Fully-Specified Algorithms for JOSE and COSE
draft-ietf-jose-fully-specified-algorithms-06
| Document | Type | Active Internet-Draft (jose WG) | |
|---|---|---|---|
| Authors | Michael B. Jones , Orie Steele | ||
| Last updated | 2025-01-09 (Latest revision 2024-10-21) | ||
| Replaces | draft-jones-jose-fully-specified-algorithms | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | |||
| Additional resources |
GitHub Repository
Mailing list discussion |
||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Karen O'Donoghue | ||
| Shepherd write-up | Show Last changed 2024-12-17 | ||
| IESG | IESG state | AD Evaluation::Revised I-D Needed | |
| Action Holders | |||
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | Deb Cooley | ||
| Send notices to | kodonog@pobox.com |
draft-ietf-jose-fully-specified-algorithms-06
JOSE Working Group M.B. Jones
Internet-Draft Self-Issued Consulting
Updates: 7518, 8037, 8152, 9053 (if approved) O. Steele
Intended status: Standards Track Transmute
Expires: 24 April 2025 21 October 2024
Fully-Specified Algorithms for JOSE and COSE
draft-ietf-jose-fully-specified-algorithms-06
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 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 24 April 2025.
Copyright Notice
Copyright (c) 2024 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.
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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 . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Notation and Conventions . . . . . . . . . . 4
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) . . . . 5
3. Fully-Specified Encryption . . . . . . . . . . . . . . . . . 6
3.1. Fully-Specified Computations Using Multiple Algorithms . 6
3.2. Analysis of Modes of Encryption . . . . . . . . . . . . . 6
3.2.1. Direct Encryption . . . . . . . . . . . . . . . . . . 7
3.2.2. Key Establishment with Direct Encryption . . . . . . 8
3.2.3. Two-Layer Encryption . . . . . . . . . . . . . . . . 11
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
4.1. JOSE Algorithms Registrations . . . . . . . . . . . . . . 14
4.1.1. Fully-Specified JOSE Algorithm Registrations . . . . 14
4.1.2. Deprecated Polymorphic JOSE Algorithm
Registrations . . . . . . . . . . . . . . . . . . . . 14
4.2. COSE Algorithms Registrations . . . . . . . . . . . . . . 15
4.2.1. Fully-Specified COSE Algorithm Registrations . . . . 15
4.2.2. Deprecated Polymorphic COSE Algorithm
Registrations . . . . . . . . . . . . . . . . . . . . 16
4.3. Updated Review Instructions for Designated Experts . . . 17
4.3.1. JSON Web Signature and Encryption Algorithms . . . . 17
4.3.2. COSE Algorithms . . . . . . . . . . . . . . . . . . . 18
4.4. Defining Deprecated and Prohibited . . . . . . . . . . . 18
5. Key Representations . . . . . . . . . . . . . . . . . . . . . 19
6. Notes on Algorithms Not Updated . . . . . . . . . . . . . . . 19
6.1. RSA Signing Algorithms . . . . . . . . . . . . . . . . . 19
6.2. ECDH Key Agreement Algorithms . . . . . . . . . . . . . . 20
7. Security Considerations . . . . . . . . . . . . . . . . . . . 20
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
8.1. Normative References . . . . . . . . . . . . . . . . . . 20
8.2. Informative References . . . . . . . . . . . . . . . . . 21
Appendix A. Inventory of Polymorphic ECDH Algorithms . . . . . . 23
A.1. Polymorphic ECDH JOSE Algorithms . . . . . . . . . . . . 23
A.2. Polymorphic ECDH COSE Algorithms . . . . . . . . . . . . 24
Appendix B. Document History . . . . . . . . . . . . . . . . . . 26
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
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1. Introduction
The IANA algorithm registries for JOSE [IANA.JOSE] and COSE
[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),
hash functions, etc. Examples are RS256 and ES256K in both JOSE
and 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 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.
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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. 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.
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 ECDSA algorithms are defined:
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+========+==================+===================+=============+
| 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 | |
+--------+------------------+-------------------+-------------+
| ESB256 | TBD (requested | ECDSA using | No |
| | assignment -261) | BrainpoolP256r1 | |
| | | curve and SHA-256 | |
+--------+------------------+-------------------+-------------+
| ESB320 | TBD (requested | ECDSA using | No |
| | assignment -262) | BrainpoolP320r1 | |
| | | curve and SHA-384 | |
+--------+------------------+-------------------+-------------+
| ESB384 | TBD (requested | ECDSA using | No |
| | assignment -263) | BrainpoolP384r1 | |
| | | curve and SHA-384 | |
+--------+------------------+-------------------+-------------+
| ESB512 | TBD (requested | ECDSA using | No |
| | assignment -264) | BrainpoolP512r1 | |
| | | 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 EdDSA algorithms are
defined:
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+=======+============+=============+================+=============+
|Name | COSE Value | Description | JOSE | COSE |
| | | | Implementation | Recommended |
| | | | Requirements | |
+=======+============+=============+================+=============+
|Ed25519| TBD | EdDSA using | Optional | Yes |
| | (requested | Ed25519 | | |
| | assignment | curve | | |
| | -50) | | | |
+-------+------------+-------------+----------------+-------------+
|Ed448 | TBD | EdDSA using | Optional | Yes |
| | (requested | Ed448 curve | | |
| | assignment | | | |
| | -51) | | | |
+-------+------------+-------------+----------------+-------------+
Table 2: EdDSA Algorithm Values
3. Fully-Specified Encryption
This section describes the construction of fully-specified encryption
algorithm identifiers in the context of existing the JOSE and COSE
encryption schemes JSON Web Encryption (JWE) as described in
[RFC7516] and COSE Encrypt as described in [RFC9052].
3.1. Fully-Specified Computations Using Multiple Algorithms
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. The
following sections describe how to fully specify encryption
algorithms when multiple algorithms are used in the computation.
3.2. Analysis of Modes of Encryption
JOSE and COSE support several modes of encryption. Although the
terminology sometimes differs between JOSE and COSE, both support
these encryption modes:
* Direct Encryption - A symmetric cryptographic operation.
* Key Establishment with Direct Encryption - An asymmetric
cryptographic operation to derive a shared secret, key derivation
and then a symmetric cryptographic operation.
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* Two-Layer Encryption - A content encryption key is protected
(multiple possible ways), then content encryption or decryption is
performed using the protected content encryption key.
Mode complexity creates the following risks:
* The combination of chosen algorithms might not be implemented by
the receiver.
* The combination of chosen algorithms might not be aligned in terms
of strength.
* Underspecified or implicit parameters could lead to exploitable
faults in implementations, for example, cross-curve Elliptic Curve
Diffie-Hellman (ECDH) between P-256 and P-384 or X25519.
* Alternative algorithms at a component layer, such as symmetric key
encryption, might provide different security properties, for
example, "A128GCM" vs. "A128CBC-HS256".
While this specification provides a definition of what fully-
specified encryption algorithm identifiers are for both JOSE and
COSE, including examples, it does not deprecate any polymorphic
encryption algorithms, since replacements for them are not provided
by this specification.
The following sections describe what fully specified means for each
mode.
3.2.1. Direct Encryption
Symmetric encryption algorithms generally satisfy the following
interface:
secret_key = key_generation(algorithm_identifier)
ciphertext = encrypt(plaintext, secret_key)
plaintext = decrypt(ciphertext, secret_key)
Depending on the algorithm, additional parameters such as Additional
Authenticated Data (AAD) or Initialization Vector (IV) might be
required.
In the special case where the plaintext is a content encryption key,
to be used with a subsequent symmetric encryption algorithm, such a
symmetric encryption algorithm is referred to as a key wrapping
algorithm and the secret_key is referred to as a key wrapping key.
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An example of a fully-specified symmetric encryption algorithm is
"A128GCM" (AES GCM using 128-bit key).
An example of a fully-specified key wrapping algorithm is "A128KW"
(AES Key Wrap using 128-bit key).
A symmetric encryption algorithm is fully specified when it satisfies
the interface above, and depends only on the parameters to the
encrypt and decrypt operations.
Direct Encryption and Key Wrapping algorithms encode the primary
symmetric key parameter (key length) in the algorithm identifier.
In JOSE and COSE, all currently registered Direct Encryption and Key
Wrapping algorithms are fully specified.
Example of a decoded JWE Protected Header, for Direct Encryption:
{
"alg": "dir",
"enc": "A128GCM",
...
}
Example of a decoded JWE Protected Header, for Key Wrapping:
{
"alg": "A128KW",
"enc": "A128GCM",
...
}
3.2.2. Key Establishment with Direct Encryption
Key establishment with direct encryption algorithms generally satisfy
the following interface:
private_key, public_key = key_generation(algorithm_identifier)
ciphertext = encrypt(plaintext, public_key)
plaintext = decrypt(ciphertext, private_key)
Depending on the symmetric algorithm, additional parameters such as
Additional Authenticated Data (AAD) or Initialization Vector (IV)
might be required.
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Although JOSE and COSE encode this type of encryption differently,
both rely on a symmetric key derived from an asymmetric key. An
algorithm called a key derivation function (KDF) is applied between
key establishment and symmetric encryption.
Key establishment algorithms often rely on an asymmetric
cryptographic operation whereby a public and a private key are used
to produce a shared secret, which can be combined with a KDF to
produce a symmetric key. The process of producing a shared secret is
key type specific, and is different for elliptic curves, RSA, and
lattice-based algorithms.
Elliptic Curve Diffie-Hellman (ECDH) is used to produce a shared
secret with elliptic curve-based keys as follows:
private_key1, public_key1 = key_generation(algorithm_identifier)
private_key2, public_key2 = key_generation(algorithm_identifier)
shared_secret = derive_shared_secret(public_key1, private_key2)
shared_secret = derive_shared_secret(public_key2, private_key1)
An algorithm called a Key Encapsulation Mechanism (KEM) can be used
to provide a common interface for deriving shared secrets, regardless
of key type. For examples of the use of KEMs, see
[I-D.ietf-lamps-rfc5990bis] and [I-D.ietf-lamps-cms-kemri]. Key
encapsulation algorithms generally satisfy the following interface:
private_key, public_key = key_generation(algorithm_identifier)
ciphertext, shared_secret = encapsulate(public_key)
shared_secret = deencapsulate(ciphertext, private_key)
When using Key Establishment with Direct Encryption, the ciphertext
is not only the output of symmetric encryption, but also includes all
parameters necessary for the recipient to decrypt the ciphertext.
Encrypted content encryption keys are not produced by fully-specified
Key Establishment with Direct Encryption algorithms.
In JOSE, the KDF algorithm is "Concat KDF" and is an implicit
parameter of the key establishment algorithm. In JOSE and COSE, key
establishment algorithms have historically been generic to a key type
including all its mandatory parameters. For example, "ECDH-ES"
establishes a shared secret, and then through the use of a KDF, a
content encryption key, for keys based on elliptic curves. However,
the mandatory parameters of the public key and private key need be
the same in the context of the key type.
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For example, when using ECDH-ES with secp256r1 (P-256) to establish a
shared secret, the ECDH algorithm is a function of an ephemeral and a
static key, which need to be of the same key type, and having the
same parameters, in this case, the curve parameter.
To successfully encrypt to a recipient, a sender needs to possess the
recipient's key (which contains the curve parameter) and know the
recipient's supported algorithms. In JOSE and COSE, key
representations can support communicating the algorithm that a
recipient supports for a given key. It is considered a best practice
to only use a key with one algorithm.
Example of a decoded JWE Protected Header, for Key Establishment with
Direct Encryption:
{
"alg":"ECDH-ES",
"enc":"A128GCM",
...
}
Despite containing both the key establishment algorithm (with an
implicit KDF) and the symmetric encryption algorithm, the example
above is not fully specified. To make a Key Establishment with
Direct Encryption algorithm fully specified, all essential parameters
need to be encoded in the algorithm identifiers. In the example
above, the missing explicit parameters are curve name and KDF name.
If the KDF requires additional parameters, they also need to be
present.
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 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 convey fully-specified Key Establishment with Direct Encryption in
JOSE, the "alg" value MUST specify all essential parameters for key
establishment or derive some of them from the accompanying "enc"
value and the "enc" value MUST specify all essential parameters for
symmetric encryption. For example, an "alg" value specifiying ECDH-
ES using P-256 and Concat-KDF and an "enc" value of "A128GCM".
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To convey fully-specified Key Establishment with Direct Encryption in
COSE, the outer "alg" value MUST specify all essential parameters for
key establishment and the inner "alg" value must specify all
essential parameters for symmetric encryption. For example, an outer
"alg" value specifying ECDH-ES using P-256 and HKDF SHA-256 with
128-bit output and an inner "alg" value specifying A128GCM.
3.2.3. Two-Layer Encryption
This section describes Two-Layer Encryption in both JOSE and COSE.
Each defines multiple ways that a content encryption key can be
produced and protected, then later used to decrypt or encrypt
content.
This specification uses the term "Two-Layer Encryption" to refer to
what JOSE describes as "Key Encryption" and "Key Agreement with Key
Wrapping", and what COSE describes as "Key Transport" and "Key
Agreement with Key Wrap".
A distinguishing characteristic of Two-Layer Encryption schemes is
that multiple recipients can perform decryptions, using a wide range
of algorithms, and that encrypted content encryption keys are always
present.
In RSA-OAEP, the content encryption key is encrypted using an
asymmetric cryptographic operation. When Key Wrapping without any
key establishment is used, the content encryption key is encrypted
using a symmetric cryptographic operation (key wrap). How the
content encryption key is generated is out of scope for this
discussion.
Key wrapping algorithms generally satisfy the following interface:
key_encryption_key = \
key_generation(algorithm_identifier)
encrypted_content_encryption_key = \
encrypt(content_encryption_key, key_encryption_key)
content_encryption_key = \
decrypt(encrypted_content_encryption_key, key_encryption_key)
When Key Establishment with Key Wrapping is used, the content
encryption key is protected with Key Wrapping, where the Key
Encryption Key is derived from an asymmetric cryptographic operation
and a key derivation function.
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Key Establishment with Key Wrapping algorithms generally satisfy the
following interface:
private_key, public_key = key_generation(algorithm_identifier)
# ignoring ephemeral/static vs. static/static, etc.
key_encryption_key = \
key_establishment(public_key, private_key)
encrypted_content_encryption_key = \
encrypt(content_encryption_key, key_encryption_key)
content_encryption_key = \
decrypt(encrypted_content_encryption_key, key_encryption_key)
The interface above is consistent with Key Establishment with Direct
Encryption. The process of deriving a shared secret and content
encryption key is specific to the asymmetric key type used. The
difference is that instead of using the derived content encryption
key directly, two-layer encryption always uses a key encryption key,
and protects the content encryption key.
Regardless of how a Two-Layer Encryption scheme protects the content
encryption key, content encryption algorithms generally satisfy the
following interface:
content_encryption_key = \
unwrap or establish and unwrap or key transport...
ciphertext = encrypt(plaintext, content_encryption_key)
plaintext = decrypt(ciphertext, content_encryption_key)
Depending on the content encryption algorithm, additional parameters
such as Additional Authenticated Data (AAD) and/or an Initialization
Vector (IV) might be required.
Although JOSE and COSE encode Two-Layer Encryptions differently, both
rely on a protected content encryption key. The content encryption
key is protected using Key Wrapping directly, or through Key
Establishment and then Key Wrapping, or Key Transport, or Key
Encryption.
When using Two-Layer Encryption, the output of symmetric encryption
includes the ciphertext and is accompanied by all parameters
necessary for the recipient to decrypt the ciphertext, including
parameters for use with the key establishment algorithm, such as
ephemeral or encapsulated keys, any required key derivation functions
and their parameters and the key wrapping algorithm. Encrypted
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content encryption keys are always present when Two-Layer Encryption
is used. Parameters accompanying the ciphertext can include an
Initialization Vector (IV), an Authentication Tag, and Additional
Authenticated Data (AAD). Two-Layer Encryption is often used for
encrypting the same plaintext to multiple recipients, in contrast
with other modes that can only be used to encrypt to a single
recipient.
Example of a decoded JWE Protected Header for Key Encryption with RSA
OAEP and Content Encryption using AES_128_CBC_HMAC_SHA_256:
{
"alg": "RSA-OAEP-256",
"enc": "A128CBC-HS256",
...
}
Example of a decoded JWE Protected Header for Key Agreement using
ECDH-ES with key wrapping and Content Encryption using AES GCM:
{
"alg": "ECDH-ES+A128KW",
"enc": "A128GCM",
...
}
However, despite containing both the key establishment algorithm and
a content encryption algorithm, the second example above is not fully
specified. In this example, the missing parameter is the curve name
for the ephemeral key used for key agreement.
To convey fully-specified Two-Layer Encryption in JOSE, the "alg"
value MUST specify all essential parameters for key protection or
derive them from the accompanying "enc" value and the "enc" value
MUST be fully specified, specifying all essential parameters for
symmetric encryption. For example, ECDH-ES using Concat KDF and
P-256 and "A128KW" key wrapping used with AES-GCM.
To convey fully-specified Two-Layer Encryption in COSE, the outer
"alg" value MUST specify all essential parameters for key protection
and the inner "alg" value MUST be fully specified, specifying all
essential parameters for symmetric encryption. For example, ECDH-ES
using P-256 w/ HKDF and AES Key Wrap w/ 128-bit key used with AES-
GCM.
In COSE, preventing cross-mode attacks, such as those described in
[RFC9459], can be accomplished in two ways: (1) Allow only
authenticated content encryption algorithms. (2) Bind the the
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potentially unauthenticated content encryption algorithm to be used
into 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.
Fully-specified Two-Layer Encryption algorithms enable the sender and
receiver to agree on all mandatory security parameters. They also
enable a protocol to specify an allow list of algorithm combinations
that does not include polymorphic combinations, such as cross-curve
key establishment, cross-mode symmetric encryption, or mismatched KDF
size to symmetric key scenarios.
4. IANA Considerations
4.1. JOSE Algorithms Registrations
This section registers the following values in the IANA "JSON Web
Signature and Encryption Algorithms" registry [IANA.JOSE] established
by [RFC7515].
4.1.1. Fully-Specified JOSE Algorithm Registrations
* Algorithm Name: Ed25519
* Algorithm Description: EdDSA using Ed25519 curve
* Algorithm Usage Locations: alg
* JOSE Implementation Requirements: Optional
* Change Controller: IETF
* 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: IETF
* Reference: Section 2.2 of [[ this specification ]]
* Algorithm Analysis Document(s): [RFC8032]
4.1.2. Deprecated Polymorphic JOSE Algorithm Registrations
The following registration is updated to change its status to
Deprecated.
* Algorithm Name: EdDSA
* Algorithm Description: EdDSA signature algorithms
* Algorithm Usage Locations: alg
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* JOSE Implementation Requirements: Deprecated
* Change Controller: IETF
* Reference: Section 2.2 of [[ this specification ]]
* Algorithm Analysis Document(s): [RFC8032]
4.2. COSE Algorithms Registrations
This section registers the following values in the IANA "COSE
Algorithms" registry [IANA.COSE].
4.2.1. Fully-Specified COSE Algorithm Registrations
* Name: ESP256
* Value: TBD (requested assignment -9)
* Description: ECDSA using P-256 curve and SHA-256
* Capabilities: [kty]
* Change Controller: IETF
* Reference: Section 2.1 of [[ this specification ]]
* Recommended: Yes
* Name: ESP384
* Value: TBD (requested assignment -48)
* Description: ECDSA using P-384 curve and SHA-384
* Capabilities: [kty]
* Change Controller: IETF
* Reference: Section 2.1 of [[ this specification ]]
* Recommended: Yes
* Name: ESP512
* Value: TBD (requested assignment -49)
* Description: ECDSA using P-521 curve and SHA-512
* Capabilities: [kty]
* Change Controller: IETF
* Reference: Section 2.1 of [[ this specification ]]
* Recommended: Yes
* Name: ESB256
* Value: TBD (requested assignment -261)
* Description: ECDSA using BrainpoolP256r1 curve and SHA-256
* Capabilities: [kty]
* Change Controller: IETF
* Reference: Section 2.1 of [[ this specification ]]
* Recommended: No
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* Name: ESB320
* Value: TBD (requested assignment -262)
* Description: ECDSA using BrainpoolP320r1 curve and SHA-384
* Capabilities: [kty]
* Change Controller: IETF
* Reference: Section 2.1 of [[ this specification ]]
* Recommended: No
* Name: ESB384
* Value: TBD (requested assignment -263)
* Description: ECDSA using BrainpoolP384r1 curve and SHA-384
* Capabilities: [kty]
* Change Controller: IETF
* Reference: Section 2.1 of [[ this specification ]]
* Recommended: No
* Name: ESB512
* Value: TBD (requested assignment -264)
* Description: ECDSA using BrainpoolP512r1 curve and SHA-512
* Capabilities: [kty]
* Change Controller: IETF
* Reference: Section 2.1 of [[ this specification ]]
* Recommended: No
* Name: Ed25519
* Value: TBD (requested assignment -50)
* Description: EdDSA using Ed25519 curve
* Capabilities: [kty]
* Change Controller: IETF
* Reference: Section 2.2 of [[ this specification ]]
* Recommended: Yes
* Name: Ed448
* Value: TBD (requested assignment -51)
* Description: EdDSA using Ed448 curve
* Capabilities: [kty]
* Change Controller: IETF
* Reference: Section 2.2 of [[ this specification ]]
* Recommended: Yes
4.2.2. Deprecated Polymorphic COSE Algorithm Registrations
The following registrations are updated to change their status to
Deprecated.
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* Name: ES256
* Value: -7
* Description: ECDSA w/ SHA-256
* Capabilities: [kty]
* Change Controller: IETF
* Reference: RFC 9053
* Recommended: Deprecated
* Name: ES384
* Value: -35
* Description: ECDSA w/ SHA-384
* Capabilities: [kty]
* Change Controller: IETF
* Reference: RFC 9053
* Recommended: Deprecated
* Name: ES512
* Value: -36
* Description: ECDSA w/ SHA-512
* Capabilities: [kty]
* Change Controller: IETF
* Reference: RFC 9053
* Recommended: Deprecated
* Name: EdDSA
* Value: -8
* Description: EdDSA
* Capabilities: [kty]
* Change Controller: IETF
* Reference: RFC 9053
* 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 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:
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* Only 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 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 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 [RFC9053] did not carry the definitions of
the "Recommended" registry columns forward, so [RFC8152] remains
definitive in this regard.) 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 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 requirments 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.)
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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 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
The working group has discussed some existing algorithms that are not
updated by this specification. This section discusses why they have
not been updated.
6.1. RSA Signing Algorithms
The working group has discussed 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.
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6.2. ECDH Key Agreement Algorithms
As discussed in Appendix A, the working group decided not to update
the Elliptic Curve Diffie-Hellman (ECDH) algorithms at this time, but
to describe how to potentially do so in the future, if needed.
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-mode attacks
described in [RFC9459] apply.
A cryptographic key SHOULD 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 the key is used as intended.
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>.
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[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., Hodges, J., Jones, M., Kumar, A., Lindemann,
R., and J. Johan, "Client to Authenticator Protocol
(CTAP)", FIDO Alliance Proposed Standard, 21 June 2022,
<https://fidoalliance.org/specs/fido-v2.1-ps-20210615/
fido-client-to-authenticator-protocol-v2.1-ps-errata-
20220621.html>.
[FIPS.140-3]
National Institute of Standards and Technology (NIST),
"Security Requirements for Cryptographic Modules",
FIPS PUB 140-3, 22 March 2019,
<https://nvlpubs.nist.gov/nistpubs/FIPS/
NIST.FIPS.140-3.pdf>.
[I-D.ietf-lamps-cms-kemri]
Housley, R., Gray, J., and T. Okubo, "Using Key
Encapsulation Mechanism (KEM) Algorithms in the
Cryptographic Message Syntax (CMS)", Work in Progress,
Internet-Draft, draft-ietf-lamps-cms-kemri-08, 6 February
2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
lamps-cms-kemri-08>.
[I-D.ietf-lamps-rfc5990bis]
Housley, R. and S. Turner, "Use of the RSA-KEM Algorithm
in the Cryptographic Message Syntax (CMS)", Work in
Progress, Internet-Draft, draft-ietf-lamps-rfc5990bis-10,
30 July 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-lamps-rfc5990bis-10>.
[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/>.
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[OpenID.Discovery]
Sakimura, N., Bradley, J., Jones, M.B., and E. Jay,
"OpenID Connect Discovery 1.0", 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>.
[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>.
[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., Jones, J.C., Jones, M.B., 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,
<https://www.w3.org/TR/2021/REC-webauthn-2-20210408/>.
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Appendix A. Inventory of Polymorphic ECDH Algorithms
The working group assembled the following inventory of registered
polymorphic Elliptic Curve Diffie-Hellman (ECDH) JOSE and COSE
algorithms with the goal of understanding what registering fully-
specified ECDH algorithms to replace them would entail. While there
was not an appetite in the working group to register these
replacement algorithms at this time, this inventory documents how to
do so, should others wish to register some or all of the replacements
in the future.
A.1. Polymorphic ECDH JOSE Algorithms
These registered JOSE algorithms are polymorphic, because they do not
include the curve name in the algorithm to be used with the ephemeral
key:
+================+================================================+
| Name | Description |
+================+================================================+
| ECDH-ES | ECDH-ES using Concat KDF |
+----------------+------------------------------------------------+
| ECDH-ES+A128KW | ECDH-ES using Concat KDF and "A128KW" wrapping |
+----------------+------------------------------------------------+
| ECDH-ES+A192KW | ECDH-ES using Concat KDF and "A192KW" wrapping |
+----------------+------------------------------------------------+
| ECDH-ES+A256KW | ECDH-ES using Concat KDF and "A256KW" wrapping |
+----------------+------------------------------------------------+
Table 3: Polymorphic ECDH JOSE Algorithms
Descriptions of fully-specified JOSE versions of these algorithms
using combinations discussed by the working group that could be
registered by future specifications are:
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+===========================================================+
| Description |
+===========================================================+
| ECDH-ES using Concat KDF and P-256 |
+-----------------------------------------------------------+
| ECDH-ES using Concat KDF and P-384 |
+-----------------------------------------------------------+
| ECDH-ES using Concat KDF and P-521 |
+-----------------------------------------------------------+
| ECDH-ES using Concat KDF and X25519 |
+-----------------------------------------------------------+
| ECDH-ES using Concat KDF and X448 |
+-----------------------------------------------------------+
| ECDH-ES using Concat KDF and P-256 and "A128KW" wrapping |
+-----------------------------------------------------------+
| ECDH-ES using Concat KDF and X25519 and "A128KW" wrapping |
+-----------------------------------------------------------+
| ECDH-ES using Concat KDF and P-384 and "A192KW" wrapping |
+-----------------------------------------------------------+
| ECDH-ES using Concat KDF and P-521 and "A256KW" wrapping |
+-----------------------------------------------------------+
| ECDH-ES using Concat KDF and X448 and "A256KW" wrapping |
+-----------------------------------------------------------+
Table 4: Fully-Specified ECDH JOSE Algorithms
A.2. Polymorphic ECDH COSE Algorithms
These registered COSE algorithms are likewise polymorphic, because
they do not include the curve name in the algorithm to be used with
the ephemeral key or the static key:
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+====================+==========================================+
| Name | Description |
+====================+==========================================+
| ECDH-ES + HKDF-256 | ECDH-ES w/ HKDF -- generate key directly |
+--------------------+------------------------------------------+
| ECDH-ES + HKDF-512 | ECDH-ES w/ HKDF -- generate key directly |
+--------------------+------------------------------------------+
| ECDH-SS + HKDF-256 | ECDH-SS w/ HKDF -- generate key directly |
+--------------------+------------------------------------------+
| ECDH-SS + HKDF-512 | ECDH-SS w/ HKDF -- generate key directly |
+--------------------+------------------------------------------+
| ECDH-ES + A128KW | ECDH-ES w/ HKDF and AES Key Wrap w/ |
| | 128-bit key |
+--------------------+------------------------------------------+
| ECDH-ES + A192KW | ECDH-ES w/ HKDF and AES Key Wrap w/ |
| | 192-bit key |
+--------------------+------------------------------------------+
| ECDH-ES + A256KW | ECDH-ES w/ HKDF and AES Key Wrap w/ |
| | 256-bit key |
+--------------------+------------------------------------------+
| ECDH-SS + A128KW | ECDH-SS w/ HKDF and AES Key Wrap w/ |
| | 128-bit key |
+--------------------+------------------------------------------+
| ECDH-SS + A192KW | ECDH-SS w/ HKDF and AES Key Wrap w/ |
| | 192-bit key |
+--------------------+------------------------------------------+
| ECDH-SS + A256KW | ECDH-SS w/ HKDF and AES Key Wrap w/ |
| | 256-bit key |
+--------------------+------------------------------------------+
Table 5: Polymorphic ECDH COSE Algorithms
Descriptions of fully-specified COSE versions of these algorithms
using combinations discussed by the working group that could be
registered by future specifications are:
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+==============================================================+
| Description |
+==============================================================+
| ECDH-ES using P-256 w/ HKDF -- generate key directly |
+--------------------------------------------------------------+
| ECDH-ES using X25519 w/ HKDF -- generate key directly |
+--------------------------------------------------------------+
| ECDH-ES using P-521 w/ HKDF -- generate key directly |
+--------------------------------------------------------------+
| ECDH-ES using X448 w/ HKDF -- generate key directly |
+--------------------------------------------------------------+
| ECDH-SS using P-256 w/ HKDF -- generate key directly |
+--------------------------------------------------------------+
| ECDH-SS using X25519 w/ HKDF -- generate key directly |
+--------------------------------------------------------------+
| ECDH-SS using P-521 w/ HKDF -- generate key directly |
+--------------------------------------------------------------+
| ECDH-SS using X448 w/ HKDF -- generate key directly |
+--------------------------------------------------------------+
| ECDH-ES using P-256 w/ HKDF and AES Key Wrap w/ 128-bit key |
+--------------------------------------------------------------+
| ECDH-ES using X25519 w/ HKDF and AES Key Wrap w/ 128-bit key |
+--------------------------------------------------------------+
| ECDH-ES using P-384 w/ HKDF and AES Key Wrap w/ 192-bit key |
+--------------------------------------------------------------+
| ECDH-ES using P-521 w/ HKDF and AES Key Wrap w/ 256-bit key |
+--------------------------------------------------------------+
| ECDH-ES using X448 w/ HKDF and AES Key Wrap w/ 256-bit key |
+--------------------------------------------------------------+
| ECDH-SS using P-256 w/ HKDF and AES Key Wrap w/ 128-bit key |
+--------------------------------------------------------------+
| ECDH-SS using X25519 w/ HKDF and AES Key Wrap w/ 128-bit key |
+--------------------------------------------------------------+
| ECDH-SS using P-384 w/ HKDF and AES Key Wrap w/ 192-bit key |
+--------------------------------------------------------------+
| ECDH-SS using P-521 w/ HKDF and AES Key Wrap w/ 256-bit key |
+--------------------------------------------------------------+
| ECDH-SS using X448 w/ HKDF and AES Key Wrap w/ 256-bit key |
+--------------------------------------------------------------+
Table 6: Fully-Specified ECDH COSE Algorithms
Appendix B. Document History
[[ to be removed by the RFC Editor before publication as an RFC ]]
-06
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* 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.
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* 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 Carsten Bormann, John Bradley, Tim Bray, Brian
Campbell, Stephen Farrell, Ilari Liusvaara, Tobias Looker, Neil
Madden, John Mattsson, Jeremy O'Donoghue, Anders Rundgren, Göran
Selander, Filip Skokan, Oliver Terbu, Hannes Tschofenig, and David
Waite 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
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