JOSE Working Group M. Jones
Internet-Draft Microsoft
Intended status: Standards Track October 15, 2012
Expires: April 18, 2013
JSON Web Algorithms (JWA)
draft-ietf-jose-json-web-algorithms-06
Abstract
The JSON Web Algorithms (JWA) specification enumerates cryptographic
algorithms and identifiers to be used with the JSON Web Signature
(JWS), JSON Web Encryption (JWE), and JSON Web Key (JWK)
specifications.
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
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This Internet-Draft will expire on April 18, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Notational Conventions . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Terms Incorporated from the JWS Specification . . . . . . 4
2.2. Terms Incorporated from the JWE Specification . . . . . . 5
2.3. Terms Incorporated from the JWK Specification . . . . . . 6
2.4. Defined Terms . . . . . . . . . . . . . . . . . . . . . . 7
3. Cryptographic Algorithms for JWS . . . . . . . . . . . . . . . 7
3.1. "alg" (Algorithm) Header Parameter Values for JWS . . . . 7
3.2. MAC with HMAC SHA-256, HMAC SHA-384, or HMAC SHA-512 . . . 8
3.3. Digital Signature with RSA SHA-256, RSA SHA-384, or
RSA SHA-512 . . . . . . . . . . . . . . . . . . . . . . . 9
3.4. Digital Signature with ECDSA P-256 SHA-256, ECDSA
P-384 SHA-384, or ECDSA P-521 SHA-512 . . . . . . . . . . 10
3.5. Using the Algorithm "none" . . . . . . . . . . . . . . . . 12
3.6. Additional Digital Signature/MAC Algorithms and
Parameters . . . . . . . . . . . . . . . . . . . . . . . . 12
4. Cryptographic Algorithms for JWE . . . . . . . . . . . . . . . 12
4.1. "alg" (Algorithm) Header Parameter Values for JWE . . . . 12
4.2. "enc" (Encryption Method) Header Parameter Values for
JWE . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.3. Key Encryption with RSAES-PKCS1-V1_5 . . . . . . . . . . . 15
4.4. Key Encryption with RSAES OAEP . . . . . . . . . . . . . . 15
4.5. Key Encryption with AES Key Wrap . . . . . . . . . . . . . 15
4.6. Direct Encryption with a Shared Symmetric Key . . . . . . 15
4.7. Key Agreement with Elliptic Curve Diffie-Hellman
Ephemeral Static (ECDH-ES) . . . . . . . . . . . . . . . . 15
4.7.1. Key Derivation for "ECDH-ES" . . . . . . . . . . . . . 16
4.8. Composite Plaintext Encryption Algorithms
"A128CBC+HS256" and "A256CBC+HS512" . . . . . . . . . . . 17
4.8.1. Key Derivation for "A128CBC+HS256" and
"A256CBC+HS512" . . . . . . . . . . . . . . . . . . . 17
4.8.2. Encryption Calculation for "A128CBC+HS256" and
"A256CBC+HS512" . . . . . . . . . . . . . . . . . . . 18
4.8.3. Integrity Calculation for "A128CBC+HS256" and
"A256CBC+HS512" . . . . . . . . . . . . . . . . . . . 18
4.9. Plaintext Encryption with AES GCM . . . . . . . . . . . . 19
4.10. Additional Encryption Algorithms and Parameters . . . . . 19
5. Cryptographic Algorithms for JWK . . . . . . . . . . . . . . . 20
5.1. "alg" (Algorithm Family) Parameter Values for JWK . . . . 20
5.2. JWK Parameters for Elliptic Curve Keys . . . . . . . . . . 21
5.2.1. "crv" (Curve) Parameter . . . . . . . . . . . . . . . 21
5.2.2. "x" (X Coordinate) Parameter . . . . . . . . . . . . . 21
5.2.3. "y" (Y Coordinate) Parameter . . . . . . . . . . . . . 21
5.3. JWK Parameters for RSA Keys . . . . . . . . . . . . . . . 22
5.3.1. "mod" (Modulus) Parameter . . . . . . . . . . . . . . 22
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5.3.2. "xpo" (Exponent) Parameter . . . . . . . . . . . . . . 22
5.4. Additional Key Algorithm Families and Parameters . . . . . 22
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
6.1. JSON Web Signature and Encryption Algorithms Registry . . 23
6.1.1. Registration Template . . . . . . . . . . . . . . . . 23
6.1.2. Initial Registry Contents . . . . . . . . . . . . . . 24
6.2. JSON Web Key Algorithm Families Registry . . . . . . . . . 27
6.2.1. Registration Template . . . . . . . . . . . . . . . . 27
6.2.2. Initial Registry Contents . . . . . . . . . . . . . . 28
6.3. JSON Web Key Parameters Registration . . . . . . . . . . . 28
6.3.1. Registry Contents . . . . . . . . . . . . . . . . . . 28
7. Security Considerations . . . . . . . . . . . . . . . . . . . 29
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30
8.1. Normative References . . . . . . . . . . . . . . . . . . . 30
8.2. Informative References . . . . . . . . . . . . . . . . . . 31
Appendix A. Digital Signature/MAC Algorithm Identifier
Cross-Reference . . . . . . . . . . . . . . . . . . . 32
Appendix B. Encryption Algorithm Identifier Cross-Reference . . . 34
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 36
Appendix D. Open Issues . . . . . . . . . . . . . . . . . . . . . 37
Appendix E. Document History . . . . . . . . . . . . . . . . . . 37
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 40
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1. Introduction
The JSON Web Algorithms (JWA) specification enumerates cryptographic
algorithms and identifiers to be used with the JSON Web Signature
(JWS) [JWS], JSON Web Encryption (JWE) [JWE], and JSON Web Key (JWK)
[JWK] specifications. All these specifications utilize JavaScript
Object Notation (JSON) [RFC4627] based data structures. This
specification also describes the semantics and operations that are
specific to these algorithms and algorithm families.
Enumerating the algorithms and identifiers for them in this
specification, rather than in the JWS, JWE, and JWK specifications,
is intended to allow them to remain unchanged in the face of changes
in the set of required, recommended, optional, and deprecated
algorithms over time.
1.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in Key words for use in
RFCs to Indicate Requirement Levels [RFC2119].
2. Terminology
2.1. Terms Incorporated from the JWS Specification
These terms defined by the JSON Web Signature (JWS) [JWS]
specification are incorporated into this specification:
JSON Web Signature (JWS) A data structure cryptographically securing
a JWS Header and a JWS Payload with a JWS Signature value.
JWS Header A string representing a JavaScript Object Notation (JSON)
[RFC4627] object that describes the digital signature or MAC
operation applied to create the JWS Signature value.
JWS Payload The bytes to be secured -- a.k.a., the message. The
payload can contain an arbitrary sequence of bytes.
JWS Signature A byte array containing the cryptographic material
that secures the contents of the JWS Header and the JWS Payload.
Base64url Encoding The URL- and filename-safe Base64 encoding
described in RFC 4648 [RFC4648], Section 5, with the (non URL-
safe) '=' padding characters omitted, as permitted by Section 3.2.
(See Appendix C of [JWS] for notes on implementing base64url
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encoding without padding.)
Encoded JWS Header Base64url encoding of the bytes of the UTF-8
[RFC3629] representation of the JWS Header.
Encoded JWS Payload Base64url encoding of the JWS Payload.
Encoded JWS Signature Base64url encoding of the JWS Signature.
JWS Secured Input The concatenation of the Encoded JWS Header, a
period ('.') character, and the Encoded JWS Payload.
Collision Resistant Namespace A namespace that allows names to be
allocated in a manner such that they are highly unlikely to
collide with other names. For instance, collision resistance can
be achieved through administrative delegation of portions of the
namespace or through use of collision-resistant name allocation
functions. Examples of Collision Resistant Namespaces include:
Domain Names, Object Identifiers (OIDs) as defined in the ITU-T
X.660 and X.670 Recommendation series, and Universally Unique
IDentifiers (UUIDs) [RFC4122]. When using an administratively
delegated namespace, the definer of a name needs to take
reasonable precautions to ensure they are in control of the
portion of the namespace they use to define the name.
2.2. Terms Incorporated from the JWE Specification
These terms defined by the JSON Web Encryption (JWE) [JWE]
specification are incorporated into this specification:
JSON Web Encryption (JWE) A data structure representing an encrypted
version of a Plaintext. The structure consists of four parts: the
JWE Header, the JWE Encrypted Key, the JWE Ciphertext, and the JWE
Integrity Value.
Plaintext The bytes to be encrypted -- a.k.a., the message. The
plaintext can contain an arbitrary sequence of bytes.
Ciphertext The encrypted version of the Plaintext.
Content Encryption Key (CEK) A symmetric key used to encrypt the
Plaintext for the recipient to produce the Ciphertext.
Content Integrity Key (CIK) A key used with a MAC function to ensure
the integrity of the Ciphertext and the parameters used to create
it.
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Content Master Key (CMK) A key from which the CEK and CIK are
derived. When key wrapping or key encryption are employed, the
CMK is randomly generated and encrypted to the recipient as the
JWE Encrypted Key. When key agreement is employed, the CMK is the
result of the key agreement algorithm.
JWE Header A string representing a JSON object that describes the
encryption operations applied to create the JWE Encrypted Key, the
JWE Ciphertext, and the JWE Integrity Value.
JWE Encrypted Key When key wrapping or key encryption are employed,
the Content Master Key (CMK) is encrypted with the intended
recipient's key and the resulting encrypted content is recorded as
a byte array, which is referred to as the JWE Encrypted Key.
Otherwise, when key agreement is employed, the JWE Encrypted Key
is the empty byte array.
JWE Ciphertext A byte array containing the Ciphertext.
JWE Integrity Value A byte array containing a MAC value that ensures
the integrity of the Ciphertext and the parameters used to create
it.
Encoded JWE Header Base64url encoding of the bytes of the UTF-8
[RFC3629] representation of the JWE Header.
Encoded JWE Encrypted Key Base64url encoding of the JWE Encrypted
Key.
Encoded JWE Ciphertext Base64url encoding of the JWE Ciphertext.
Encoded JWE Integrity Value Base64url encoding of the JWE Integrity
Value.
AEAD Algorithm An Authenticated Encryption with Associated Data
(AEAD) [RFC5116] encryption algorithm is one that provides an
integrated content integrity check. AES Galois/Counter Mode (GCM)
is one such algorithm.
2.3. Terms Incorporated from the JWK Specification
These terms defined by the JSON Web Key (JWK) [JWK] specification are
incorporated into this specification:
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JSON Web Key (JWK) A JSON data structure that represents a public
key.
JSON Web Key Set (JWK Set) A JSON object that contains an array of
JWKs as a member.
2.4. Defined Terms
These terms are defined for use by this specification:
Header Parameter Name The name of a member of the JSON object
representing a JWS Header or JWE Header.
Header Parameter Value The value of a member of the JSON object
representing a JWS Header or JWE Header.
3. Cryptographic Algorithms for JWS
JWS uses cryptographic algorithms to digitally sign or create a
Message Authentication Codes (MAC) of the contents of the JWS Header
and the JWS Payload. The use of the following algorithms for
producing JWSs is defined in this section.
3.1. "alg" (Algorithm) Header Parameter Values for JWS
The table below is the set of "alg" (algorithm) header parameter
values defined by this specification for use with JWS, each of which
is explained in more detail in the following sections:
+--------------+--------------------------------+-------------------+
| alg | Digital Signature or MAC | Implementation |
| Parameter | Algorithm | Requirements |
| Value | | |
+--------------+--------------------------------+-------------------+
| HS256 | HMAC using SHA-256 hash | REQUIRED |
| | algorithm | |
| HS384 | HMAC using SHA-384 hash | OPTIONAL |
| | algorithm | |
| HS512 | HMAC using SHA-512 hash | OPTIONAL |
| | algorithm | |
| RS256 | RSASSA using SHA-256 hash | RECOMMENDED |
| | algorithm | |
| RS384 | RSASSA using SHA-384 hash | OPTIONAL |
| | algorithm | |
| RS512 | RSASSA using SHA-512 hash | OPTIONAL |
| | algorithm | |
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| ES256 | ECDSA using P-256 curve and | RECOMMENDED+ |
| | SHA-256 hash algorithm | |
| ES384 | ECDSA using P-384 curve and | OPTIONAL |
| | SHA-384 hash algorithm | |
| ES512 | ECDSA using P-521 curve and | OPTIONAL |
| | SHA-512 hash algorithm | |
| none | No digital signature or MAC | REQUIRED |
| | value included | |
+--------------+--------------------------------+-------------------+
All the names are short because a core goal of JWS is for the
representations to be compact. However, there is no a priori length
restriction on "alg" values.
The use of "+" in the Implementation Requirements indicates that the
requirement strength is likely to be increased in a future version of
the specification.
See Appendix A for a table cross-referencing the digital signature
and MAC "alg" (algorithm) values used in this specification with the
equivalent identifiers used by other standards and software packages.
3.2. MAC with HMAC SHA-256, HMAC SHA-384, or HMAC SHA-512
Hash-based Message Authentication Codes (HMACs) enable one to use a
secret plus a cryptographic hash function to generate a Message
Authentication Code (MAC). This can be used to demonstrate that the
MAC matches the hashed content, in this case the JWS Secured Input,
which therefore demonstrates that whoever generated the MAC was in
possession of the secret. The means of exchanging the shared key is
outside the scope of this specification.
The algorithm for implementing and validating HMACs is provided in
RFC 2104 [RFC2104]. This section defines the use of the HMAC SHA-
256, HMAC SHA-384, and HMAC SHA-512 functions [SHS]. The "alg"
(algorithm) header parameter values "HS256", "HS384", and "HS512" are
used in the JWS Header to indicate that the Encoded JWS Signature
contains a base64url encoded HMAC value using the respective hash
function.
A key of the same size as the hash output (for instance, 256 bits for
"HS256") or larger MUST be used with this algorithm.
The HMAC SHA-256 MAC is generated per RFC 2104, using SHA-256 as the
hash algorithm "H", using the bytes of the ASCII [USASCII]
representation of the JWS Secured Input as the "text" value, and
using the shared key. The HMAC output value is the JWS Signature.
The JWS signature is base64url encoded to produce the Encoded JWS
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Signature.
The HMAC SHA-256 MAC for a JWS is validated by computing an HMAC
value per RFC 2104, using SHA-256 as the hash algorithm "H", using
the bytes of the ASCII representation of the received JWS Secured
input as the "text" value, and using the shared key. This computed
HMAC value is then compared to the result of base64url decoding the
received Encoded JWS signature. Alternatively, the computed HMAC
value can be base64url encoded and compared to the received Encoded
JWS Signature, as this comparison produces the same result as
comparing the unencoded values. In either case, if the values match,
the HMAC has been validated. If the validation fails, the JWS MUST
be rejected.
Securing content with the HMAC SHA-384 and HMAC SHA-512 algorithms is
performed identically to the procedure for HMAC SHA-256 - just using
the corresponding hash algorithm with correspondingly larger minimum
key sizes and result values: 384 bits each for HMAC SHA-384 and 512
bits each for HMAC SHA-512.
An example using this algorithm is shown in Appendix A.1 of [JWS].
3.3. Digital Signature with RSA SHA-256, RSA SHA-384, or RSA SHA-512
This section defines the use of the RSASSA-PKCS1-V1_5 digital
signature algorithm as defined in Section 8.2 of RFC 3447 [RFC3447],
(commonly known as PKCS #1), using SHA-256, SHA-384, or SHA-512 [SHS]
as the hash functions. The "alg" (algorithm) header parameter values
"RS256", "RS384", and "RS512" are used in the JWS Header to indicate
that the Encoded JWS Signature contains a base64url encoded RSA
digital signature using the respective hash function.
A key of size 2048 bits or larger MUST be used with these algorithms.
The RSA SHA-256 digital signature is generated as follows:
1. Generate a digital signature of the bytes of the ASCII
representation of the JWS Secured Input using RSASSA-PKCS1-V1_5-
SIGN and the SHA-256 hash function with the desired private key.
The output will be a byte array.
2. Base64url encode the resulting byte array.
The output is the Encoded JWS Signature for that JWS.
The RSA SHA-256 digital signature for a JWS is validated as follows:
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1. Take the Encoded JWS Signature and base64url decode it into a
byte array. If decoding fails, the JWS MUST be rejected.
2. Submit the bytes of the ASCII representation of the JWS Secured
Input and the public key corresponding to the private key used by
the signer to the RSASSA-PKCS1-V1_5-VERIFY algorithm using SHA-
256 as the hash function.
3. If the validation fails, the JWS MUST be rejected.
Signing with the RSA SHA-384 and RSA SHA-512 algorithms is performed
identically to the procedure for RSA SHA-256 - just using the
corresponding hash algorithm with correspondingly larger result
values: 384 bits for RSA SHA-384 and 512 bits for RSA SHA-512.
An example using this algorithm is shown in Appendix A.2 of [JWS].
3.4. Digital Signature with ECDSA P-256 SHA-256, ECDSA P-384 SHA-384,
or ECDSA P-521 SHA-512
The Elliptic Curve Digital Signature Algorithm (ECDSA) [DSS] provides
for the use of Elliptic Curve cryptography, which is able to provide
equivalent security to RSA cryptography but using shorter key sizes
and with greater processing speed. This means that ECDSA digital
signatures will be substantially smaller in terms of length than
equivalently strong RSA digital signatures.
This specification defines the use of ECDSA with the P-256 curve and
the SHA-256 cryptographic hash function, ECDSA with the P-384 curve
and the SHA-384 hash function, and ECDSA with the P-521 curve and the
SHA-512 hash function. The P-256, P-384, and P-521 curves are
defined in [DSS]. The "alg" (algorithm) header parameter values
"ES256", "ES384", and "ES512" are used in the JWS Header to indicate
that the Encoded JWS Signature contains a base64url encoded ECDSA
P-256 SHA-256, ECDSA P-384 SHA-384, or ECDSA P-521 SHA-512 digital
signature, respectively.
The ECDSA P-256 SHA-256 digital signature is generated as follows:
1. Generate a digital signature of the bytes of the ASCII
representation of the JWS Secured Input using ECDSA P-256 SHA-256
with the desired private key. The output will be the pair (R,
S), where R and S are 256 bit unsigned integers.
2. Turn R and S into byte arrays in big endian order, with each
array being be 32 bytes long. The array representations MUST not
be shortened to omit any leading zero bytes contained in the
values.
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3. Concatenate the two byte arrays in the order R and then S. (Note
that many ECDSA implementations will directly produce this
concatenation as their output.)
4. Base64url encode the resulting 64 byte array.
The output is the Encoded JWS Signature for the JWS.
The ECDSA P-256 SHA-256 digital signature for a JWS is validated as
follows:
1. Take the Encoded JWS Signature and base64url decode it into a
byte array. If decoding fails, the JWS MUST be rejected.
2. The output of the base64url decoding MUST be a 64 byte array. If
decoding does not result in a 64 byte array, the JWS MUST be
rejected.
3. Split the 64 byte array into two 32 byte arrays. The first array
will be R and the second S (with both being in big endian byte
order).
4. Submit the bytes of the ASCII representation of the JWS Secured
Input R, S and the public key (x, y) to the ECDSA P-256 SHA-256
validator.
5. If the validation fails, the JWS MUST be rejected.
Note that ECDSA digital signature contains a value referred to as K,
which is a random number generated for each digital signature
instance. This means that two ECDSA digital signatures using exactly
the same input parameters will output different signature values
because their K values will be different. A consequence of this is
that one cannot validate an ECDSA signature by recomputing the
signature and comparing the results.
Signing with the ECDSA P-384 SHA-384 and ECDSA P-521 SHA-512
algorithms is performed identically to the procedure for ECDSA P-256
SHA-256 - just using the corresponding hash algorithm with
correspondingly larger result values. For ECDSA P-384 SHA-384, R and
S will be 384 bits each, resulting in a 96 byte array. For ECDSA
P-521 SHA-512, R and S will be 521 bits each, resulting in a 132 byte
array.
Examples using these algorithms are shown in Appendices A.3 and A.4
of [JWS].
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3.5. Using the Algorithm "none"
JWSs MAY also be created that do not provide integrity protection.
Such a JWS is called a "Plaintext JWS". Plaintext JWSs MUST use the
"alg" value "none", and are formatted identically to other JWSs, but
with an empty JWS Signature value.
3.6. Additional Digital Signature/MAC Algorithms and Parameters
Additional algorithms MAY be used to protect JWSs with corresponding
"alg" (algorithm) header parameter values being defined to refer to
them. New "alg" header parameter values SHOULD either be registered
in the IANA JSON Web Signature and Encryption Algorithms registry
Section 6.1 or be a URI that contains a Collision Resistant
Namespace. In particular, it is permissible to use the algorithm
identifiers defined in XML DSIG [RFC3275], XML DSIG 2.0
[W3C.CR-xmldsig-core2-20120124], and related specifications as "alg"
values.
As indicated by the common registry, JWSs and JWEs share a common
"alg" value space. The values used by the two specifications MUST be
distinct, as the "alg" value MAY be used to determine whether the
object is a JWS or JWE.
Likewise, additional reserved header parameter names MAY be defined
via the IANA JSON Web Signature and Encryption Header Parameters
registry [JWS]. As indicated by the common registry, JWSs and JWEs
share a common header parameter space; when a parameter is used by
both specifications, its usage must be compatible between the
specifications.
4. Cryptographic Algorithms for JWE
JWE uses cryptographic algorithms to encrypt the Content Master Key
(CMK) and the Plaintext. This section specifies a set of specific
algorithms for these purposes.
4.1. "alg" (Algorithm) Header Parameter Values for JWE
The table below is the set of "alg" (algorithm) header parameter
values that are defined by this specification for use with JWE.
These algorithms are used to encrypt the CMK, producing the JWE
Encrypted Key, or to use key agreement to agree upon the CMK.
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+----------------+---------------------------------+----------------+
| alg Parameter | Key Encryption or Agreement | Implementation |
| Value | Algorithm | Requirements |
+----------------+---------------------------------+----------------+
| RSA1_5 | RSAES-PKCS1-V1_5 [RFC3447] | REQUIRED |
| RSA-OAEP | RSAES using Optimal Asymmetric | OPTIONAL |
| | Encryption Padding (OAEP) | |
| | [RFC3447], with the default | |
| | parameters specified by RFC | |
| | 3447 in Section A.2.1 | |
| A128KW | Advanced Encryption Standard | RECOMMENDED |
| | (AES) Key Wrap Algorithm | |
| | [RFC3394] using 128 bit keys | |
| A256KW | AES Key Wrap Algorithm using | RECOMMENDED |
| | 256 bit keys | |
| dir | Direct use of a shared | RECOMMENDED |
| | symmetric key as the Content | |
| | Master Key (CMK) for the block | |
| | encryption step (rather than | |
| | using the symmetric key to wrap | |
| | the CMK) | |
| ECDH-ES | Elliptic Curve Diffie-Hellman | RECOMMENDED+ |
| | Ephemeral Static [RFC6090] key | |
| | agreement using the Concat KDF, | |
| | as defined in Section 5.8.1 of | |
| | [NIST.800-56A], with the | |
| | agreed-upon key being used | |
| | directly as the Content Master | |
| | Key (CMK) (rather than being | |
| | used to wrap the CMK), as | |
| | specified in Section 4.7 | |
| ECDH-ES+A128KW | Elliptic Curve Diffie-Hellman | RECOMMENDED |
| | Ephemeral Static key agreement | |
| | per "ECDH-ES" and Section 4.7, | |
| | but where the agreed-upon key | |
| | is used to wrap the Content | |
| | Master Key (CMK) with the | |
| | "A128KW" function (rather than | |
| | being used directly as the CMK) | |
| ECDH-ES+A256KW | Elliptic Curve Diffie-Hellman | RECOMMENDED |
| | Ephemeral Static key agreement | |
| | per "ECDH-ES" and Section 4.7, | |
| | but where the agreed-upon key | |
| | is used to wrap the Content | |
| | Master Key (CMK) with the | |
| | "A256KW" function (rather than | |
| | being used directly as the CMK) | |
+----------------+---------------------------------+----------------+
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The use of "+" in the Implementation Requirements indicates that the
requirement strength is likely to be increased in a future version of
the specification.
4.2. "enc" (Encryption Method) Header Parameter Values for JWE
The table below is the set of "enc" (encryption method) header
parameter values that are defined by this specification for use with
JWE. These algorithms are used to encrypt the Plaintext, which
produces the Ciphertext.
+---------------+----------------------------------+----------------+
| enc Parameter | Block Encryption Algorithm | Implementation |
| Value | | Requirements |
+---------------+----------------------------------+----------------+
| A128CBC+HS256 | Composite AEAD algorithm using | REQUIRED |
| | Advanced Encryption Standard | |
| | (AES) in Cipher Block Chaining | |
| | (CBC) mode with PKCS #5 padding | |
| | [AES] [NIST.800-38A] with an | |
| | integrity calculation using HMAC | |
| | SHA-256, using a 256 bit CMK | |
| | (and 128 bit CEK) as specified | |
| | in Section 4.8 | |
| A256CBC+HS512 | Composite AEAD algorithm using | REQUIRED |
| | AES in CBC mode with PKCS #5 | |
| | padding with an integrity | |
| | calculation using HMAC SHA-512, | |
| | using a 512 bit CMK (and 256 bit | |
| | CEK) as specified in Section 4.8 | |
| A128GCM | AES in Galois/Counter Mode (GCM) | RECOMMENDED |
| | [AES] [NIST.800-38D] using 128 | |
| | bit keys | |
| A256GCM | AES GCM using 256 bit keys | RECOMMENDED |
+---------------+----------------------------------+----------------+
All the names are short because a core goal of JWE is for the
representations to be compact. However, there is no a priori length
restriction on "alg" values.
See Appendix B for a table cross-referencing the encryption "alg"
(algorithm) and "enc" (encryption method) values used in this
specification with the equivalent identifiers used by other standards
and software packages.
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4.3. Key Encryption with RSAES-PKCS1-V1_5
This section defines the specifics of encrypting a JWE CMK with
RSAES-PKCS1-V1_5 [RFC3447]. The "alg" header parameter value
"RSA1_5" is used in this case.
A key of size 2048 bits or larger MUST be used with this algorithm.
An example using this algorithm is shown in Appendix A.2 of [JWE].
4.4. Key Encryption with RSAES OAEP
This section defines the specifics of encrypting a JWE CMK with RSAES
using Optimal Asymmetric Encryption Padding (OAEP) [RFC3447], with
the default parameters specified by RFC 3447 in Section A.2.1. The
"alg" header parameter value "RSA-OAEP" is used in this case.
A key of size 2048 bits or larger MUST be used with this algorithm.
An example using this algorithm is shown in Appendix A.1 of [JWE].
4.5. Key Encryption with AES Key Wrap
This section defines the specifics of encrypting a JWE CMK with the
Advanced Encryption Standard (AES) Key Wrap Algorithm [RFC3394] using
128 or 256 bit keys. The "alg" header parameter values "A128KW" or
"A256KW" are used in this case.
An example using this algorithm is shown in Appendix A.3 of [JWE].
4.6. Direct Encryption with a Shared Symmetric Key
This section defines the specifics of directly performing symmetric
key encryption without performing a key wrapping step. In this case,
the shared symmetric key is used directly as the Content Master Key
(CMK) value for the "enc" algorithm. An empty byte array is used as
the JWE Encrypted Key value. The "alg" header parameter value "dir"
is used in this case.
4.7. Key Agreement with Elliptic Curve Diffie-Hellman Ephemeral Static
(ECDH-ES)
This section defines the specifics of key agreement with Elliptic
Curve Diffie-Hellman Ephemeral Static [RFC6090], and using the Concat
KDF, as defined in Section 5.8.1 of [NIST.800-56A]. The key
agreement result can be used in one of two ways: (1) directly as the
Content Master Key (CMK) for the "enc" algorithm, or (2) as a
symmetric key used to wrap the CMK with either the "A128KW" or
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"A256KW" algorithms. The "alg" header parameter values "ECDH-ES",
"ECDH-ES+A128KW", and "ECDH-ES+A256KW" are respectively used in this
case.
In the direct case, the output of the Concat KDF MUST be a key of the
same length as that used by the "enc" algorithm; in this case, the
empty byte array is used as the JWE Encrypted Key value. In the key
wrap case, the output of the Concat KDF MUST be a key of the length
needed for the specified key wrap algorithm, either 128 or 256 bits
respectively.
A new "epk" (ephemeral public key) value MUST be generated for each
key agreement transaction.
4.7.1. Key Derivation for "ECDH-ES"
The key derivation process derives the agreed upon key from the
shared secret Z established through the ECDH algorithm, per Section
6.2.2.2 of [NIST.800-56A].
Key derivation is performed using the Concat KDF, as defined in
Section 5.8.1 of [NIST.800-56A], where the Digest Method is SHA-256.
The Concat KDF parameters are set as follows:
Z This is set to the representation of the shared secret Z as a byte
array.
keydatalen This is set to the number of bits in the desired output
key. For "ECDH-ES", this is length of the key used by the "enc"
algorithm. For "ECDH-ES+A128KW", and "ECDH-ES+A256KW", this is
128 and 256, respectively.
AlgorithmID This is set to the concatenation of keydatalen
represented as a 32 bit big endian integer and the bytes of the
UTF-8 representation of the "alg" header parameter value.
PartyUInfo If an "apu" (agreement PartyUInfo) header parameter is
present, this is set to the result of base64url decoding the "apu"
value; otherwise, it is set to the empty byte string.
PartyVInfo If an "apv" (agreement PartyVInfo) header parameter is
present, this is set to the result of base64url decoding the "apv"
value; otherwise, it is set to the empty byte string.
SuppPubInfo This is set to the empty byte string.
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SuppPrivInfo This is set to the empty byte string.
For all three "alg" values, the digest function used is SHA-256.
4.8. Composite Plaintext Encryption Algorithms "A128CBC+HS256" and
"A256CBC+HS512"
This section defines two composite "enc" algorithms that perform
plaintext encryption using non-AEAD algorithms and add an integrity
check calculation, so that the resulting composite algorithms are
AEAD. These composite algorithms derive a Content Encryption Key
(CEK) and a Content Integrity Key (CIK) from a Content Master Key,
per Section 4.8.1. They perform block encryption with AES CBC, per
Section 4.8.2. Finally, they add an integrity check using HMAC SHA-2
algorithms of matching strength, per Section 4.8.3.
A 256 bit Content Master Key (CMK) value is used with the
"A128CBC+HS256" algorithm. A 512 bit Content Master Key (CMK) value
is used with the "A256CBC+HS512" algorithm.
An example using this algorithm is shown in Appendix A.2 of [JWE].
4.8.1. Key Derivation for "A128CBC+HS256" and "A256CBC+HS512"
The key derivation process derives CEK and CIK values from the CMK.
This section defines the specifics of deriving keys for the "enc"
algorithms "A128CBC+HS256" and "A256CBC+HS512".
Key derivation is performed using the Concat KDF, as defined in
Section 5.8.1 of [NIST.800-56A], where the Digest Method is SHA-256
or SHA-512, respectively. The Concat KDF parameters are set as
follows:
Z This is set to the Content Master Key (CMK).
keydatalen This is set to the number of bits in the desired output
key.
AlgorithmID This is set to the concatenation of keydatalen
represented as a 32 bit big endian integer and the bytes of the
UTF-8 representation of the "enc" header parameter value.
PartyUInfo If an "epu" (encryption PartyUInfo) header parameter is
present, this is set to the result of base64url decoding the "epu"
value; otherwise, it is set to the empty byte string.
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PartyVInfo If an "epv" (encryption PartyVInfo) header parameter is
present, this is set to the result of base64url decoding the "epv"
value; otherwise, it is set to the empty byte string.
SuppPubInfo This is set to the bytes of one of the ASCII strings
"Encryption" ([69, 110, 99, 114, 121, 112, 116, 105, 111, 110]) or
"Integrity" ([73, 110, 116, 101, 103, 114, 105, 116, 121])
respectively, depending upon whether the CEK or CIK is being
generated.
SuppPrivInfo This is set to the empty byte string.
To compute the CEK from the CMK, the ASCII label "Encryption" is used
for the SuppPubInfo value. For "A128CBC+HS256", the keydatalen is
128 and the digest function used is SHA-256. For "A256CBC+HS512",
the keydatalen is 256 and the digest function used is SHA-512.
To compute the CIK from the CMK, the ASCII label "Integrity" is used
for the SuppPubInfo value. For "A128CBC+HS256", the keydatalen is
256 and the digest function used is SHA-256. For "A256CBC+HS512",
the keydatalen is 512 and the digest function used is SHA-512.
Example derivation computations are shown in Appendices A.4 and A.5
of [JWE].
4.8.2. Encryption Calculation for "A128CBC+HS256" and "A256CBC+HS512"
This section defines the specifics of encrypting the JWE Plaintext
with Advanced Encryption Standard (AES) in Cipher Block Chaining
(CBC) mode with PKCS #5 padding [AES] [NIST.800-38A] using 128 or 256
bit keys. The "enc" header parameter values "A128CBC+HS256" or
"A256CBC+HS512" are respectively used in this case.
The CEK is used as the encryption key.
Use of an initialization vector of size 128 bits is REQUIRED with
these algorithms.
4.8.3. Integrity Calculation for "A128CBC+HS256" and "A256CBC+HS512"
This section defines the specifics of computing the JWE Integrity
Value for the "enc" algorithms "A128CBC+HS256" and "A256CBC+HS512".
This value is computed as a MAC of the JWE parameters to be secured.
The MAC input value is the bytes of the ASCII representation of the
concatenation of the Encoded JWE Header, a period ('.') character,
the Encoded JWE Encrypted Key, a second period character ('.'), the
Encoded JWE Initialization Vector, a third period ('.') character,
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and the Encoded JWE Ciphertext.
The CIK is used as the MAC key.
For "A128CBC+HS256", HMAC SHA-256 is used as the MAC algorithm. For
"A256CBC+HS512", HMAC SHA-512 is used as the MAC algorithm.
The resulting MAC value is used as the JWE Integrity Value. The same
integrity calculation is performed during decryption. During
decryption, the computed integrity value must match the received JWE
Integrity Value.
4.9. Plaintext Encryption with AES GCM
This section defines the specifics of encrypting the JWE Plaintext
with Advanced Encryption Standard (AES) in Galois/Counter Mode (GCM)
[AES] [NIST.800-38D] using 128 or 256 bit keys. The "enc" header
parameter values "A128GCM" or "A256GCM" are used in this case.
The CMK is used as the encryption key.
Use of an initialization vector of size 96 bits is REQUIRED with this
algorithm.
The "additional authenticated data" parameter is used to secure the
header and key values. The "additional authenticated data" value
used is the bytes of the ASCII representation of the concatenation of
the Encoded JWE Header, a period ('.') character, the Encoded JWE
Encrypted Key, a second period character ('.'), and the Encoded JWE
Initialization Vector. This same "additional authenticated data"
value is used when decrypting as well.
The requested size of the "authentication tag" output MUST be 128
bits, regardless of the key size.
As GCM is an AEAD algorithm, the JWE Integrity Value is set to be the
"authentication tag" value produced by the encryption. During
decryption, the received JWE Integrity Value is used as the
"authentication tag" value.
Examples using this algorithm are shown in Appendices A.1 and A.3 of
[JWE].
4.10. Additional Encryption Algorithms and Parameters
Additional algorithms MAY be used to protect JWEs with corresponding
"alg" (algorithm) and "enc" (encryption method) header parameter
values being defined to refer to them. New "alg" and "enc" header
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parameter values SHOULD either be registered in the IANA JSON Web
Signature and Encryption Algorithms registry Section 6.1 or be a URI
that contains a Collision Resistant Namespace. In particular, it is
permissible to use the algorithm identifiers defined in XML
Encryption [W3C.REC-xmlenc-core-20021210], XML Encryption 1.1
[W3C.CR-xmlenc-core1-20120313], and related specifications as "alg"
and "enc" values.
As indicated by the common registry, JWSs and JWEs share a common
"alg" value space. The values used by the two specifications MUST be
distinct, as the "alg" value MAY be used to determine whether the
object is a JWS or JWE.
Likewise, additional reserved header parameter names MAY be defined
via the IANA JSON Web Signature and Encryption Header Parameters
registry [JWS]. As indicated by the common registry, JWSs and JWEs
share a common header parameter space; when a parameter is used by
both specifications, its usage must be compatible between the
specifications.
5. Cryptographic Algorithms for JWK
A JSON Web Key (JWK) [JWK] is a JavaScript Object Notation (JSON)
[RFC4627] data structure that represents a public key. A JSON Web
Key Set (JWK Set) is a JSON data structure for representing a set of
JWKs. This section specifies a set of algorithm families to be used
for those public keys and the algorithm family specific parameters
for representing those keys.
5.1. "alg" (Algorithm Family) Parameter Values for JWK
The table below is the set of "alg" (algorithm family) parameter
values that are defined by this specification for use in JWKs.
+-----------------+-------------------------+-----------------------+
| alg Parameter | Algorithm Family | Implementation |
| Value | | Requirements |
+-----------------+-------------------------+-----------------------+
| EC | Elliptic Curve [DSS] | RECOMMENDED+ |
| | key family | |
| RSA | RSA [RFC3447] key | REQUIRED |
| | family | |
+-----------------+-------------------------+-----------------------+
All the names are short because a core goal of JWK is for the
representations to be compact. However, there is no a priori length
restriction on "alg" values.
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The use of "+" in the Implementation Requirements indicates that the
requirement strength is likely to be increased in a future version of
the specification.
5.2. JWK Parameters for Elliptic Curve Keys
JWKs can represent Elliptic Curve [DSS] keys. In this case, the
"alg" member value MUST be "EC". Furthermore, these additional
members MUST be present:
5.2.1. "crv" (Curve) Parameter
The "crv" (curve) member identifies the cryptographic curve used with
the key. Curve values from [DSS] used by this specification are:
o "P-256"
o "P-384"
o "P-521"
Additional "crv" values MAY be used, provided they are understood by
implementations using that Elliptic Curve key. The "crv" value is a
case sensitive string.
5.2.2. "x" (X Coordinate) Parameter
The "x" (x coordinate) member contains the x coordinate for the
elliptic curve point. It is represented as the base64url encoding of
the coordinate's big endian representation as a byte array. The
array representation MUST not be shortened to omit any leading zero
bytes contained in the value. For instance, when representing 521
bit integers, the byte array to be base64url encoded MUST contain 66
bytes, including any leading zero bytes.
5.2.3. "y" (Y Coordinate) Parameter
The "y" (y coordinate) member contains the y coordinate for the
elliptic curve point. It is represented as the base64url encoding of
the coordinate's big endian representation as a byte array. The
array representation MUST not be shortened to omit any leading zero
bytes contained in the value. For instance, when representing 521
bit integers, the byte array to be base64url encoded MUST contain 66
bytes, including any leading zero bytes.
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5.3. JWK Parameters for RSA Keys
JWKs can represent RSA [RFC3447] keys. In this case, the "alg"
member value MUST be "RSA". Furthermore, these additional members
MUST be present:
5.3.1. "mod" (Modulus) Parameter
The "mod" (modulus) member contains the modulus value for the RSA
public key. It is represented as the base64url encoding of the
value's unsigned big endian representation as a byte array. The
array representation MUST not be shortened to omit any leading zero
bytes. For instance, when representing 2048 bit integers, the byte
array to be base64url encoded MUST contain 256 bytes, including any
leading zero bytes.
5.3.2. "xpo" (Exponent) Parameter
The "xpo" (exponent) member contains the exponent value for the RSA
public key. It is represented as the base64url encoding of the
value's unsigned big endian representation as a byte array. The
array representation MUST utilize the minimum number of bytes to
represent the value. For instance, when representing the value
65537, the byte array to be base64url encoded MUST consist of the
three bytes [1, 0, 1].
5.4. Additional Key Algorithm Families and Parameters
Public keys using additional algorithm families MAY be represented
using JWK data structures with corresponding "alg" (algorithm family)
parameter values being defined to refer to them. New "alg" parameter
values SHOULD either be registered in the IANA JSON Web Key Algorithm
Families registry Section 6.2 or be a URI that contains a Collision
Resistant Namespace.
Likewise, parameters for representing keys for additional algorithm
families or additional key properties SHOULD either be registered in
the IANA JSON Web Key Parameters registry [JWK] or be a URI that
contains a Collision Resistant Namespace.
6. IANA Considerations
The following registration procedure is used for all the registries
established by this specification.
Values are registered with a Specification Required [RFC5226] after a
two-week review period on the [TBD]@ietf.org mailing list, on the
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advice of one or more Designated Experts. However, to allow for the
allocation of values prior to publication, the Designated Expert(s)
may approve registration once they are satisfied that such a
specification will be published.
Registration requests must be sent to the [TBD]@ietf.org mailing list
for review and comment, with an appropriate subject (e.g., "Request
for access token type: example"). [[ Note to RFC-EDITOR: The name of
the mailing list should be determined in consultation with the IESG
and IANA. Suggested name: jose-reg-review. ]]
Within the review period, the Designated Expert(s) will either
approve or deny the registration request, communicating this decision
to the review list and IANA. Denials should include an explanation
and, if applicable, suggestions as to how to make the request
successful.
IANA must only accept registry updates from the Designated Expert(s)
and should direct all requests for registration to the review mailing
list.
6.1. JSON Web Signature and Encryption Algorithms Registry
This specification establishes the IANA JSON Web Signature and
Encryption Algorithms registry for values of the JWS and JWE "alg"
(algorithm) and "enc" (encryption method) header parameters. The
registry records the algorithm name, the algorithm usage locations
from the set "alg" and "enc", implementation requirements, and a
reference to the specification that defines it. The same algorithm
name may be registered multiple times, provided that the sets of
usage locations are disjoint. The implementation requirements of an
algorithm may be changed over time by the Designated Experts(s) as
the cryptographic landscape evolves, for instance, to change the
status of an algorithm to DEPRECATED, or to change the status of an
algorithm from OPTIONAL to RECOMMENDED or REQUIRED.
6.1.1. Registration Template
Algorithm Name:
The name requested (e.g., "example"). This name is case
sensitive. Names that match other registered names in a case
insensitive manner SHOULD NOT be accepted.
Algorithm Usage Location(s):
The algorithm usage, which must be one or more of the values "alg"
or "enc".
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Implementation Requirements:
The algorithm implementation requirements, which must be one the
words REQUIRED, RECOMMENDED, OPTIONAL, or DEPRECATED. Optionally,
the word may be followed by a "+" or "-". The use of "+"
indicates that the requirement strength is likely to be increased
in a future version of the specification. The use of "-"
indicates that the requirement strength is likely to be decreased
in a future version of the specification.
Change Controller:
For Standards Track RFCs, state "IETF". For others, give the name
of the responsible party. Other details (e.g., postal address,
email address, home page URI) may also be included.
Specification Document(s):
Reference to the document(s) that specify the parameter,
preferably including URI(s) that can be used to retrieve copies of
the document(s). An indication of the relevant sections may also
be included but is not required.
6.1.2. Initial Registry Contents
o Algorithm Name: "HS256"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: REQUIRED
o Change Controller: IETF
o Specification Document(s): Section 3.1 of [[ this document ]]
o Algorithm Name: "HS384"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: OPTIONAL
o Change Controller: IETF
o Specification Document(s): Section 3.1 of [[ this document ]]
o Algorithm Name: "HS512"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: OPTIONAL
o Change Controller: IETF
o Specification Document(s): Section 3.1 of [[ this document ]]
o Algorithm Name: "RS256"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: RECOMMENDED
o Change Controller: IETF
o Specification Document(s): Section 3.1 of [[ this document ]]
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o Algorithm Name: "RS384"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: OPTIONAL
o Change Controller: IETF
o Specification Document(s): Section 3.1 of [[ this document ]]
o Algorithm Name: "RS512"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: OPTIONAL
o Change Controller: IETF
o Specification Document(s): Section 3.1 of [[ this document ]]
o Algorithm Name: "ES256"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: RECOMMENDED+
o Change Controller: IETF
o Specification Document(s): Section 3.1 of [[ this document ]]
o Algorithm Name: "ES384"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: OPTIONAL
o Change Controller: IETF
o Specification Document(s): Section 3.1 of [[ this document ]]
o Algorithm Name: "ES512"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: OPTIONAL
o Change Controller: IETF
o Specification Document(s): Section 3.1 of [[ this document ]]
o Algorithm Name: "none"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: REQUIRED
o Change Controller: IETF
o Specification Document(s): Section 3.1 of [[ this document ]]
o Algorithm Name: "RSA1_5"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: REQUIRED
o Change Controller: IETF
o Specification Document(s): Section 4.1 of [[ this document ]]
o Algorithm Name: "RSA-OAEP"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: OPTIONAL
o Change Controller: IETF
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o Specification Document(s): Section 4.1 of [[ this document ]]
o Algorithm Name: "A128KW"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: RECOMMENDED
o Change Controller: IETF
o Specification Document(s): Section 4.1 of [[ this document ]]
o Algorithm Name: "A256KW"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: RECOMMENDED
o Change Controller: IETF
o Specification Document(s): Section 4.1 of [[ this document ]]
o Algorithm Name: "dir"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: RECOMMENDED
o Change Controller: IETF
o Specification Document(s): Section 4.1 of [[ this document ]]
o Algorithm Name: "ECDH-ES"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: RECOMMENDED+
o Change Controller: IETF
o Specification Document(s): Section 4.1 of [[ this document ]]
o Algorithm Name: "ECDH-ES+A128KW"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: RECOMMENDED
o Change Controller: IETF
o Specification Document(s): Section 4.1 of [[ this document ]]
o Algorithm Name: "ECDH-ES+A256KW"
o Algorithm Usage Location(s): "alg"
o Implementation Requirements: RECOMMENDED
o Change Controller: IETF
o Specification Document(s): Section 4.1 of [[ this document ]]
o Algorithm Name: "A128CBC+HS256"
o Algorithm Usage Location(s): "enc"
o Implementation Requirements: REQUIRED
o Change Controller: IETF
o Specification Document(s): Section 4.2 of [[ this document ]]
o Algorithm Name: "A256CBC+HS512"
o Algorithm Usage Location(s): "enc"
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o Implementation Requirements: REQUIRED
o Change Controller: IETF
o Specification Document(s): Section 4.2 of [[ this document ]]
o Algorithm Name: "A128GCM"
o Algorithm Usage Location(s): "enc"
o Implementation Requirements: RECOMMENDED
o Change Controller: IETF
o Specification Document(s): Section 4.2 of [[ this document ]]
o Algorithm Name: "A256GCM"
o Algorithm Usage Location(s): "enc"
o Implementation Requirements: RECOMMENDED
o Change Controller: IETF
o Specification Document(s): Section 4.2 of [[ this document ]]
6.2. JSON Web Key Algorithm Families Registry
This specification establishes the IANA JSON Web Key Algorithm
Families registry for values of the JWK "alg" (algorithm family)
parameter. The registry records the "alg" value and a reference to
the specification that defines it. This specification registers the
values defined in Section 5.1.
6.2.1. Registration Template
"alg" Parameter Value:
The name requested (e.g., "example"). This name is case
sensitive. Names that match other registered names in a case
insensitive manner SHOULD NOT be accepted.
Change Controller:
For Standards Track RFCs, state "IETF". For others, give the name
of the responsible party. Other details (e.g., postal address,
email address, home page URI) may also be included.
Implementation Requirements:
The algorithm implementation requirements, which must be one the
words REQUIRED, RECOMMENDED, OPTIONAL, or DEPRECATED. Optionally,
the word may be followed by a "+" or "-". The use of "+"
indicates that the requirement strength is likely to be increased
in a future version of the specification. The use of "-"
indicates that the requirement strength is likely to be decreased
in a future version of the specification.
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Specification Document(s):
Reference to the document(s) that specify the parameter,
preferably including URI(s) that can be used to retrieve copies of
the document(s). An indication of the relevant sections may also
be included but is not required.
6.2.2. Initial Registry Contents
o "alg" Parameter Value: "EC"
o Implementation Requirements: RECOMMENDED+
o Change Controller: IETF
o Specification Document(s): Section 5.1 of [[ this document ]]
o "alg" Parameter Value: "RSA"
o Implementation Requirements: REQUIRED
o Change Controller: IETF
o Specification Document(s): Section 5.1 of [[ this document ]]
6.3. JSON Web Key Parameters Registration
This specification registers the parameter names defined in Sections
5.2 and 5.3 in the IANA JSON Web Key Parameters registry [JWK].
6.3.1. Registry Contents
o Parameter Name: "crv"
o Change Controller: IETF
o Specification Document(s): Section 5.2.1 of [[ this document ]]
o Parameter Name: "x"
o Change Controller: IETF
o Specification Document(s): Section 5.2.2 of [[ this document ]]
o Parameter Name: "y"
o Change Controller: IETF
o Specification Document(s): Section 5.2.3 of [[ this document ]]
o Parameter Name: "mod"
o Change Controller: IETF
o Specification Document(s): Section 5.3.1 of [[ this document ]]
o Parameter Name: "xpo"
o Change Controller: IETF
o Specification Document(s): Section 5.3.2 of [[ this document ]]
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7. Security Considerations
All of the security issues faced by any cryptographic application
must be faced by a JWS/JWE/JWK agent. Among these issues are
protecting the user's private key, preventing various attacks, and
helping the user avoid mistakes such as inadvertently encrypting a
message for the wrong recipient. The entire list of security
considerations is beyond the scope of this document, but some
significant concerns are listed here.
The security considerations in [AES], [DSS], [JWE], [JWK], [JWS],
[NIST.800-38A], [NIST.800-38D], [NIST.800-56A], [RFC2104], [RFC3394],
[RFC3447], [RFC5116], [RFC6090], and [SHS] apply to this
specification.
Eventually the algorithms and/or key sizes currently described in
this specification will no longer be considered sufficiently secure
and will be removed. Therefore, implementers and deployments must be
prepared for this eventuality.
Algorithms of matching strength should be used together whenever
possible. For instance, when AES Key Wrap is used with a given key
size, using the same key size is recommended when AES GCM is also
used.
While Section 8 of RFC 3447 [RFC3447] explicitly calls for people not
to adopt RSASSA-PKCS1 for new applications and instead requests that
people transition to RSASSA-PSS, this specification does include
RSASSA-PKCS1, for interoperability reasons, because it commonly
implemented.
Keys used with RSAES-PKCS1-v1_5 must follow the constraints in
Section 7.2 of RFC 3447 [RFC3447]. In particular, keys with a low
public key exponent value must not be used.
Plaintext JWSs (JWSs that use the "alg" value "none") provide no
integrity protection. Thus, they must only be used in contexts where
the payload is secured by means other than a digital signature or MAC
value, or need not be secured.
Receiving agents that validate signatures and sending agents that
encrypt messages need to be cautious of cryptographic processing
usage when validating signatures and encrypting messages using keys
larger than those mandated in this specification. An attacker could
send certificates with keys that would result in excessive
cryptographic processing, for example, keys larger than those
mandated in this specification, which could swamp the processing
element. Agents that use such keys without first validating the
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certificate to a trust anchor are advised to have some sort of
cryptographic resource management system to prevent such attacks.
8. References
8.1. Normative References
[AES] National Institute of Standards and Technology (NIST),
"Advanced Encryption Standard (AES)", FIPS PUB 197,
November 2001.
[DSS] National Institute of Standards and Technology, "Digital
Signature Standard (DSS)", FIPS PUB 186-3, June 2009.
[JWE] Jones, M., Rescorla, E., and J. Hildebrand, "JSON Web
Encryption (JWE)", October 2012.
[JWK] Jones, M., "JSON Web Key (JWK)", October 2012.
[JWS] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", October 2012.
[NIST.800-38A]
National Institute of Standards and Technology (NIST),
"Recommendation for Block Cipher Modes of Operation",
NIST PUB 800-38A, December 2001.
[NIST.800-38D]
National Institute of Standards and Technology (NIST),
"Recommendation for Block Cipher Modes of Operation:
Galois/Counter Mode (GCM) and GMAC", NIST PUB 800-38D,
December 2001.
[NIST.800-56A]
National Institute of Standards and Technology (NIST),
"Recommendation for Pair-Wise Key Establishment Schemes
Using Discrete Logarithm Cryptography (Revised)", NIST PUB
800-56A, March 2007.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
February 1997.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3394] Schaad, J. and R. Housley, "Advanced Encryption Standard
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(AES) Key Wrap Algorithm", RFC 3394, September 2002.
[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications
Version 2.1", RFC 3447, February 2003.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC4627] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627, July 2006.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, January 2008.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
Curve Cryptography Algorithms", RFC 6090, February 2011.
[SHS] National Institute of Standards and Technology, "Secure
Hash Standard (SHS)", FIPS PUB 180-3, October 2008.
[USASCII] American National Standards Institute, "Coded Character
Set -- 7-bit American Standard Code for Information
Interchange", ANSI X3.4, 1986.
8.2. Informative References
[CanvasApp]
Facebook, "Canvas Applications", 2010.
[I-D.rescorla-jsms]
Rescorla, E. and J. Hildebrand, "JavaScript Message
Security Format", draft-rescorla-jsms-00 (work in
progress), March 2011.
[JCA] Oracle, "Java Cryptography Architecture", 2011.
[JSE] Bradley, J. and N. Sakimura (editor), "JSON Simple
Encryption", September 2010.
[JSS] Bradley, J. and N. Sakimura (editor), "JSON Simple Sign",
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September 2010.
[MagicSignatures]
Panzer (editor), J., Laurie, B., and D. Balfanz, "Magic
Signatures", January 2011.
[RFC3275] Eastlake, D., Reagle, J., and D. Solo, "(Extensible Markup
Language) XML-Signature Syntax and Processing", RFC 3275,
March 2002.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
July 2005.
[W3C.CR-xmldsig-core2-20120124]
Roessler, T., Yiu, K., Solo, D., Reagle, J., Datta, P.,
Eastlake, D., Hirsch, F., and S. Cantor, "XML Signature
Syntax and Processing Version 2.0", World Wide Web
Consortium CR CR-xmldsig-core2-20120124, January 2012,
<http://www.w3.org/TR/2012/CR-xmldsig-core2-20120124>.
[W3C.CR-xmlenc-core1-20120313]
Eastlake, D., Reagle, J., Hirsch, F., and T. Roessler,
"XML Encryption Syntax and Processing Version 1.1", World
Wide Web Consortium CR CR-xmlenc-core1-20120313,
March 2012,
<http://www.w3.org/TR/2012/CR-xmlenc-core1-20120313>.
[W3C.REC-xmlenc-core-20021210]
Eastlake, D. and J. Reagle, "XML Encryption Syntax and
Processing", World Wide Web Consortium Recommendation REC-
xmlenc-core-20021210, December 2002,
<http://www.w3.org/TR/2002/REC-xmlenc-core-20021210>.
Appendix A. Digital Signature/MAC Algorithm Identifier Cross-Reference
This appendix contains a table cross-referencing the digital
signature and MAC "alg" (algorithm) values used in this specification
with the equivalent identifiers used by other standards and software
packages. See XML DSIG [RFC3275], XML DSIG 2.0
[W3C.CR-xmldsig-core2-20120124], and Java Cryptography Architecture
[JCA] for more information about the names defined by those
documents.
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+-------+-----+----------------------------+----------+-------------+
| Algor | JWS | XML DSIG | JCA | OID |
| ithm | | | | |
+-------+-----+----------------------------+----------+-------------+
| HMAC | HS2 | http://www.w3.org/2001/04/ | HmacSHA2 | 1.2.840.113 |
| using | 56 | xmldsig-more#hmac-sha256 | 56 | 549.2.9 |
| SHA-2 | | | | |
| 56 | | | | |
| hash | | | | |
| algo | | | | |
| rithm | | | | |
| HMAC | HS3 | http://www.w3.org/2001/04/ | HmacSHA3 | 1.2.840.113 |
| using | 84 | xmldsig-more#hmac-sha384 | 84 | 549.2.10 |
| SHA-3 | | | | |
| 84 | | | | |
| hash | | | | |
| algo | | | | |
| rithm | | | | |
| HMAC | HS5 | http://www.w3.org/2001/04/ | HmacSHA5 | 1.2.840.113 |
| using | 12 | xmldsig-more#hmac-sha512 | 12 | 549.2.11 |
| SHA-5 | | | | |
| 12 | | | | |
| hash | | | | |
| algo | | | | |
| rithm | | | | |
| RSASS | RS2 | http://www.w3.org/2001/04/ | SHA256wi | 1.2.840.113 |
| A | 56 | xmldsig-more#rsa-sha256 | thRSA | 549.1.1.11 |
| usin | | | | |
| gSHA- | | | | |
| 256 | | | | |
| has | | | | |
| h alg | | | | |
| orith | | | | |
| m | | | | |
| RSASS | RS3 | http://www.w3.org/2001/04/ | SHA384wi | 1.2.840.113 |
| A | 84 | xmldsig-more#rsa-sha384 | thRSA | 549.1.1.12 |
| usin | | | | |
| gSHA- | | | | |
| 384 | | | | |
| has | | | | |
| h alg | | | | |
| orith | | | | |
| m | | | | |
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| RSASS | RS5 | http://www.w3.org/2001/04/ | SHA512wi | 1.2.840.113 |
| A | 12 | xmldsig-more#rsa-sha512 | thRSA | 549.1.1.13 |
| usin | | | | |
| gSHA- | | | | |
| 512 | | | | |
| has | | | | |
| h alg | | | | |
| orith | | | | |
| m | | | | |
| ECDSA | ES2 | http://www.w3.org/2001/04/ | SHA256wi | 1.2.840.100 |
| using | 56 | xmldsig-more#ecdsa-sha256 | thECDSA | 45.4.3.2 |
| P-256 | | | | |
| curve | | | | |
| and | | | | |
| SHA-2 | | | | |
| 56 | | | | |
| hash | | | | |
| algo | | | | |
| rithm | | | | |
| ECDSA | ES3 | http://www.w3.org/2001/04/ | SHA384wi | 1.2.840.100 |
| using | 84 | xmldsig-more#ecdsa-sha384 | thECDSA | 45.4.3.3 |
| P-384 | | | | |
| curve | | | | |
| and | | | | |
| SHA-3 | | | | |
| 84 | | | | |
| hash | | | | |
| algo | | | | |
| rithm | | | | |
| ECDSA | ES5 | http://www.w3.org/2001/04/ | SHA512wi | 1.2.840.100 |
| using | 12 | xmldsig-more#ecdsa-sha512 | thECDSA | 45.4.3.4 |
| P-521 | | | | |
| curve | | | | |
| and | | | | |
| SHA-5 | | | | |
| 12 | | | | |
| hash | | | | |
| algo | | | | |
| rithm | | | | |
+-------+-----+----------------------------+----------+-------------+
Appendix B. Encryption Algorithm Identifier Cross-Reference
This appendix contains a table cross-referencing the "alg"
(algorithm) and "enc" (encryption method) values used in this
specification with the equivalent identifiers used by other standards
and software packages. See XML Encryption
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[W3C.REC-xmlenc-core-20021210], XML Encryption 1.1
[W3C.CR-xmlenc-core1-20120313], and Java Cryptography Architecture
[JCA] for more information about the names defined by those
documents.
For the composite algorithms "A128CBC+HS256" and "A256CBC+HS512", the
corresponding AES CBC algorithm identifiers are listed.
+----------+--------+--------------------------+--------------------+
| Algorith | JWE | XML ENC | JCA |
| m | | | |
+----------+--------+--------------------------+--------------------+
| RSAES-PK | RSA1_5 | http://www.w3.org/2001/0 | RSA/ECB/PKCS1Paddi |
| CS1-V1_5 | | 4/xmlenc#rsa-1_5 | ng |
| RSAES | RSA-OA | http://www.w3.org/2001/0 | RSA/ECB/OAEPWithSH |
| using | EP | 4/xmlenc#rsa-oaep-mgf1p | A-1AndMGF1Padding |
| Optimal | | | |
| Asymmetr | | | |
| ic | | | |
| Encrypt | | | |
| ion | | | |
| Paddin | | | |
| g (OAEP) | | | |
| Elliptic | ECDH-E | http://www.w3.org/2009/x | |
| Curve | S | mlenc11#ECDH-ES | |
| Diffie-H | | | |
| ellman | | | |
| Ephemer | | | |
| alStatic | | | |
| Advanced | A128KW | http://www.w3.org/2001/0 | |
| Encrypti | | 4/xmlenc#kw-aes128 | |
| on | | | |
| Standar | | | |
| d(AES) | | | |
| Key Wra | | | |
| pAlgorit | | | |
| hmusing | | | |
| 128 bi | | | |
| t keys | | | |
| AES Key | A256KW | http://www.w3.org/2001/0 | |
| Wrap | | 4/xmlenc#kw-aes256 | |
| Algorith | | | |
| musing | | | |
| 256 bit | | | |
| keys | | | |
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| AES in | A128CB | http://www.w3.org/2001/0 | AES/CBC/PKCS5Paddi |
| Cipher | C+HS25 | 4/xmlenc#aes128-cbc | ng |
| Block | 6 | | |
| Chaining | | | |
| (CBC) | | | |
| mode | | | |
| with | | | |
| PKCS #5 | | | |
| padding | | | |
| using | | | |
| 128 bit | | | |
| keys | | | |
| AES in | A256CB | http://www.w3.org/2001/0 | AES/CBC/PKCS5Paddi |
| CBC mode | C+HS51 | 4/xmlenc#aes256-cbc | ng |
| with | 2 | | |
| PKCS #5 | | | |
| padding | | | |
| using | | | |
| 256 bit | | | |
| keys | | | |
| AES in | A128GC | http://www.w3.org/2009/x | AES/GCM/NoPadding |
| Galois/C | M | mlenc11#aes128-gcm | |
| ounter | | | |
| Mode | | | |
| (GCM) | | | |
| using | | | |
| 128 bit | | | |
| keys | | | |
| AES GCM | A256GC | http://www.w3.org/2009/x | AES/GCM/NoPadding |
| using | M | mlenc11#aes256-gcm | |
| 256 bit | | | |
| keys | | | |
+----------+--------+--------------------------+--------------------+
Appendix C. Acknowledgements
Solutions for signing and encrypting JSON content were previously
explored by Magic Signatures [MagicSignatures], JSON Simple Sign
[JSS], Canvas Applications [CanvasApp], JSON Simple Encryption [JSE],
and JavaScript Message Security Format [I-D.rescorla-jsms], all of
which influenced this draft. Dirk Balfanz, John Bradley, Yaron Y.
Goland, John Panzer, Nat Sakimura, and Paul Tarjan all made
significant contributions to the design of this specification and its
related specifications.
Jim Schaad and Karen O'Donoghue chaired the JOSE working group and
Sean Turner and Stephen Farrell served as Security area directors
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during the creation of this specification.
Appendix D. Open Issues
[[ to be removed by the RFC editor before publication as an RFC ]]
The following items remain to be considered or done in this draft:
o No known open issues.
Appendix E. Document History
[[ to be removed by the RFC editor before publication as an RFC ]]
-06
o Removed the "int" and "kdf" parameters and defined the new
composite AEAD algorithms "A128CBC+HS256" and "A256CBC+HS512" to
replace the former uses of AES CBC, which required the use of
separate integrity and key derivation functions.
o Included additional values in the Concat KDF calculation -- the
desired output size and the algorithm value, and optionally
PartyUInfo and PartyVInfo values. Added the optional header
parameters "apu" (agreement PartyUInfo), "apv" (agreement
PartyVInfo), "epu" (encryption PartyUInfo), and "epv" (encryption
PartyVInfo).
o Changed the name of the JWK RSA exponent parameter from "exp" to
"xpo" so as to allow the potential use of the name "exp" for a
future extension that might define an expiration parameter for
keys. (The "exp" name is already used for this purpose in the JWT
specification.)
o Applied changes made by the RFC Editor to RFC 6749's registry
language to this specification.
-05
o Support both direct encryption using a shared or agreed upon
symmetric key, and the use of a shared or agreed upon symmetric
key to key wrap the CMK. Specifically, added the "alg" values
"dir", "ECDH-ES+A128KW", and "ECDH-ES+A256KW" to finish filling in
this set of capabilities.
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o Updated open issues.
-04
o Added text requiring that any leading zero bytes be retained in
base64url encoded key value representations for fixed-length
values.
o Added this language to Registration Templates: "This name is case
sensitive. Names that match other registered names in a case
insensitive manner SHOULD NOT be accepted."
o Described additional open issues.
o Applied editorial suggestions.
-03
o Always use a 128 bit "authentication tag" size for AES GCM,
regardless of the key size.
o Specified that use of a 128 bit IV is REQUIRED with AES CBC. It
was previously RECOMMENDED.
o Removed key size language for ECDSA algorithms, since the key size
is implied by the algorithm being used.
o Stated that the "int" key size must be the same as the hash output
size (and not larger, as was previously allowed) so that its size
is defined for key generation purposes.
o Added the "kdf" (key derivation function) header parameter to
provide crypto agility for key derivation. The default KDF
remains the Concat KDF with the SHA-256 digest function.
o Clarified that the "mod" and "exp" values are unsigned.
o Added Implementation Requirements columns to algorithm tables and
Implementation Requirements entries to algorithm registries.
o Changed AES Key Wrap to RECOMMENDED.
o Moved registries JSON Web Signature and Encryption Header
Parameters and JSON Web Signature and Encryption Type Values to
the JWS specification.
o Moved JSON Web Key Parameters registry to the JWK specification.
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o Changed registration requirements from RFC Required to
Specification Required with Expert Review.
o Added Registration Template sections for defined registries.
o Added Registry Contents sections to populate registry values.
o No longer say "the UTF-8 representation of the JWS Secured Input
(which is the same as the ASCII representation)". Just call it
"the ASCII representation of the JWS Secured Input".
o Added "Collision Resistant Namespace" to the terminology section.
o Numerous editorial improvements.
-02
o For AES GCM, use the "additional authenticated data" parameter to
provide integrity for the header, encrypted key, and ciphertext
and use the resulting "authentication tag" value as the JWE
Integrity Value.
o Defined minimum required key sizes for algorithms without
specified key sizes.
o Defined KDF output key sizes.
o Specified the use of PKCS #5 padding with AES CBC.
o Generalized text to allow key agreement to be employed as an
alternative to key wrapping or key encryption.
o Clarified that ECDH-ES is a key agreement algorithm.
o Required implementation of AES-128-KW and AES-256-KW.
o Removed the use of "A128GCM" and "A256GCM" for key wrapping.
o Removed "A512KW" since it turns out that it's not a standard
algorithm.
o Clarified the relationship between "typ" header parameter values
and MIME types.
o Generalized language to refer to Message Authentication Codes
(MACs) rather than Hash-based Message Authentication Codes (HMACs)
unless in a context specific to HMAC algorithms.
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o Established registries: JSON Web Signature and Encryption Header
Parameters, JSON Web Signature and Encryption Algorithms, JSON Web
Signature and Encryption "typ" Values, JSON Web Key Parameters,
and JSON Web Key Algorithm Families.
o Moved algorithm-specific definitions from JWK to JWA.
o Reformatted to give each member definition its own section
heading.
-01
o Moved definition of "alg":"none" for JWSs here from the JWT
specification since this functionality is likely to be useful in
more contexts that just for JWTs.
o Added Advanced Encryption Standard (AES) Key Wrap Algorithm using
512 bit keys ("A512KW").
o Added text "Alternatively, the Encoded JWS Signature MAY be
base64url decoded to produce the JWS Signature and this value can
be compared with the computed HMAC value, as this comparison
produces the same result as comparing the encoded values".
o Corrected the Magic Signatures reference.
o Made other editorial improvements suggested by JOSE working group
participants.
-00
o Created the initial IETF draft based upon
draft-jones-json-web-signature-04 and
draft-jones-json-web-encryption-02 with no normative changes.
o Changed terminology to no longer call both digital signatures and
HMACs "signatures".
Author's Address
Michael B. Jones
Microsoft
Email: mbj@microsoft.com
URI: http://self-issued.info/
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