*
Value: TBD (requested assignment -53)
* -53
Description: EdDSA using Ed448 curve
*
Capabilities: [kty]
*
Change Controller: IETF
*
Reference: Section 2.2 of [[ this specification ]]
* RFC 9864
Recommended: Yes
4.2.2. Deprecated Polymorphic COSE Algorithm Registrations
The following registrations are
IANA has updated to change their the status to
Deprecated.
* "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 9053
* 9864
Recommended: Deprecated
*
Name: ES384
*
Value: -35
*
Description: ECDSA w/ SHA-384
*
Capabilities: [kty]
*
Change Controller: IETF
*
Reference: [RFC9053] and RFC 9053
* 9864
Recommended: Deprecated
*
Name: ES512
*
Value: -36
*
Description: ECDSA w/ SHA-512
*
Capabilities: [kty]
*
Change Controller: IETF
*
Reference: [RFC9053] and RFC 9053
* 9864
Recommended: Deprecated
*
Name: EdDSA
*
Value: -8
*
Description: EdDSA
*
Capabilities: [kty]
*
Change Controller: IETF
*
Reference: [RFC9053] and RFC 9053
* 9864
Recommended: Deprecated
4.3. Updated Review Instructions for Designated Experts
4.3.1. JSON Web Signature and Encryption Algorithms
IANA is directed to preserve the current reference to RFC 7518, and
to add a reference to this section of this specification.
The review instructions for the designated experts [RFC8126] for the IANA
"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 fully specified algorithm identifiers may be registered.
Polymorphic algorithm identifiers must not be registered.
4.3.2. COSE Algorithms
IANA is directed to preserve the current references to RFC 9053 and
RFC 9054, and to add a reference to this section of this
specification.
The review instructions for the designated experts [RFC8126] for the IANA
"COSE Algorithms" registry [IANA.COSE] in Section 10.4 of [RFC9053]
have been updated to include an additional review criterion:
* Only fully-specified fully specified algorithm identifiers may be registered.
Polymorphic algorithm identifiers must not be registered.
4.4. Defining Deprecated "Deprecated" and Prohibited "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". 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 similar 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, 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 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 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- 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 Elliptic Curve Diffie-Hellman
(ECDH) 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
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, curve
would be fully-specified 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 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 3 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 (AEAD) (Authenticated
Encryption with Associated Data (AEAD)) algorithms.
2. Bind the potentially unauthenticated content encryption algorithm
to be used into 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>.
[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>.
[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., Kumar, A., Lindemann, R., Johan,
J., and D. David, "Client to Authenticator Protocol
(CTAP)", FIDO Alliance Proposed Standard, 28 February
2025, <https://fidoalliance.org/specs/fido-v2.2-ps-
20250228/fido-client-to-authenticator-protocol-v2.2-ps-
20250228.html>.
[FIPS.140-3]
National Institute of Standards and Technology (NIST),
NIST, "Security Requirements for Cryptographic Modules",
NIST FIPS PUB 140-3, 22 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.B., and E. Jay,
"OpenID Connect Discovery 1.0", 1.0 incorporating errata set 2",
15 December 2023,
<https://openid.net/specs/openid-connect-discovery-
1_0.html>. <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", World Wide Web Consortium
(W3C)
W3C Recommendation, 8 April 2021,
<https://www.w3.org/TR/2021/REC-webauthn-2-20210408/>.
Appendix A. Document History
[[ to be removed by the RFC Editor before publication as an RFC ]]
-13
* Applied suggestions by Mike Bishop and Paul Wouters.
-12
* Changed requested COSE assignments for ESP384, ESP512, Ed25519,
and Ed448 due to conflicts with the new ML-DSA assignments.
-11
* Stated in the abstract that the specification deprecates some
polymorphic algorithm identifiers, as suggested by Éric Vyncke.
-10
* Provided a complete list of the Recommended column terms for COSE
registrations, as suggested by Mohamed Boucadair.
* Applied suggestions to improve the exposition received during IESG
review.
-09
* Addressed comments from secdir review by Kathleen Moriarty.
-08
* Updated requested Brainpool algorithm numbers to match those
chosen by Sean Turner.
* Incorporated wording suggestions by Vijay Gurbani.
-07
* Addressed Deb Cooley's Area Director feedback. Specifically:
- Significantly simplified the encryption description.
- Removed the appendix on polymorphic ECDH algorithms.
* Stated that HSS-LMS is not fully specified, as suggested by John
Preuß Mattsson.
-06
* Corrected inconsistencies identified during the 2nd WGLC.
* Added terminology remark about the "cipher suite" and "à la carte"
approaches.
-05
* Applied IANA early review comments.
-04
* Removed ECDH registrations and proposed fully-specified ECDH
algorithm identifiers, per feedback at IETF 120.
* Tightened descriptive text for fully-specified encryption
algorithms.
* Applied John Mattsson's suggestion for the RSA section title.
-03
* Acknowledged contributions made during Working Group Last Call.
* Addressed security considerations feedback from WGLC.
* Made COSE Recommended status for Ed25519 and Ed448 "yes".
* Registered COSE algorithms for using Brainpool curves with ECDSA.
* Removed text on KEMs, since currently registered algorithms don't
use them.
* Enabled use of fully-specified ECDH algorithms.
* Defined the terms "Deprecated" and "Prohibited" for both JOSE and
COSE registrations.
-02
* Expanded references for KEMs.
* Added example of a fully-specified KEM.
-01
* Included additional instructions for IANA.
* Added text on KEMs and Encapsulated keys.
* Added the section Fully-Specified Computations Using Multiple
Algorithms.
-00
* Created initial working group version based on draft-jones-jose-
fully-specified-algorithms-02.
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, John Preuß Mattsson, 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
Transmute
Email: orie@transmute.industries