JOSE Working Group | M.B. Jones |
Internet-Draft | Microsoft |
Intended status: Standards Track | December 28, 2012 |
Expires: July 01, 2013 |
JSON Web Algorithms (JWA)
draft-ietf-jose-json-web-algorithms-08
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.
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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 key types.
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.
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].
These terms defined by the JSON Web Signature (JWS) [JWS] specification are incorporated into this specification:
These terms defined by the JSON Web Encryption (JWE) [JWE] specification are incorporated into this specification:
These terms defined by the JSON Web Key (JWK) [JWK] specification are incorporated into this specification:
These terms are defined for use by this specification:
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.
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 Value | Digital Signature or MAC Algorithm | Implementation Requirements |
---|---|---|
HS256 | HMAC using SHA-256 hash algorithm | REQUIRED |
HS384 | HMAC using SHA-384 hash algorithm | OPTIONAL |
HS512 | HMAC using SHA-512 hash algorithm | OPTIONAL |
RS256 | RSASSA using SHA-256 hash algorithm | RECOMMENDED |
RS384 | RSASSA using SHA-384 hash algorithm | OPTIONAL |
RS512 | RSASSA using SHA-512 hash algorithm | OPTIONAL |
ES256 | ECDSA using P-256 curve and SHA-256 hash algorithm | RECOMMENDED+ |
ES384 | ECDSA using P-384 curve and SHA-384 hash algorithm | OPTIONAL |
ES512 | ECDSA using P-521 curve and SHA-512 hash algorithm | OPTIONAL |
none | No digital signature or MAC value included | REQUIRED |
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.
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 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].
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:
The output is the Encoded JWS Signature for that JWS.
The RSA SHA-256 digital signature for a JWS is validated as follows:
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].
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:
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:
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].
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 the empty string for its JWS Signature value.
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 value 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.
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.
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.
alg Parameter Value | Key Encryption or Agreement Algorithm | Implementation Requirements |
---|---|---|
RSA1_5 | RSAES-PKCS1-V1_5 [RFC3447] | REQUIRED |
RSA-OAEP | RSAES using Optimal Asymmetric Encryption Padding (OAEP) [RFC3447], with the default parameters specified by RFC 3447 in Section A.2.1 | OPTIONAL |
A128KW | Advanced Encryption Standard (AES) Key Wrap Algorithm [RFC3394] using 128 bit keys | RECOMMENDED |
A256KW | AES Key Wrap Algorithm using 256 bit keys | RECOMMENDED |
dir | Direct use of a shared symmetric key as the Content Master Key (CMK) for the block encryption step (rather than using the symmetric key to wrap the CMK) | RECOMMENDED |
ECDH-ES | Elliptic Curve Diffie-Hellman 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 | RECOMMENDED+ |
ECDH-ES+A128KW | Elliptic Curve Diffie-Hellman 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) | RECOMMENDED |
ECDH-ES+A256KW | Elliptic Curve Diffie-Hellman 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) | RECOMMENDED |
The use of "+" in the Implementation Requirements indicates that the requirement strength is likely to be increased in a future version of the specification.
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 Value | Block Encryption Algorithm | Implementation Requirements |
---|---|---|
A128CBC+HS256 | Composite Authenticated Encryption algorithm using 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 | REQUIRED |
A256CBC+HS512 | Composite Authenticated Encryption algorithm using 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 | REQUIRED |
A128GCM | AES in Galois/Counter Mode (GCM) [AES] [NIST.800-38D] using 128 bit keys | RECOMMENDED |
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.
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].
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].
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].
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.
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 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.
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:
This section defines two composite enc algorithms that perform plaintext encryption using non-Authenticated Encryption algorithms and add an integrity check calculation, so that the resulting composite algorithms perform Authenticated Encryption. 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].
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:
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].
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.
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, and the Encoded JWE Ciphertext. (Equivalently, this input value is the concatenation of the "additional authenticated data" value, a byte containing an ASCII period character, and the bytes of the ASCII representation of 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. (Equivalently, this value is the "authentication tag" output for the algorithm.) The same integrity calculation is performed during decryption. During decryption, the computed integrity value must match the received JWE Integrity Value.
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, per Section 5 of the JWE specification.) 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.
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].
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 parameter values SHOULD either be registered in the IANA JSON Web Signature and Encryption Algorithms registry Section 6.1 or be a value 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.
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 key types to be used for those public keys and the key type specific parameters for representing those keys.
The table below is the set of kty (key type) parameter values that are defined by this specification for use in JWKs.
kty Parameter Value | Key Type | Implementation Requirements |
---|---|---|
EC | Elliptic Curve [DSS] key type | RECOMMENDED+ |
RSA | RSA [RFC3447] key type | REQUIRED |
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 kty 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.
JWKs can represent Elliptic Curve [DSS] keys. In this case, the kty member value MUST be EC. Furthermore, these additional members MUST be present:
The crv (curve) member identifies the cryptographic curve used with the key. Curve values from [DSS] used by this specification are: crv values MAY be used, provided they are understood by implementations using that Elliptic Curve key. The crv value is a case sensitive string.
Additional
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.
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.
JWKs can represent RSA [RFC3447] keys. In this case, the kty member value MUST be RSA. Furthermore, these additional members MUST be present:
The n (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.
The e (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].
Public keys using additional key types MAY be represented using JWK data structures with corresponding kty (key type) parameter values being defined to refer to them. New kty parameter values SHOULD either be registered in the IANA JSON Web Key Types registry Section 6.2 or be a value that contains a Collision Resistant Namespace.
Likewise, parameters for representing keys for additional key types or additional key properties SHOULD either be registered in the IANA JSON Web Key Parameters registry [JWK] or be a value that contains a Collision Resistant Namespace.
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 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.
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.
This specification establishes the IANA JSON Web Key Types registry for values of the JWK kty (key type) parameter. The registry records the kty value and a reference to the specification that defines it. This specification registers the values defined in Section 5.1.
This specification registers the parameter names defined in Sections 5.2 and 5.3 in the IANA JSON Web Key Parameters registry [JWK].
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 and symmetric keys, 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 certificate to a trust anchor are advised to have some sort of cryptographic resource management system to prevent such attacks.
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.
Algorithm | JWS | XML DSIG | JCA | OID |
---|---|---|---|---|
HMAC using SHA-256 hash algorithm | HS256 | http://www.w3.org/2001/04/xmldsig-more#hmac-sha256 | HmacSHA256 | 1.2.840.113549.2.9 |
HMAC using SHA-384 hash algorithm | HS384 | http://www.w3.org/2001/04/xmldsig-more#hmac-sha384 | HmacSHA384 | 1.2.840.113549.2.10 |
HMAC using SHA-512 hash algorithm | HS512 | http://www.w3.org/2001/04/xmldsig-more#hmac-sha512 | HmacSHA512 | 1.2.840.113549.2.11 |
RSASSA using SHA-256 hash algorithm | RS256 | http://www.w3.org/2001/04/xmldsig-more#rsa-sha256 | SHA256withRSA | 1.2.840.113549.1.1.11 |
RSASSA using SHA-384 hash algorithm | RS384 | http://www.w3.org/2001/04/xmldsig-more#rsa-sha384 | SHA384withRSA | 1.2.840.113549.1.1.12 |
RSASSA using SHA-512 hash algorithm | RS512 | http://www.w3.org/2001/04/xmldsig-more#rsa-sha512 | SHA512withRSA | 1.2.840.113549.1.1.13 |
ECDSA using P-256 curve and SHA-256 hash algorithm | ES256 | http://www.w3.org/2001/04/xmldsig-more#ecdsa-sha256 | SHA256withECDSA | 1.2.840.10045.4.3.2 |
ECDSA using P-384 curve and SHA-384 hash algorithm | ES384 | http://www.w3.org/2001/04/xmldsig-more#ecdsa-sha384 | SHA384withECDSA | 1.2.840.10045.4.3.3 |
ECDSA using P-521 curve and SHA-512 hash algorithm | ES512 | http://www.w3.org/2001/04/xmldsig-more#ecdsa-sha512 | SHA512withECDSA | 1.2.840.10045.4.3.4 |
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.
For the composite algorithms A128CBC+HS256 and A256CBC+HS512, the corresponding AES CBC algorithm identifiers are listed.
Algorithm | JWE | XML ENC | JCA |
---|---|---|---|
RSAES-PKCS1-V1_5 | RSA1_5 | http://www.w3.org/2001/04/xmlenc#rsa-1_5 | RSA/ECB/PKCS1Padding |
RSAES using Optimal Asymmetric Encryption Padding (OAEP) | RSA-OAEP | http://www.w3.org/2001/04/xmlenc#rsa-oaep-mgf1p | RSA/ECB/OAEPWithSHA-1AndMGF1Padding |
Elliptic Curve Diffie-Hellman Ephemeral Static | ECDH-ES | http://www.w3.org/2009/xmlenc11#ECDH-ES | |
Advanced Encryption Standard (AES) Key Wrap Algorithm using 128 bit keys | A128KW | http://www.w3.org/2001/04/xmlenc#kw-aes128 | |
AES Key Wrap Algorithm using 256 bit keys | A256KW | http://www.w3.org/2001/04/xmlenc#kw-aes256 | |
AES in Cipher Block Chaining (CBC) mode with PKCS #5 padding using 128 bit keys | A128CBC+HS256 | http://www.w3.org/2001/04/xmlenc#aes128-cbc | AES/CBC/PKCS5Padding |
AES in CBC mode with PKCS #5 padding using 256 bit keys | A256CBC+HS512 | http://www.w3.org/2001/04/xmlenc#aes256-cbc | AES/CBC/PKCS5Padding |
AES in Galois/Counter Mode (GCM) using 128 bit keys | A128GCM | http://www.w3.org/2009/xmlenc11#aes128-gcm | AES/GCM/NoPadding |
AES GCM using 256 bit keys | A256GCM | http://www.w3.org/2009/xmlenc11#aes256-gcm | AES/GCM/NoPadding |
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.
This specification is the work of the JOSE Working Group, which includes dozens of active and dedicated participants. In particular, the following individuals contributed ideas, feedback, and wording that influenced this specification:
Dirk Balfanz, Richard Barnes, John Bradley, Brian Campbell, Breno de Medeiros, Yaron Y. Goland, Dick Hardt, Jeff Hodges, Edmund Jay, James Manger, Tony Nadalin, Axel Nennker, John Panzer, Emmanuel Raviart, Nat Sakimura, Jim Schaad, Hannes Tschofenig, and Sean Turner.
Jim Schaad and Karen O'Donoghue chaired the JOSE working group and Sean Turner and Stephen Farrell served as Security area directors during the creation of this specification.
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The following items remain to be considered or done in this draft:
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