OAuth Working Group M. Jones
Internet-Draft Microsoft
Intended status: Standards Track J. Bradley
Expires: July 2, 2014 Ping Identity
N. Sakimura
NRI
December 29, 2013

JSON Web Token (JWT)
draft-ietf-oauth-json-web-token-14

Abstract

JSON Web Token (JWT) is a compact URL-safe means of representing claims to be transferred between two parties. The claims in a JWT are encoded as a JavaScript Object Notation (JSON) object that is used as the payload of a JSON Web Signature (JWS) structure or as the plaintext of a JSON Web Encryption (JWE) structure, enabling the claims to be digitally signed or MACed and/or encrypted.

The suggested pronunciation of JWT is the same as the English word "jot".

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/.

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This Internet-Draft will expire on July 2, 2014.

Copyright Notice

Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

1. Introduction

JSON Web Token (JWT) is a compact claims representation format intended for space constrained environments such as HTTP Authorization headers and URI query parameters. JWTs encode claims to be transmitted as a JavaScript Object Notation (JSON) [RFC4627] object that is used as the payload of a JSON Web Signature (JWS) [JWS] structure or as the plaintext of a JSON Web Encryption (JWE) [JWE] structure, enabling the claims to be digitally signed or MACed and/or encrypted. JWTs are always represented using the JWS Compact Serialization or the JWE Compact Serialization.

The suggested pronunciation of JWT is the same as the English word "jot".

1.1. Notational Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in Key words for use in RFCs to Indicate Requirement Levels [RFC2119]. If these words are used without being spelled in uppercase then they are to be interpreted with their normal natural language meanings.

2. Terminology

JSON Web Token (JWT)
A string representing a set of claims as a JSON object that is encoded in a JWS or JWE, enabling the claims to be digitally signed or MACed and/or encrypted.
Base64url Encoding
Base64 encoding using the URL- and filename-safe character set defined in Section 5 of RFC 4648 [RFC4648], with all trailing '=' characters omitted (as permitted by Section 3.2). (See Appendix C of [JWS] for notes on implementing base64url encoding without padding.)
JWT Header
A JSON object that describes the cryptographic operations applied to the JWT. When the JWT is digitally signed or MACed, the JWT Header is a JWS Header. When the JWT is encrypted, the JWT Header is a JWE Header.
Header Parameter
A name/value pair that is member of the JWT Header.
Header Parameter Name
The name of a member of the JWT Header.
Header Parameter Value
The value of a member of the JWT Header.
JWT Claims Set
A JSON object that contains the Claims conveyed by the JWT.
Claim
A piece of information asserted about a subject. A Claim is represented as a name/value pair consisting of a Claim Name and a Claim Value.
Claim Name
The name portion of a Claim representation. A Claim Name is always a string.
Claim Value
The value portion of a Claim representation. A Claim Value can be any JSON value.
Encoded JWT Header
Base64url encoding of the JWT Header.
Nested JWT
A JWT in which nested signing and/or encryption are employed. In nested JWTs, a JWT is used as the payload or plaintext value of an enclosing JWS or JWE structure, respectively.
Plaintext JWT
A JWT whose Claims are not integrity protected or encrypted.
Collision-Resistant Name
A name in a namespace that enables names to be allocated in a manner such that they are highly unlikely to collide with other names. Examples of collision-resistant namespaces include: Domain Names, Object Identifiers (OIDs) as defined in the ITU-T X.660 and X.670 Recommendation series, and Universally Unique IDentifiers (UUIDs) [RFC4122]. When using an administratively delegated namespace, the definer of a name needs to take reasonable precautions to ensure they are in control of the portion of the namespace they use to define the name.
StringOrURI
A JSON string value, with the additional requirement that while arbitrary string values MAY be used, any value containing a ":" character MUST be a URI [RFC3986]. StringOrURI values are compared as case-sensitive strings with no transformations or canonicalizations applied.
IntDate
A JSON numeric value representing the number of seconds from 1970-01-01T0:0:0Z UTC until the specified UTC date/time. See RFC 3339 [RFC3339] for details regarding date/times in general and UTC in particular.

3. JSON Web Token (JWT) Overview

JWTs represent a set of claims as a JSON object that is encoded in a JWS and/or JWE structure. This JSON object is the JWT Claims Set. As per RFC 4627 [RFC4627] Section 2.2, the JSON object consists of zero or more name/value pairs (or members), where the names are strings and the values are arbitrary JSON values. These members are the claims represented by the JWT.

The member names within the JWT Claims Set are referred to as Claim Names. The corresponding values are referred to as Claim Values.

The contents of the JWT Header describe the cryptographic operations applied to the JWT Claims Set. If the JWT Header is a JWS Header, the JWT is represented as a JWS, and the claims are digitally signed or MACed, with the JWT Claims Set being the JWS Payload. If the JWT Header is a JWE Header, the JWT is represented as a JWE, and the claims are encrypted, with the JWT Claims Set being the input Plaintext. A JWT may be enclosed in another JWE or JWS structure to create a Nested JWT, enabling nested signing and encryption to be performed.

A JWT is represented as a sequence of URL-safe parts separated by period ('.') characters. Each part contains a base64url encoded value. The number of parts in the JWT is dependent upon the representation of the resulting JWS or JWE object using the JWS Compact Serialization or the JWE Compact Serialization.

3.1. Example JWT

The following example JWT Header declares that the encoded object is a JSON Web Token (JWT) and the JWT is a JWS that is MACed using the HMAC SHA-256 algorithm:

  {"typ":"JWT",
   "alg":"HS256"}

The following octet sequence is the UTF-8 representation of the JWT Header/JWS Header above:

[123, 34, 116, 121, 112, 34, 58, 34, 74, 87, 84, 34, 44, 13, 10, 32, 34, 97, 108, 103, 34, 58, 34, 72, 83, 50, 53, 54, 34, 125]

Base64url encoding the octets of the UTF-8 representation of the JWT Header yields this Encoded JWT Header value (which is also the underlying encoded JWS Header value):

  eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9

The following is an example of a JWT Claims Set:

  {"iss":"joe",
   "exp":1300819380,
   "http://example.com/is_root":true}

The following octet sequence, which is the UTF-8 representation of the JWT Claims Set above, is the JWS Payload:

[123, 34, 105, 115, 115, 34, 58, 34, 106, 111, 101, 34, 44, 13, 10, 32, 34, 101, 120, 112, 34, 58, 49, 51, 48, 48, 56, 49, 57, 51, 56, 48, 44, 13, 10, 32, 34, 104, 116, 116, 112, 58, 47, 47, 101, 120, 97, 109, 112, 108, 101, 46, 99, 111, 109, 47, 105, 115, 95, 114, 111, 111, 116, 34, 58, 116, 114, 117, 101, 125]

Base64url encoding the JWS Payload yields this encoded JWS Payload (with line breaks for display purposes only):

  eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly
  9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ

Computing the MAC of the encoded JWS Header and encoded JWS Payload with the HMAC SHA-256 algorithm and base64url encoding the HMAC value in the manner specified in [JWS], yields this encoded JWS Signature:

  dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk

Concatenating these encoded parts in this order with period ('.') characters between the parts yields this complete JWT (with line breaks for display purposes only):

  eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
  .
  eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
  cGxlLmNvbS9pc19yb290Ijp0cnVlfQ
  .
  dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk

This computation is illustrated in more detail in Appendix A.1 of [JWS]. See Appendix A.1 for an example of an encrypted JWT.

4. JWT Claims

The JWT Claims Set represents a JSON object whose members are the claims conveyed by the JWT. The Claim Names within a JWT Claims Set MUST be unique; recipients MUST either reject JWTs with duplicate Claim Names or use a JSON parser that returns only the lexically last duplicate member name, as specified in Section 15.12 (The JSON Object) of ECMAScript 5.1 [ECMAScript].

The set of claims that a JWT must contain to be considered valid is context-dependent and is outside the scope of this specification. Specific applications of JWTs will require implementations to understand and process some claims in particular ways. However, in the absence of such requirements, all claims that are not understood by implementations SHOULD be ignored.

There are three classes of JWT Claim Names: Registered Claim Names, Public Claim Names, and Private Claim Names.

4.1. Registered Claim Names

The following Claim Names are registered in the IANA JSON Web Token Claims registry defined in Section 10.1. None of the claims defined below are intended to be mandatory to use, but rather, provide a starting point for a set of useful, interoperable claims. All the names are short because a core goal of JWTs is for the representation to be compact.

4.1.1. "iss" (Issuer) Claim

The iss (issuer) claim identifies the principal that issued the JWT. The processing of this claim is generally application specific. The iss value is a case-sensitive string containing a StringOrURI value. Use of this claim is OPTIONAL.

4.1.2. "sub" (Subject) Claim

The sub (subject) claim identifies the principal that is the subject of the JWT. The Claims in a JWT are normally statements about the subject. The subject value MAY be scoped to be locally unique in the context of the issuer or MAY be globally unique. The processing of this claim is generally application specific. The sub value is a case-sensitive string containing a StringOrURI value. Use of this claim is OPTIONAL.

4.1.3. "aud" (Audience) Claim

The aud (audience) claim identifies the audiences that the JWT is intended for. Each principal intended to process the JWT MUST identify itself with a value in audience claim. If the principal processing the claim does not identify itself with a value in the aud claim, then the JWT MUST be rejected. In the general case, the aud value is an array of case-sensitive strings, each containing a StringOrURI value. In the special case when the JWT has one audience, the aud value MAY be a single case-sensitive string containing a StringOrURI value. The interpretation of audience values is generally application specific. Use of this claim is OPTIONAL.

4.1.4. "exp" (Expiration Time) Claim

The exp (expiration time) claim identifies the expiration time on or after which the JWT MUST NOT be accepted for processing. The processing of the exp claim requires that the current date/time MUST be before the expiration date/time listed in the exp claim. Implementers MAY provide for some small leeway, usually no more than a few minutes, to account for clock skew. Its value MUST be a number containing an IntDate value. Use of this claim is OPTIONAL.

4.1.5. "nbf" (Not Before) Claim

The nbf (not before) claim identifies the time before which the JWT MUST NOT be accepted for processing. The processing of the nbf claim requires that the current date/time MUST be after or equal to the not-before date/time listed in the nbf claim. Implementers MAY provide for some small leeway, usually no more than a few minutes, to account for clock skew. Its value MUST be a number containing an IntDate value. Use of this claim is OPTIONAL.

4.1.6. "iat" (Issued At) Claim

The iat (issued at) claim identifies the time at which the JWT was issued. This claim can be used to determine the age of the JWT. Its value MUST be a number containing an IntDate value. Use of this claim is OPTIONAL.

4.1.7. "jti" (JWT ID) Claim

The jti (JWT ID) claim provides a unique identifier for the JWT. The identifier value MUST be assigned in a manner that ensures that there is a negligible probability that the same value will be accidentally assigned to a different data object. The jti claim can be used to prevent the JWT from being replayed. The jti value is a case-sensitive string. Use of this claim is OPTIONAL.

4.2. Public Claim Names

Claim Names can be defined at will by those using JWTs. However, in order to prevent collisions, any new Claim Name should either be registered in the IANA JSON Web Token Claims registry defined in Section 10.1 or be a Public Name: a value that contains a Collision-Resistant Name. In each case, the definer of the name or value needs to take reasonable precautions to make sure they are in control of the part of the namespace they use to define the Claim Name.

4.3. Private Claim Names

A producer and consumer of a JWT MAY agree to use Claim Names that are Private Names: names that are not Registered Claim Names Section 4.1 or Public Claim Names Section 4.2. Unlike Public Claim Names, Private Claim Names are subject to collision and should be used with caution.

5. JWT Header

The members of the JSON object represented by the JWT Header describe the cryptographic operations applied to the JWT and optionally, additional properties of the JWT. The member names within the JWT Header are referred to as Header Parameter Names. These names MUST be unique; recipients MUST either reject JWTs with duplicate Header Parameter Names or use a JSON parser that returns only the lexically last duplicate member name, as specified in Section 15.12 (The JSON Object) of ECMAScript 5.1 [ECMAScript]. The corresponding values are referred to as Header Parameter Values.

JWS Header Parameters are defined by [JWS]. JWE Header Parameters are defined by [JWE]. This specification further specifies the use of the following Header Parameter in both the cases where the JWT is a JWS and where it is a JWE.

5.1. "typ" (Type) Header Parameter

The typ (type) Header Parameter defined by [JWS] and [JWE] is used to declare the MIME Media Type [IANA.MediaTypes] of this complete JWT in contexts where this is useful to the application. This parameter has no effect upon the JWT processing. If present, it is RECOMMENDED that its value be JWT to indicate that this object is a JWT. While media type names are not case-sensitive, it is RECOMMENDED that JWT always be spelled using uppercase characters for compatibility with legacy implementations. Use of this Header Parameter is OPTIONAL.

5.2. "cty" (Content Type) Header Parameter

The cty (content type) Header Parameter defined by [JWS] and [JWE] is used by this specification to convey structural information about the JWT.

In the normal case where nested signing or encryption operations are not employed, the use of this Header Parameter is NOT RECOMMENDED. In the case that nested signing or encryption is employed, this Header Parameter MUST be present; in this case, the value MUST be JWT, to indicate that a Nested JWT is carried in this JWT. While media type names are not case-sensitive, it is RECOMMENDED that JWT always be spelled using uppercase characters for compatibility with legacy implementations. See Appendix A.2 for an example of a Nested JWT.

5.3. Replicating Claims as Header Parameters

In some applications using encrypted JWTs, it is useful to have an unencrypted representation of some Claims. This might be used, for instance, in application processing rules to determine whether and how to process the JWT before it is decrypted.

This specification allows Claims present in the JWT Claims Set to be replicated as Header Parameters in a JWT that is a JWE, as needed by the application. If such replicated Claims are present, the application receiving them SHOULD verify that their values are identical. It is the responsibility of the application to ensure that only claims that are safe to be transmitted in an unencrypted manner are replicated as Header Parameter Values in the JWT.

This specification registers the iss (issuer), sub (subject), and aud (audience) Header Parameter Names for the purpose of providing unencrypted replicas of these Claims in encrypted JWTs for applications that need them. Other specifications MAY similarly register other names that are registered Claim Names as Header Parameter Names, as needed.

6. Plaintext JWTs

To support use cases where the JWT content is secured by a means other than a signature and/or encryption contained within the JWT (such as a signature on a data structure containing the JWT), JWTs MAY also be created without a signature or encryption. A plaintext JWT is a JWS using the none JWS alg Header Parameter Value defined in JSON Web Algorithms (JWA) [JWA]; it is a JWS with the empty string for its JWS Signature value.

6.1. Example Plaintext JWT

The following example JWT Header declares that the encoded object is a Plaintext JWT:

  {"alg":"none"}

Base64url encoding the octets of the UTF-8 representation of the JWT Header yields this Encoded JWT Header:

  eyJhbGciOiJub25lIn0

The following is an example of a JWT Claims Set:

  {"iss":"joe",
   "exp":1300819380,
   "http://example.com/is_root":true}

Base64url encoding the octets of the UTF-8 representation of the JWT Claims Set yields this encoded JWS Payload (with line breaks for display purposes only):

  eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
  cGxlLmNvbS9pc19yb290Ijp0cnVlfQ

The encoded JWS Signature is the empty string.

Concatenating these encoded parts in this order with period ('.') characters between the parts yields this complete JWT (with line breaks for display purposes only):

  eyJhbGciOiJub25lIn0
  .
  eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
  cGxlLmNvbS9pc19yb290Ijp0cnVlfQ
  .

7. Rules for Creating and Validating a JWT

To create a JWT, one MUST perform these steps. The order of the steps is not significant in cases where there are no dependencies between the inputs and outputs of the steps.

  1. Create a JWT Claims Set containing the desired claims. Note that white space is explicitly allowed in the representation and no canonicalization need be performed before encoding.
  2. Let the Message be the octets of the UTF-8 representation of the JWT Claims Set.
  3. Create a JWT Header containing the desired set of Header Parameters. The JWT MUST conform to either the [JWS] or [JWE] specifications. Note that white space is explicitly allowed in the representation and no canonicalization need be performed before encoding.
  4. Base64url encode the octets of the UTF-8 representation of the JWT Header. Let this be the Encoded JWT Header.
  5. Depending upon whether the JWT is a JWS or JWE, there are two cases:

  6. If a nested signing or encryption operation will be performed, let the Message be the JWS or JWE, and return to Step 3, using a cty (content type) value of JWT in the new JWT Header created in that step.
  7. Otherwise, let the resulting JWT be the JWS or JWE.

When validating a JWT the following steps MUST be taken. The order of the steps is not significant in cases where there are no dependencies between the inputs and outputs of the steps. If any of the listed steps fails then the JWT MUST be rejected for processing.

  1. The JWT MUST contain at least one period ('.') character.
  2. Let the Encoded JWT Header be the portion of the JWT before the first period ('.') character.
  3. The Encoded JWT Header MUST be successfully base64url decoded following the restriction given in this specification that no padding characters have been used.
  4. The resulting JWT Header MUST be completely valid JSON syntax conforming to RFC 4627 [RFC4627].
  5. The resulting JWT Header MUST be validated to only include parameters and values whose syntax and semantics are both understood and supported or that are specified as being ignored when not understood.
  6. Determine whether the JWT is a JWS or a JWE using any of the methods described in Section 9 of [JWE].
  7. Depending upon whether the JWT is a JWS or JWE, there are two cases:

  8. If the JWT Header contains a cty (content type) value of JWT, then the Message is a JWT that was the subject of nested signing or encryption operations. In this case, return to Step 1, using the Message as the JWT.
  9. Otherwise, let the JWT Claims Set be the Message.
  10. The JWT Claims Set MUST be completely valid JSON syntax conforming to RFC 4627 [RFC4627].

7.1. String Comparison Rules

Processing a JWT inevitably requires comparing known strings to values in JSON objects. For example, in checking what the algorithm is, the Unicode string encoding alg will be checked against the member names in the JWT Header to see if there is a matching Header Parameter Name.

Comparisons between JSON strings and other Unicode strings MUST be performed by comparing Unicode code points without normalization, as specified in the String Comparison Rules in Section 5.3 of [JWS].

8. Cryptographic Algorithms

JWTs use JSON Web Signature (JWS) [JWS] and JSON Web Encryption (JWE) [JWE] to sign and/or encrypt the contents of the JWT.

Of the signature and MAC algorithms specified in JSON Web Algorithms (JWA) [JWA], only HMAC SHA-256 (HS256) and none MUST be implemented by conforming JWT implementations. It is RECOMMENDED that implementations also support RSASSA-PKCS1-V1_5 with the SHA-256 hash algorithm (RS256) and ECDSA using the P-256 curve and the SHA-256 hash algorithm (ES256). Support for other algorithms and key sizes is OPTIONAL.

If an implementation provides encryption capabilities, of the encryption algorithms specified in [JWA], only RSAES-PKCS1-V1_5 with 2048 bit keys (RSA1_5), AES Key Wrap with 128 and 256 bit keys (A128KW and A256KW), and the composite authenticated encryption algorithm using AES CBC and HMAC SHA-2 (A128CBC-HS256 and A256CBC-HS512) MUST be implemented by conforming implementations. It is RECOMMENDED that implementations also support using ECDH-ES to agree upon a key used to wrap the Content Encryption Key (ECDH-ES+A128KW and ECDH-ES+A256KW) and AES in Galois/Counter Mode (GCM) with 128 bit and 256 bit keys (A128GCM and A256GCM). Support for other algorithms and key sizes is OPTIONAL.

9. URI for Declaring that Content is a JWT

This specification registers the URN urn:ietf:params:oauth:token-type:jwt for use by applications that declare content types using URIs (rather than, for instance, MIME Media Types) to indicate that the content referred to is a JWT.

10. IANA Considerations

10.1. JSON Web Token Claims Registry

This specification establishes the IANA JSON Web Token Claims registry for JWT Claim Names. The registry records the Claim Name and a reference to the specification that defines it. This specification registers the Claim Names defined in Section 4.1.

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 the RFC Editor: The name of the mailing list should be determined in consultation with the IESG and IANA. Suggested name: jwt-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. Registration requests that are undetermined for a period longer than 21 days can be brought to the IESG's attention (using the iesg@iesg.org mailing list) for resolution.

Criteria that should be applied by the Designated Expert(s) includes determining whether the proposed registration duplicates existing functionality, determining whether it is likely to be of general applicability or whether it is useful only for a single application, and whether the registration makes sense.

IANA must only accept registry updates from the Designated Expert(s) and should direct all requests for registration to the review mailing list.

It is suggested that multiple Designated Experts be appointed who are able to represent the perspectives of different applications using this specification, in order to enable broadly-informed review of registration decisions. In cases where a registration decision could be perceived as creating a conflict of interest for a particular Expert, that Expert should defer to the judgment of the other Expert(s).

10.1.1. Registration Template

Claim Name:

The name requested (e.g., "example"). Because a core goal of this specification is for the resulting representations to be compact, it is RECOMMENDED that the name be short -- not to exceed 8 characters without a compelling reason to do so. This name is case-sensitive. Names may not match other registered names in a case-insensitive manner unless the Designated Expert(s) state that there is a compelling reason to allow an exception in this particular case.
Claim Description:

Brief description of the Claim (e.g., "Example description").
Change Controller:

For Standards Track RFCs, state "IESG". For others, give the name of the responsible party. Other details (e.g., postal address, email address, home page URI) may also be included.
Specification Document(s):

Reference to the document(s) that specify the parameter, preferably including URI(s) that can be used to retrieve copies of the document(s). An indication of the relevant sections may also be included but is not required.

10.1.2. Initial Registry Contents

10.2. Sub-Namespace Registration of urn:ietf:params:oauth:token-type:jwt

10.2.1. Registry Contents

This specification registers the value token-type:jwt in the IANA urn:ietf:params:oauth registry established in An IETF URN Sub-Namespace for OAuth [RFC6755], which can be used to indicate that the content is a JWT.

10.3. Media Type Registration

10.3.1. Registry Contents

This specification registers the application/jwt Media Type [RFC2046] in the MIME Media Types registry [IANA.MediaTypes], which can be used to indicate that the content is a JWT.

10.4. Registration of JWE Header Parameter Names

This specification registers specific Claim Names defined in Section 4.1 in the IANA JSON Web Signature and Encryption Header Parameters registry defined in [JWS] for use by Claims replicated as Header Parameters, per Section 5.3.

10.4.1. Registry Contents

11. Security Considerations

All of the security issues faced by any cryptographic application must be faced by a JWT/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.

All the security considerations in the JWS specification also apply to JWT, as do the JWE security considerations when encryption is employed. In particular, the JWS JSON Security Considerations and Unicode Comparison Security Considerations apply equally to the JWT Claims Set in the same manner that they do to the JWS Header.

While syntactically, the signing and encryption operations for Nested JWTs may be applied in any order, normally senders should sign the message and then encrypt the result (thus encrypting the signature). This prevents attacks in which the signature is stripped, leaving just an encrypted message, as well as providing privacy for the signer. Furthermore, signatures over encrypted text are not considered valid in many jurisdictions.

Note that potential concerns about security issues related to the order of signing and encryption operations are already addressed by the underlying JWS and JWE specifications; in particular, because JWE only supports the use of authenticated encryption algorithms, cryptographic concerns about the potential need to sign after encryption that apply in many contexts do not apply to this specification.

12. References

12.1. Normative References

[ECMAScript] Ecma International, "ECMAScript Language Specification, 5.1 Edition", ECMA 262, June 2011.
[IANA.MediaTypes] Internet Assigned Numbers Authority (IANA), "MIME Media Types", 2005.
[JWA] Jones, M., "JSON Web Algorithms (JWA)", Internet-Draft draft-ietf-jose-json-web-algorithms, December 2013.
[JWE] Jones, M., Rescorla, E. and J. Hildebrand, "JSON Web Encryption (JWE)", Internet-Draft draft-ietf-jose-json-web-encryption, December 2013.
[JWK] Jones, M., "JSON Web Key (JWK)", Internet-Draft draft-ietf-jose-json-web-key, December 2013.
[JWS] Jones, M., Bradley, J. and N. Sakimura, "JSON Web Signature (JWS)", Internet-Draft draft-ietf-jose-json-web-signature, December 2013.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, July 2002.
[RFC3986] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005.
[RFC4627] Crockford, D., "The application/json Media Type for JavaScript Object Notation (JSON)", RFC 4627, July 2006.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, October 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
[RFC6755] Campbell, B. and H. Tschofenig, "An IETF URN Sub-Namespace for OAuth", RFC 6755, October 2012.

12.2. Informative References

[CanvasApp] Facebook, , "Canvas Applications", 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.
[OASIS.saml-core-2.0-os] Cantor, S., Kemp, J., Philpott, R. and E. Maler, "Assertions and Protocol for the OASIS Security Assertion Markup Language (SAML) V2.0", OASIS Standard saml-core-2.0-os, March 2005.
[RFC3275] Eastlake, D., Reagle, J. and D. Solo, "(Extensible Markup Language) XML-Signature Syntax and Processing", RFC 3275, March 2002.
[RFC4122] Leach, P., Mealling, M. and R. Salz, "A Universally Unique IDentifier (UUID) URN Namespace", RFC 4122, July 2005.
[SWT] Hardt, D. and Y. Goland, "Simple Web Token (SWT)", Version 0.9.5.1, November 2009.
[W3C.CR-xml11-20021015] Cowan, J., "Extensible Markup Language (XML) 1.1", W3C CR CR-xml11-20021015, October 2002.
[W3C.REC-xml-c14n-20010315] Boyer, J., "Canonical XML Version 1.0", World Wide Web Consortium Recommendation REC-xml-c14n-20010315, March 2001.

Appendix A. JWT Examples

This section contains examples of JWTs. For other example JWTs, see Section 6.1 and Appendices A.1, A.2, and A.3 of [JWS].

A.1. Example Encrypted JWT

This example encrypts the same claims as used in Section 3.1 to the recipient using RSAES-PKCS1-V1_5 and AES_128_CBC_HMAC_SHA_256.

The following example JWE Header (with line breaks for display purposes only) declares that:

  {"alg":"RSA1_5","enc":"A128CBC-HS256"}

Other than using the octets of the UTF-8 representation of the JWT Claims Set from Section 3.1 as the plaintext value, the computation of this JWT is identical to the computation of the JWE in Appendix A.2 of [JWE], including the keys used.

The final result in this example (with line breaks for display purposes only) is:

  eyJhbGciOiJSU0ExXzUiLCJlbmMiOiJBMTI4Q0JDLUhTMjU2In0.
  QR1Owv2ug2WyPBnbQrRARTeEk9kDO2w8qDcjiHnSJflSdv1iNqhWXaKH4MqAkQtM
  oNfABIPJaZm0HaA415sv3aeuBWnD8J-Ui7Ah6cWafs3ZwwFKDFUUsWHSK-IPKxLG
  TkND09XyjORj_CHAgOPJ-Sd8ONQRnJvWn_hXV1BNMHzUjPyYwEsRhDhzjAD26ima
  sOTsgruobpYGoQcXUwFDn7moXPRfDE8-NoQX7N7ZYMmpUDkR-Cx9obNGwJQ3nM52
  YCitxoQVPzjbl7WBuB7AohdBoZOdZ24WlN1lVIeh8v1K4krB8xgKvRU8kgFrEn_a
  1rZgN5TiysnmzTROF869lQ.
  AxY8DCtDaGlsbGljb3RoZQ.
  MKOle7UQrG6nSxTLX6Mqwt0orbHvAKeWnDYvpIAeZ72deHxz3roJDXQyhxx0wKaM
  HDjUEOKIwrtkHthpqEanSBNYHZgmNOV7sln1Eu9g3J8.
  fiK51VwhsxJ-siBMR-YFiA

A.2. Example Nested JWT

This example shows how a JWT can be used as the payload of a JWE or JWS to create a Nested JWT. In this case, the JWT Claims Set is first signed, and then encrypted.

The inner signed JWT is identical to the example in Appendix A.2 of [JWS]. Therefore, its computation is not repeated here. This example then encrypts this inner JWT to the recipient using RSAES-PKCS1-V1_5 and AES_128_CBC_HMAC_SHA_256.

The following example JWE Header (with line breaks for display purposes only) declares that:

  {"alg":"RSA1_5","enc":"A128CBC-HS256","cty":"JWT"}

Base64url encoding the octets of the UTF-8 representation of the JWE Header yields this encoded JWE Header value:

  eyJhbGciOiJSU0ExXzUiLCJlbmMiOiJBMTI4Q0JDLUhTMjU2IiwiY3R5IjoiSldUIn0

The computation of this JWT is identical to the computation of the JWE in Appendix A.2 of [JWE], other than that different JWE Header, Plaintext, Initialization Vector, and Content Encryption Key values are used. (The RSA key used is the same.)

The Payload used is the octets of the ASCII representation of the JWT at the end of Appendix Section A.2.1 of [JWS] (with all whitespace and line breaks removed), which is a sequence of 458 octets.

The Initialization Vector value used is:

[82, 101, 100, 109, 111, 110, 100, 32, 87, 65, 32, 57, 56, 48, 53, 50]

This example uses the Content Encryption Key represented in JSON Web Key [JWK] format below:

  {"kty":"oct",
   "k":"GawgguFyGrWKav7AX4VKUg"
  }

The final result for this Nested JWT (with line breaks for display purposes only) is:

  eyJhbGciOiJSU0ExXzUiLCJlbmMiOiJBMTI4Q0JDLUhTMjU2IiwiY3R5IjoiSldU
  In0.
  g_hEwksO1Ax8Qn7HoN-BVeBoa8FXe0kpyk_XdcSmxvcM5_P296JXXtoHISr_DD_M
  qewaQSH4dZOQHoUgKLeFly-9RI11TG-_Ge1bZFazBPwKC5lJ6OLANLMd0QSL4fYE
  b9ERe-epKYE3xb2jfY1AltHqBO-PM6j23Guj2yDKnFv6WO72tteVzm_2n17SBFvh
  DuR9a2nHTE67pe0XGBUS_TK7ecA-iVq5COeVdJR4U4VZGGlxRGPLRHvolVLEHx6D
  YyLpw30Ay9R6d68YCLi9FYTq3hIXPK_-dmPlOUlKvPr1GgJzRoeC9G5qCvdcHWsq
  JGTO_z3Wfo5zsqwkxruxwA.
  UmVkbW9uZCBXQSA5ODA1Mg.
  VwHERHPvCNcHHpTjkoigx3_ExK0Qc71RMEParpatm0X_qpg-w8kozSjfNIPPXiTB
  BLXR65CIPkFqz4l1Ae9w_uowKiwyi9acgVztAi-pSL8GQSXnaamh9kX1mdh3M_TT
  -FZGQFQsFhu0Z72gJKGdfGE-OE7hS1zuBD5oEUfk0Dmb0VzWEzpxxiSSBbBAzP10
  l56pPfAtrjEYw-7ygeMkwBl6Z_mLS6w6xUgKlvW6ULmkV-uLC4FUiyKECK4e3WZY
  Kw1bpgIqGYsw2v_grHjszJZ-_I5uM-9RA8ycX9KqPRp9gc6pXmoU_-27ATs9XCvr
  ZXUtK2902AUzqpeEUJYjWWxSNsS-r1TJ1I-FMJ4XyAiGrfmo9hQPcNBYxPz3GQb2
  8Y5CLSQfNgKSGt0A4isp1hBUXBHAndgtcslt7ZoQJaKe_nNJgNliWtWpJ_ebuOpE
  l8jdhehdccnRMIwAmU1n7SPkmhIl1HlSOpvcvDfhUN5wuqU955vOBvfkBOh5A11U
  zBuo2WlgZ6hYi9-e3w29bR0C2-pp3jbqxEDw3iWaf2dc5b-LnR0FEYXvI_tYk5rd
  _J9N0mg0tQ6RbpxNEMNoA9QWk5lgdPvbh9BaO195abQ.
  AVO9iT5AV4CzvDJCdhSFlQ

Appendix B. Relationship of JWTs to SAML Assertions

SAML 2.0 [OASIS.saml-core-2.0-os] provides a standard for creating security tokens with greater expressivity and more security options than supported by JWTs. However, the cost of this flexibility and expressiveness is both size and complexity. SAML's use of XML [W3C.CR-xml11-20021015] and XML DSIG [RFC3275] contributes to the size of SAML assertions; its use of XML and especially XML Canonicalization [W3C.REC-xml-c14n-20010315] contributes to their complexity.

JWTs are intended to provide a simple security token format that is small enough to fit into HTTP headers and query arguments in URIs. It does this by supporting a much simpler token model than SAML and using the JSON [RFC4627] object encoding syntax. It also supports securing tokens using Message Authentication Codes (MACs) and digital signatures using a smaller (and less flexible) format than XML DSIG.

Therefore, while JWTs can do some of the things SAML assertions do, JWTs are not intended as a full replacement for SAML assertions, but rather as a token format to be used when ease of implementation or compactness are considerations.

SAML Assertions are always statements made by an entity about a subject. JWTs are often used in the same manner, with the entity making the statements being represented by the iss (issuer) claim, and the subject being represented by the sub (subject) claim. However, with these claims being optional, other uses of the JWT format are also permitted.

Appendix C. Relationship of JWTs to Simple Web Tokens (SWTs)

Both JWTs and Simple Web Tokens SWT [SWT], at their core, enable sets of claims to be communicated between applications. For SWTs, both the claim names and claim values are strings. For JWTs, while claim names are strings, claim values can be any JSON type. Both token types offer cryptographic protection of their content: SWTs with HMAC SHA-256 and JWTs with a choice of algorithms, including signature, MAC, and encryption algorithms.

Appendix D. Acknowledgements

The authors acknowledge that the design of JWTs was intentionally influenced by the design and simplicity of Simple Web Tokens [SWT] and ideas for JSON tokens that Dick Hardt discussed within the OpenID community.

Solutions for signing JSON content were previously explored by Magic Signatures [MagicSignatures], JSON Simple Sign [JSS], and Canvas Applications [CanvasApp], all of which influenced this draft.

This specification is the work of the OAuth 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, Brian Campbell, Breno de Medeiros, Dick Hardt, Joe Hildebrand, Jeff Hodges, Edmund Jay, Yaron Y. Goland, Ben Laurie, James Manger, Prateek Mishra, Tony Nadalin, Axel Nennker, John Panzer, Emmanuel Raviart, David Recordon, Eric Rescorla, Jim Schaad, Paul Tarjan, Hannes Tschofenig, and Sean Turner.

Hannes Tschofenig and Derek Atkins chaired the OAuth working group and Sean Turner and Stephen Farrell served as Security area directors during the creation of this specification.

Appendix E. Document History

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Authors' Addresses

Michael B. Jones Microsoft EMail: mbj@microsoft.com URI: http://self-issued.info/
John Bradley Ping Identity EMail: ve7jtb@ve7jtb.com URI: http://www.thread-safe.com/
Nat Sakimura Nomura Research Institute EMail: n-sakimura@nri.co.jp URI: http://nat.sakimura.org/