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 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [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 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
2.  Terminology
3.  Cryptographic Algorithms for JWS
    3.1.  "alg" (Algorithm) Header Parameter Values for JWS
    3.2.  MAC with HMAC SHA-256, HMAC SHA-384, or HMAC SHA-512
    3.3.  Digital Signature with RSA SHA-256, RSA SHA-384, or RSA SHA-512
    3.4.  Digital Signature with ECDSA P-256 SHA-256, ECDSA P-384 SHA-384, or ECDSA P-521 SHA-512
    3.5.  Creating a Plaintext JWS
    3.6.  Additional Digital Signature/MAC Algorithms and Parameters
4.  Cryptographic Algorithms for JWE
    4.1.  "alg" (Algorithm) Header Parameter Values for JWE
    4.2.  "enc" (Encryption Method) Header Parameter Values for JWE
    4.3.  "int" (Integrity Algorithm) Header Parameter Values for JWE
    4.4.  Key Encryption with RSA using RSA-PKCS1-1.5 Padding
    4.5.  Key Encryption with RSA using Optimal Asymmetric Encryption Padding (OAEP)
    4.6.  Key Agreement with Elliptic Curve Diffie-Hellman Ephemeral Static (ECDH-ES)
    4.7.  Key Encryption with AES Key Wrap
    4.8.  Plaintext Encryption with AES Cipher Block Chaining (CBC) Mode
    4.9.  Plaintext Encryption with AES Galois/Counter Mode (GCM)
    4.10.  Integrity Calculation with HMAC SHA-256, HMAC SHA-384, or HMAC SHA-512
    4.11.  Additional Encryption Algorithms and Parameters
5.  Cryptographic Algorithms for JWK
    5.1.  "alg" (Algorithm Family) Parameter Values for JWK
    5.2.  JWK Parameters for Elliptic Curve Keys
        5.2.1.  "crv" (Curve) Parameter
        5.2.2.  "x" (X Coordinate) Parameter
        5.2.3.  "y" (Y Coordinate) Parameter
    5.3.  JWK Parameters for RSA Keys
        5.3.1.  "mod" (Modulus) Parameter
        5.3.2.  "exp" (Exponent) Parameter
    5.4.  Additional Key Algorithm Families and Parameters
6.  IANA Considerations
    6.1.  JSON Web Signature and Encryption Header Parameters Registry
    6.2.  JSON Web Signature and Encryption Algorithms Registry
    6.3.  JSON Web Signature and Encryption "typ" Values Registry
    6.4.  JSON Web Key Parameters Registry
    6.5.  JSON Web Key Algorithm Families Registry
7.  Security Considerations
8.  Open Issues and Things To Be Done (TBD)
9.  References
    9.1.  Normative References
    9.2.  Informative References
Appendix A.  Digital Signature/MAC Algorithm Identifier Cross-Reference
Appendix B.  Encryption Algorithm Identifier Cross-Reference
Appendix C.  Acknowledgements
Appendix D.  Document History
§  Author's Address

1.  Introduction

The JSON Web Algorithms (JWA) specification enumerates cryptographic algorithms and identifiers to be used with the JSON Web Signature (JWS) [JWS] (Jones, M., Bradley, J., and N. Sakimura, “JSON Web Signature (JWS),” May 2012.) and JSON Web Encryption (JWE) [JWE] (Jones, M., Rescorla, E., and J. Hildebrand, “JSON Web Encryption (JWE),” May 2012.) 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] (Jones, M., Bradley, J., and N. Sakimura, “JSON Web Signature (JWS),” May 2012.) and JSON Web Encryption (JWE) [JWE] (Jones, M., Rescorla, E., and J. Hildebrand, “JSON Web Encryption (JWE),” May 2012.) 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:

See Appendix A (Digital Signature/MAC Algorithm Identifier Cross-Reference) 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 (Krawczyk, H., Bellare, M., and R. Canetti, “HMAC: Keyed-Hashing for Message Authentication,” February 1997.) [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 (National Institute of Standards and Technology, “Secure Hash Standard (SHS),” October 2008.) [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:

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 (Jonsson, J. and B. Kaliski, “Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1,” February 2003.) [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 (National Institute of Standards and Technology, “Digital Signature Standard (DSS),” June 2009.) [FIPS.186‑3], Section 5.5, and the SHA-256, SHA-384, and SHA-512 cryptographic hash functions are defined in FIPS 180-3 (National Institute of Standards and Technology, “Secure Hash Standard (SHS),” October 2008.) [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 (Jonsson, J. and B. Kaliski, “Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1,” February 2003.) [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-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 (National Institute of Standards and Technology, “Digital Signature Standard (DSS),” June 2009.) [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:

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.

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 (JSON Web Signature and Encryption Algorithms Registry) or be a URI that contains a collision resistant namespace. In particular, it is permissible to use the algorithm identifiers defined in XML DSIG (Eastlake, D., Reagle, J., and D. Solo, “(Extensible Markup Language) XML-Signature Syntax and Processing,” March 2002.) [RFC3275], XML DSIG 2.0 (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,” January 2012.) [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 (JSON Web Signature and Encryption Header Parameters Registry). 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.

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.

See Appendix B (Encryption Algorithm Identifier Cross-Reference) 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.

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 ("alg" (Algorithm) Header Parameter Values for JWS). />

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 (Jonsson, J. and B. Kaliski, “Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1,” February 2003.) [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 (Jonsson, J. and B. Kaliski, “Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1,” February 2003.) [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.

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 (McGrew, D., Igoe, K., and M. Salter, “Fundamental Elliptic Curve Cryptography Algorithms,” February 2011.) [RFC6090], and using the Concat KDF, as defined in Section 5.8.1 of [NIST.800‑56A] (National Institute of Standards and Technology (NIST), “Recommendation for Pair-Wise Key Establishment Schemes Using Discrete Logarithm Cryptography (Revised),” March 2007.), 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 (Schaad, J. and R. Housley, “Advanced Encryption Standard (AES) Key Wrap Algorithm,” September 2002.) [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] (National Institute of Standards and Technology (NIST), “Advanced Encryption Standard (AES),” November 2001.) and [NIST.800‑38A] (National Institute of Standards and Technology (NIST), “Recommendation for Block Cipher Modes of Operation,” December 2001.). 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] (National Institute of Standards and Technology (NIST), “Advanced Encryption Standard (AES),” November 2001.) and [NIST.800‑38D] (National Institute of Standards and Technology (NIST), “Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC,” December 2001.). 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 ('.') 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 (National Institute of Standards and Technology, “Secure Hash Standard (SHS),” October 2008.) [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 (JSON Web Signature and Encryption Algorithms Registry) or be a URI that contains a collision resistant namespace. In particular, it is permissible to use the algorithm identifiers defined in XML Encryption (Eastlake, D. and J. Reagle, “XML Encryption Syntax and Processing,” December 2002.) [W3C.REC‑xmlenc‑core‑20021210], XML Encryption 1.1 (Eastlake, D., Reagle, J., Roessler, T., and F. Hirsch, “XML Encryption Syntax and Processing Version 1.1,” March 2012.) [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 (JSON Web Signature and Encryption Header Parameters Registry). 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] (Jones, M., “JSON Web Key (JWK),” May 2012.) is a JSON 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.

5.2.  JWK Parameters for Elliptic Curve Keys

JWKs can represent Elliptic Curve [FIPS.186‑3] (National Institute of Standards and Technology, “Digital Signature Standard (DSS),” June 2009.) 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] (Jonsson, J. and B. Kaliski, “Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1,” February 2003.) 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 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 (JSON Web Key Algorithm Families Registry) 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 (JSON Web Key Parameters Registry) 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 (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.) [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] (Jones, M., Bradley, J., and N. Sakimura, “JSON Web Signature (JWS),” May 2012.), Section 4.1 and JSON Web Encryption (JWE) [JWE] (Jones, M., Rescorla, E., and J. Hildebrand, “JSON Web Encryption (JWE),” May 2012.), 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 (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.) [RFC5226] sense. The registry records the algorithm usage alg, enc, or int, the value, and a pointer to the RFC that defines it. This specification registers the values defined in Section 3.1 ("alg" (Algorithm) Header Parameter Values for JWS), Section 4.1 ("alg" (Algorithm) Header Parameter Values for JWE), Section 4.2 ("enc" (Encryption Method) Header Parameter Values for JWE), and Section 4.3 ("int" (Integrity Algorithm) Header Parameter Values for JWE).

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 (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.) [RFC5226] sense. It is RECOMMENDED that all registered typ values also register a MIME Media Type RFC 2045 (Freed, N. and N. Borenstein, “Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies,” November 1996.) [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 (Freed, N. and N. Borenstein, “Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies,” November 1996.) [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 (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.) [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] (Jones, M., “JSON Web Key (JWK),” May 2012.), Section 4.2, JSON Web Encryption (JWE) [JWE] (Jones, M., Rescorla, E., and J. Hildebrand, “JSON Web Encryption (JWE),” May 2012.), Section 4.1, Section 5.2 (JWK Parameters for Elliptic Curve Keys), and Section 5.3 (JWK Parameters for RSA Keys).

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 (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.) [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 ("alg" (Algorithm Family) Parameter Values for JWK).

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.

8.  Open Issues and Things To Be Done (TBD)

The following items remain to be done in this draft:

• 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

9.2. Informative References

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 (Eastlake, D., Reagle, J., and D. Solo, “(Extensible Markup Language) XML-Signature Syntax and Processing,” March 2002.) [RFC3275], XML DSIG 2.0 (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,” January 2012.) [W3C.CR‑xmldsig‑core2‑20120124], and Java Cryptography Architecture (Oracle, “Java Cryptography Architecture,” 2011.) [JCA] for more information about the names defined by those documents.

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 (Eastlake, D. and J. Reagle, “XML Encryption Syntax and Processing,” December 2002.) [W3C.REC‑xmlenc‑core‑20021210], XML Encryption 1.1 (Eastlake, D., Reagle, J., Roessler, T., and F. Hirsch, “XML Encryption Syntax and Processing Version 1.1,” March 2012.) [W3C.CR‑xmlenc‑core1‑20120313], and Java Cryptography Architecture (Oracle, “Java Cryptography Architecture,” 2011.) [JCA] for more information about the names defined by those documents.

Appendix C.  Acknowledgements

Solutions for signing and encrypting JSON content were previously explored by Magic Signatures (Panzer (editor), J., Laurie, B., and D. Balfanz, “Magic Signatures,” January 2011.) [MagicSignatures], JSON Simple Sign (Bradley, J. and N. Sakimura (editor), “JSON Simple Sign,” September 2010.) [JSS], Canvas Applications (Facebook, “Canvas Applications,” 2010.) [CanvasApp], JSON Simple Encryption (Bradley, J. and N. Sakimura (editor), “JSON Simple Encryption,” September 2010.) [JSE], and JavaScript Message Security Format (Rescorla, E. and J. Hildebrand, “JavaScript Message Security Format,” March 2011.) [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

• 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.
• Defined minimum required key sizes for algorithms without specified key sizes.
• Defined KDF output key sizes.
• Specified the use of PKCS #5 padding with AES-CBC.
• Generalized text to allow key agreement to be employed as an alternative to key wrapping or key encryption.
• Clarified that ECDH-ES is a key agreement algorithm.
• Required implementation of AES-128-KW and AES-256-KW.
• Removed the use of A128GCM and A256GCM for key wrapping.
• Removed A512KW since it turns out that it's not a standard algorithm.
• Clarified the relationship between typ header parameter values and MIME types.
• 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.
• 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.
• Moved algorithm-specific definitions from JWK to JWA.
• Reformatted to give each member definition its own section heading.

-01

• 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.
• Added Advanced Encryption Standard (AES) Key Wrap Algorithm using 512 bit keys (A512KW).
• 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".
• Corrected the Magic Signatures reference.
• Made other editorial improvements suggested by JOSE working group participants.

-00

• Created the initial IETF draft based upon draft-jones-json-web-signature-04 and draft-jones-json-web-encryption-02 with no normative changes.
• Changed terminology to no longer call both digital signatures and HMACs "signatures".

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