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JOSE Working Group M. Jones
Internet-Draft Microsoft
Intended status: Standards Track May 12, 2012
Expires: November 13, 2012
JSON Web Algorithms (JWA)
draft-ietf-jose-json-web-algorithms-02
Abstract
The JSON Web Algorithms (JWA) specification enumerates cryptographic
algorithms and identifiers to be used with the JSON Web Signature
(JWS) and JSON Web Encryption (JWE) specifications.
Requirements Language
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 RFC 2119 [RFC2119].
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 http://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 November 13, 2012.
Copyright Notice
Copyright (c) 2012 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Cryptographic Algorithms for JWS . . . . . . . . . . . . . . . 4
3.1. "alg" (Algorithm) Header Parameter Values for JWS . . . . 4
3.2. MAC with HMAC SHA-256, HMAC SHA-384, or HMAC SHA-512 . . . 5
3.3. Digital Signature with RSA SHA-256, RSA SHA-384, or
RSA SHA-512 . . . . . . . . . . . . . . . . . . . . . . . 6
3.4. Digital Signature with ECDSA P-256 SHA-256, ECDSA
P-384 SHA-384, or ECDSA P-521 SHA-512 . . . . . . . . . . 7
3.5. Creating a Plaintext JWS . . . . . . . . . . . . . . . . . 9
3.6. Additional Digital Signature/MAC Algorithms and
Parameters . . . . . . . . . . . . . . . . . . . . . . . . 9
4. Cryptographic Algorithms for JWE . . . . . . . . . . . . . . . 9
4.1. "alg" (Algorithm) Header Parameter Values for JWE . . . . 9
4.2. "enc" (Encryption Method) Header Parameter Values for
JWE . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.3. "int" (Integrity Algorithm) Header Parameter Values
for JWE . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.4. Key Encryption with RSA using RSA-PKCS1-1.5 Padding . . . 11
4.5. Key Encryption with RSA using Optimal Asymmetric
Encryption Padding (OAEP) . . . . . . . . . . . . . . . . 11
4.6. Key Agreement with Elliptic Curve Diffie-Hellman
Ephemeral Static (ECDH-ES) . . . . . . . . . . . . . . . . 12
4.7. Key Encryption with AES Key Wrap . . . . . . . . . . . . . 12
4.8. Plaintext Encryption with AES Cipher Block Chaining
(CBC) Mode . . . . . . . . . . . . . . . . . . . . . . . . 12
4.9. Plaintext Encryption with AES Galois/Counter Mode (GCM) . 12
4.10. Integrity Calculation with HMAC SHA-256, HMAC SHA-384,
or HMAC SHA-512 . . . . . . . . . . . . . . . . . . . . . 13
4.11. Additional Encryption Algorithms and Parameters . . . . . 13
5. Cryptographic Algorithms for JWK . . . . . . . . . . . . . . . 13
5.1. "alg" (Algorithm Family) Parameter Values for JWK . . . . 14
5.2. JWK Parameters for Elliptic Curve Keys . . . . . . . . . . 14
5.2.1. "crv" (Curve) Parameter . . . . . . . . . . . . . . . 14
5.2.2. "x" (X Coordinate) Parameter . . . . . . . . . . . . . 14
5.2.3. "y" (Y Coordinate) Parameter . . . . . . . . . . . . . 14
5.3. JWK Parameters for RSA Keys . . . . . . . . . . . . . . . 14
5.3.1. "mod" (Modulus) Parameter . . . . . . . . . . . . . . 15
5.3.2. "exp" (Exponent) Parameter . . . . . . . . . . . . . . 15
5.4. Additional Key Algorithm Families and Parameters . . . . . 15
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6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
6.1. JSON Web Signature and Encryption Header Parameters
Registry . . . . . . . . . . . . . . . . . . . . . . . . . 15
6.2. JSON Web Signature and Encryption Algorithms Registry . . 15
6.3. JSON Web Signature and Encryption "typ" Values Registry . 16
6.4. JSON Web Key Parameters Registry . . . . . . . . . . . . . 16
6.5. JSON Web Key Algorithm Families Registry . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
8. Open Issues and Things To Be Done (TBD) . . . . . . . . . . . 17
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . . 18
Appendix A. Digital Signature/MAC Algorithm Identifier
Cross-Reference . . . . . . . . . . . . . . . . . . . 19
Appendix B. Encryption Algorithm Identifier Cross-Reference . . . 21
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 25
Appendix D. Document History . . . . . . . . . . . . . . . . . . 25
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 26
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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] and JSON Web Encryption (JWE) [JWE] specifications.
Enumerating the algorithms and identifiers for them in this
specification, rather than in the JWS and JWE 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. This specification also describes the semantics and
operations that are specific to these algorithms and algorithm
families.
2. Terminology
This specification uses the terminology defined by the JSON Web
Signature (JWS) [JWS] and JSON Web Encryption (JWE) [JWE]
specifications.
3. Cryptographic Algorithms for JWS
JWS uses cryptographic algorithms to digitally sign or MAC 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 Parameter | Digital Signature or MAC Algorithm |
| Value | |
+--------------------+----------------------------------------------+
| HS256 | HMAC using SHA-256 hash algorithm |
| HS384 | HMAC using SHA-384 hash algorithm |
| HS512 | HMAC using SHA-512 hash algorithm |
| RS256 | RSA using SHA-256 hash algorithm |
| RS384 | RSA using SHA-384 hash algorithm |
| RS512 | RSA using SHA-512 hash algorithm |
| ES256 | ECDSA using P-256 curve and SHA-256 hash |
| | algorithm |
| ES384 | ECDSA using P-384 curve and SHA-384 hash |
| | algorithm |
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| ES512 | ECDSA using P-521 curve and SHA-512 hash |
| | algorithm |
| none | No digital signature or MAC value included |
+--------------------+----------------------------------------------+
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.
Of these algorithms, only HMAC SHA-256 and "none" MUST be implemented
by conforming JWS implementations. It is RECOMMENDED that
implementations also support the RSA SHA-256 and ECDSA P-256 SHA-256
algorithms. Support for other algorithms and key sizes is OPTIONAL.
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 cryptographic hash functions as
defined in FIPS 180-3 [FIPS.180-3]. 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 as follows:
1. Apply the HMAC SHA-256 algorithm to the bytes of the UTF-8
representation of the JWS Secured Input (which is the same as the
ASCII representation) using the shared key to produce an HMAC
value.
2. Base64url encode the resulting HMAC value.
The output is the Encoded JWS Signature for that JWS.
The HMAC SHA-256 MAC for a JWS is validated as follows:
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1. Apply the HMAC SHA-256 algorithm to the bytes of the UTF-8
representation of the JWS Secured Input (which is the same as the
ASCII representation) of the JWS using the shared key.
2. Base64url encode the resulting HMAC value.
3. If the Encoded JWS Signature and the base64url encoded HMAC value
exactly match, then one has confirmation that the shared key was
used to generate the HMAC on the JWS and that the contents of the
JWS have not be tampered with.
4. If the validation fails, the JWS MUST be rejected.
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.
Securing content with the HMAC SHA-384 and HMAC SHA-512 algorithms is
performed identically to the procedure for HMAC SHA-256 - just with
correspondingly larger minimum key sizes and result values.
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 RFC 3447 [RFC3447], Section 8.2
(commonly known as PKCS#1), using SHA-256, SHA-384, or SHA-512 as the
hash function. The RSASSA-PKCS1-v1_5 algorithm is described in FIPS
186-3 [FIPS.186-3], Section 5.5, and the SHA-256, SHA-384, and SHA-
512 cryptographic hash functions are defined in FIPS 180-3
[FIPS.180-3]. 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.
Note that 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, for interoperability
reasons, this specification does use RSASSA-PKCS1 because it commonly
implemented.
The RSA SHA-256 digital signature is generated as follows:
1. Generate a digital signature of the bytes of the UTF-8
representation of the JWS Secured Input (which is the same as the
ASCII representation) using RSASSA-PKCS1-V1_5-SIGN and the SHA-
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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:
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 UTF-8 representation of the JWS Secured
Input (which is the same as the ASCII representation) 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 with
correspondingly larger result values.
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) is defined by
FIPS 186-3 [FIPS.186-3]. ECDSA 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 also
defined in FIPS 186-3. 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.
A key of size 160 bits or larger MUST be used with these algorithms.
The ECDSA P-256 SHA-256 digital signature is generated as follows:
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1. Generate a digital signature of the bytes of the UTF-8
representation of the JWS Secured Input (which is the same as the
ASCII representation) using ECDSA P-256 SHA-256 with the desired
private key. The output will be the EC point (R, S), where R and
S are unsigned integers.
2. Turn R and S into byte arrays in big endian order. Each array
will be 32 bytes long.
3. Concatenate the two byte arrays in the order R and then S.
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.
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 UTF-8 representation of the JWS Secured
Input (which is the same as the ASCII representation), 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.
The ECDSA validator will then determine if the digital signature is
valid, given the inputs. 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.
The consequence of this is that one must validate an ECDSA digital
signature by submitting the previously specified inputs to an ECDSA
validator.
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 with correspondingly larger result values.
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3.5. Creating a Plaintext JWS
To support use cases where the content is secured by a means other
than a digital signature or MAC value, JWSs MAY also be created
without them. These are called "Plaintext JWSs". 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 defined in
the IANA JSON Web Signature and Encryption Algorithms registry
Section 6.2 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 Section 6.1. 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 | Key Encryption or Agreement Algorithm |
| Parameter | |
| Value | |
+-----------+-------------------------------------------------------+
| RSA1_5 | RSA using RSA-PKCS1-1.5 padding, as defined in RFC |
| | 3447 [RFC3447] |
| RSA-OAEP | RSA using Optimal Asymmetric Encryption Padding |
| | (OAEP), as defined in RFC 3447 [RFC3447] |
| ECDH-ES | Elliptic Curve Diffie-Hellman Ephemeral Static, as |
| | defined in RFC 6090 [RFC6090], and using the Concat |
| | KDF, as defined in Section 5.8.1 of [NIST.800-56A], |
| | where the Digest Method is SHA-256 and all OtherInfo |
| | parameters are the empty bit string |
| A128KW | Advanced Encryption Standard (AES) Key Wrap Algorithm |
| | using 128 bit keys, as defined in RFC 3394 [RFC3394] |
| A256KW | Advanced Encryption Standard (AES) Key Wrap Algorithm |
| | using 256 bit keys, as defined in RFC 3394 [RFC3394] |
+-----------+-------------------------------------------------------+
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 | Block Encryption Algorithm |
| Parameter | |
| Value | |
+-----------+-------------------------------------------------------+
| A128CBC | Advanced Encryption Standard (AES) using 128 bit keys |
| | in Cipher Block Chaining (CBC) mode using PKCS #5 |
| | padding, as defined in [FIPS.197] and [NIST.800-38A] |
| A256CBC | Advanced Encryption Standard (AES) using 256 bit keys |
| | in Cipher Block Chaining (CBC) mode using PKCS #5 |
| | padding, as defined in [FIPS.197] and [NIST.800-38A] |
| A128GCM | Advanced Encryption Standard (AES) using 128 bit keys |
| | in Galois/Counter Mode (GCM), as defined in |
| | [FIPS.197] and [NIST.800-38D] |
| A256GCM | Advanced Encryption Standard (AES) using 256 bit keys |
| | in Galois/Counter Mode (GCM), as defined in |
| | [FIPS.197] and [NIST.800-38D] |
+-----------+-------------------------------------------------------+
See Appendix B for a table cross-referencing the encryption "alg"
(algorithm) and "enc" (encryption method) values used in this
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specification with the equivalent identifiers used by other standards
and software packages.
Of these "alg" and "enc" algorithms, only RSA-PKCS1-1.5 with 2048 bit
keys, AES-128-KW, AES-256-KW, AES-128-CBC, and AES-256-CBC MUST be
implemented by conforming JWE implementations. It is RECOMMENDED
that implementations also support ECDH-ES with 256 bit keys, AES-128-
GCM, and AES-256-GCM. Support for other algorithms and key sizes is
OPTIONAL.
4.3. "int" (Integrity Algorithm) Header Parameter Values for JWE
The table below is the set of "int" (integrity algorithm) header
parameter values defined by this specification for use with JWE.
Note that these are the HMAC SHA subset of the "alg" (algorithm)
header parameter values defined for use with JWS Section 3.1. />
+---------------------+-----------------------------------+
| int Parameter Value | Algorithm |
+---------------------+-----------------------------------+
| HS256 | HMAC using SHA-256 hash algorithm |
| HS384 | HMAC using SHA-384 hash algorithm |
| HS512 | HMAC using SHA-512 hash algorithm |
+---------------------+-----------------------------------+
Of these "int" algorithms, only HMAC SHA-256 MUST be implemented by
conforming JWE implementations. It is RECOMMENDED that
implementations also support the RSA SHA-256 and ECDSA P-256 SHA-256
algorithms.
4.4. Key Encryption with RSA using RSA-PKCS1-1.5 Padding
This section defines the specifics of encrypting a JWE CMK with RSA
using RSA-PKCS1-1.5 padding, as defined in RFC 3447 [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.
4.5. Key Encryption with RSA using Optimal Asymmetric Encryption
Padding (OAEP)
This section defines the specifics of encrypting a JWE CMK with RSA
using Optimal Asymmetric Encryption Padding (OAEP), as defined in RFC
3447 [RFC3447]. 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.
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4.6. Key Agreement with Elliptic Curve Diffie-Hellman Ephemeral Static
(ECDH-ES)
This section defines the specifics of agreeing upon a JWE CMK with
Elliptic Curve Diffie-Hellman Ephemeral Static, as defined in RFC
6090 [RFC6090], and using the Concat KDF, as defined in Section 5.8.1
of [NIST.800-56A], where the Digest Method is SHA-256 and all
OtherInfo parameters are the empty bit string. The "alg" header
parameter value "ECDH-ES" is used in this case.
A key of size 160 bits or larger MUST be used for the Elliptic Curve
keys used with this algorithm. The output of the Concat KDF MUST be
a key of the same length as that used by the "enc" algorithm.
An "epk" (ephemeral public key) value MUST only be used for a single
key agreement transaction.
4.7. 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 using 128 or
256 bit keys, as defined in RFC 3394 [RFC3394]. The "alg" header
parameter values "A128KW" or "A256KW" are used in this case.
4.8. Plaintext Encryption with AES Cipher Block Chaining (CBC) Mode
This section defines the specifics of encrypting the JWE Plaintext
with Advanced Encryption Standard (AES) in Cipher Block Chaining
(CBC) mode using PKCS #5 padding using 128 or 256 bit keys, as
defined in [FIPS.197] and [NIST.800-38A]. The "enc" header parameter
values "A128CBC" or "A256CBC" are used in this case.
Use of an Initialization Vector (IV) of size 128 bits is RECOMMENDED
with this algorithm.
4.9. Plaintext Encryption with AES Galois/Counter Mode (GCM)
This section defines the specifics of encrypting the JWE Plaintext
with Advanced Encryption Standard (AES) in Galois/Counter Mode (GCM)
using 128 or 256 bit keys, as defined in [FIPS.197] and
[NIST.800-38D]. The "enc" header parameter values "A128GCM" or
"A256GCM" are used in this case.
Use of an Initialization Vector (IV) of size 96 bits is REQUIRED with
this algorithm.
The "additional authenticated data" parameter value for the
encryption is the concatenation of the Encoded JWE Header, a period
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('.') character, and the Encoded JWE Encrypted Key.
The requested size of the "authentication tag" output MUST be the
same as the key size (for instance, 128 bits for "A128GCM").
As GCM is an AEAD algorithm, the JWE Integrity Value is set to be the
"authentication tag" value produced by the encryption.
4.10. Integrity Calculation with HMAC SHA-256, HMAC SHA-384, or HMAC
SHA-512
This section defines the specifics of computing a JWE Integrity Value
with HMAC SHA-256, HMAC SHA-384, or HMAC SHA-512 as defined in FIPS
180-3 [FIPS.180-3]. The "int" header parameter values "HS256",
"HS384", or "HS512" are used in this case.
A key of the same size as the hash output (for instance, 256 bits for
"HS256") or larger MUST be used with this algorithm.
4.11. Additional Encryption Algorithms and Parameters
Additional algorithms MAY be used to protect JWEs with corresponding
"alg" (algorithm), "enc" (encryption method), and "int" (integrity
algorithm) header parameter values being defined to refer to them.
New "alg", "enc", and "int" header parameter values SHOULD either be
defined in the IANA JSON Web Signature and Encryption Algorithms
registry Section 6.2 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", "enc", and "int" 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 Section 6.1. 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 JSON data structure that represents a
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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 Value | Algorithm Family |
+---------------------+----------------------------------------+
| EC | Elliptic Curve [FIPS.186-3] key family |
| RSA | RSA [RFC3447] key family |
+---------------------+----------------------------------------+
5.2. JWK Parameters for Elliptic Curve Keys
JWKs can represent Elliptic Curve [FIPS.186-3] 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. Values defined by this specification are "P-256", "P-384"
and "P-521". Additional "crv" values MAY be used, provided they are
understood by implementations using that Elliptic Curve key. The
"crv" value is case sensitive. Its value MUST be a 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.
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.
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:
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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 big endian representation.
5.3.2. "exp" (Exponent) Parameter
The "exp" (exponent) member contains the exponent value for the RSA
public key. It is represented as the base64url encoding of the
value's big endian representation.
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 defined in the IANA JSON Web Key Algorithm
Families registry Section 6.5 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 defined in the
IANA JSON Web Key Parameters registry Section 6.4 or be a URI that
contains a collision resistant namespace.
6. IANA Considerations
6.1. JSON Web Signature and Encryption Header Parameters Registry
This specification establishes the IANA JSON Web Signature and
Encryption Header Parameters registry for reserved JWS and JWE header
parameter names. Inclusion in the registry is RFC Required in the
RFC 5226 [RFC5226] sense. The registry records the reserved header
parameter name and a reference to the RFC that defines it. This
specification registers the header parameter names defined in JSON
Web Signature (JWS) [JWS], Section 4.1 and JSON Web Encryption (JWE)
[JWE], Section 4.1.
6.2. 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), "enc" (encryption method), and "int" (integrity
algorithm) header parameters. Inclusion in the registry is RFC
Required in the RFC 5226 [RFC5226] sense. The registry records the
algorithm usage "alg", "enc", or "int", the value, and a pointer to
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the RFC that defines it. This specification registers the values
defined in Section 3.1, Section 4.1, Section 4.2, and Section 4.3.
6.3. JSON Web Signature and Encryption "typ" Values Registry
This specification establishes the IANA JSON Web Signature and
Encryption "typ" Values registry for values of the JWS and JWE "typ"
(type) header parameter. Inclusion in the registry is RFC Required
in the RFC 5226 [RFC5226] sense. It is RECOMMENDED that all
registered "typ" values also register a MIME Media Type RFC 2045
[RFC2045] that the registered value is a short name for. The
registry records the "typ" value, the MIME type value that it is an
abbreviation for (if any), and a pointer to the RFC that defines it.
MIME Media Type RFC 2045 [RFC2045] values MUST NOT be directly
registered as new "typ" values; rather, new "typ" values MAY be
registered as short names for MIME types.
6.4. JSON Web Key Parameters Registry
This specification establishes the IANA JSON Web Key Parameters
registry for reserved JWK parameter names. Inclusion in the registry
is RFC Required in the RFC 5226 [RFC5226] sense. The registry
records the reserved parameter name and a reference to the RFC that
defines it. This specification registers the parameter names defined
in JSON Web Key (JWK) [JWK], Section 4.2, JSON Web Encryption (JWE)
[JWE], Section 4.1, Section 5.2, and Section 5.3.
6.5. 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. Inclusion in the registry is RFC Required in the RFC 5226
[RFC5226] sense. The registry records the "alg" value and a pointer
to the RFC that defines it. This specification registers the values
defined in Section 5.1.
7. Security Considerations
The security considerations in the JWS, JWE, and JWK specifications
also 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.
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8. Open Issues and Things To Be Done (TBD)
The following items remain to be done in this draft:
o Find values for encryption algorithm cross-reference table
currently listed as "TBD" or determine that they do not exist.
9. References
9.1. Normative References
[FIPS.180-3]
National Institute of Standards and Technology, "Secure
Hash Standard (SHS)", FIPS PUB 180-3, October 2008.
[FIPS.186-3]
National Institute of Standards and Technology, "Digital
Signature Standard (DSS)", FIPS PUB 186-3, June 2009.
[FIPS.197]
National Institute of Standards and Technology (NIST),
"Advanced Encryption Standard (AES)", FIPS PUB 197,
November 2001.
[JWE] Jones, M., Rescorla, E., and J. Hildebrand, "JSON Web
Encryption (JWE)", May 2012.
[JWK] Jones, M., "JSON Web Key (JWK)", May 2012.
[JWS] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", May 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
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800-56A, March 2007.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[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
(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.
[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.
9.2. 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",
September 2010.
[MagicSignatures]
Panzer (editor), J., Laurie, B., and D. Balfanz, "Magic
Signatures", January 2011.
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[RFC3275] Eastlake, D., Reagle, J., and D. Solo, "(Extensible Markup
Language) XML-Signature Syntax and Processing", RFC 3275,
March 2002.
[W3C.CR-xmldsig-core2-20120124]
Eastlake, D., Reagle, J., Yiu, K., Solo, D., Datta, P.,
Hirsch, F., Cantor, S., and T. Roessler, "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., Roessler, T., and F. Hirsch,
"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.
+-------+-----+----------------------------+----------+-------------+
| 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 | | | | |
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| 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 | | | | |
| RSA | RS2 | http://www.w3.org/2001/04/ | SHA256wi | 1.2.840.113 |
| using | 56 | xmldsig-more#rsa-sha256 | thRSA | 549.1.1.11 |
| SHA-2 | | | | |
| 56 | | | | |
| hash | | | | |
| algo | | | | |
| rithm | | | | |
| RSA | RS3 | http://www.w3.org/2001/04/ | SHA384wi | 1.2.840.113 |
| using | 84 | xmldsig-more#rsa-sha384 | thRSA | 549.1.1.12 |
| SHA-3 | | | | |
| 84 | | | | |
| hash | | | | |
| algo | | | | |
| rithm | | | | |
| RSA | RS5 | http://www.w3.org/2001/04/ | SHA512wi | 1.2.840.113 |
| using | 12 | xmldsig-more#rsa-sha512 | thRSA | 549.1.1.13 |
| SHA-5 | | | | |
| 12 | | | | |
| hash | | | | |
| algo | | | | |
| rithm | | | | |
| 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 | | | | |
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| 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
[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.
+---------+-------+---------------------------+---------------------+
| Algorit | JWE | XML ENC | JCA |
| hm | | | |
+---------+-------+---------------------------+---------------------+
| RSA | RSA1_ | http://www.w3.org/2001/04 | RSA/ECB/PKCS1Paddin |
| using | 5 | /xmlenc#rsa-1_5 | g |
| RSA-PKC | | | |
| S1-1.5 | | | |
| paddin | | | |
| g | | | |
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| RSA | RSA-O | http://www.w3.org/2001/04 | RSA/ECB/OAEPWithSHA |
| using | AEP | /xmlenc#rsa-oaep-mgf1p | -1AndMGF1Padding |
| Optimal | | | |
| Asymmet | | | |
| ric | | | |
| Encryp | | | |
| tion | | | |
| Paddi | | | |
| ng(OAEP | | | |
| ) | | | |
| Ellipti | ECDH- | http://www.w3.org/2009/xm | TBD |
| cCurve | ES | lenc11#ECDH-ES | |
| Diffie | | | |
| -Hellma | | | |
| n Ephem | | | |
| eral | | | |
| Stat | | | |
| ic | | | |
| Advance | A128K | http://www.w3.org/2001/04 | TBD |
| d | W | /xmlenc#kw-aes128 | |
| Encryp | | | |
| tion | | | |
| Stand | | | |
| ard(AES | | | |
| ) Key | | | |
| Wrap | | | |
| Algo | | | |
| rithm R | | | |
| FC 339 | | | |
| 4 [RF | | | |
| C3394] | | | |
| using12 | | | |
| 8 bitke | | | |
| ys | | | |
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| Advance | A256K | http://www.w3.org/2001/04 | TBD |
| d | W | /xmlenc#kw-aes256 | |
| Encryp | | | |
| tion | | | |
| Stand | | | |
| ard(AES | | | |
| ) Key | | | |
| Wrap | | | |
| Algo | | | |
| rithm R | | | |
| FC 339 | | | |
| 4 [RF | | | |
| C3394] | | | |
| using25 | | | |
| 6 bitke | | | |
| ys | | | |
| Advance | A128C | http://www.w3.org/2001/04 | AES/CBC/PKCS5Paddin |
| d | BC | /xmlenc#aes128-cbc | g |
| Encryp | | | |
| tion | | | |
| Stand | | | |
| ard(AES | | | |
| ) usin | | | |
| g 128 | | | |
| bitkeys | | | |
| inCiph | | | |
| er Bloc | | | |
| k Chai | | | |
| ning(CB | | | |
| C) mod | | | |
| e usi | | | |
| ng PKC | | | |
| S #5pad | | | |
| ding | | | |
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| Advance | A256C | http://www.w3.org/2001/04 | AES/CBC/PKCS5Paddin |
| d | BC | /xmlenc#aes256-cbc | g |
| Encryp | | | |
| tion | | | |
| Stand | | | |
| ard(AES | | | |
| ) usin | | | |
| g 256 | | | |
| bitkeys | | | |
| inCiph | | | |
| er Bloc | | | |
| k Chai | | | |
| ning(CB | | | |
| C) mod | | | |
| e usi | | | |
| ng PKC | | | |
| S #5pad | | | |
| ding | | | |
| Advance | A128G | http://www.w3.org/2009/xm | AES/GCM/NoPadding |
| d | CM | lenc11#aes128-gcm | |
| Encryp | | | |
| tion | | | |
| Stand | | | |
| ard(AES | | | |
| ) usin | | | |
| g 128 | | | |
| bitkeys | | | |
| inGalo | | | |
| is/Coun | | | |
| ter Mod | | | |
| e (GC | | | |
| M) | | | |
| Advance | A256G | http://www.w3.org/2009/xm | AES/GCM/NoPadding |
| d | CM | lenc11#aes256-gcm | |
| Encryp | | | |
| tion | | | |
| Stand | | | |
| ard(AES | | | |
| ) usin | | | |
| g 256 | | | |
| bitkeys | | | |
| inGalo | | | |
| is/Coun | | | |
| ter Mod | | | |
| e (GC | | | |
| M) | | | |
+---------+-------+---------------------------+---------------------+
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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.
Appendix D. Document History
-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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