Network Working Group M. Jones
Internet-Draft Microsoft
Intended status: Standards Track D. Balfanz
Expires: July 1, 2011 Google
J. Bradley
independent
Y. Goland
Microsoft
J. Panzer
Google
N. Sakimura
Nomura Research Institute
December 28, 2010
JSON Web Token (JWT)
draft-jones-json-web-token-00
Abstract
JSON Web Token (JWT) defines a token format that can encode claims
transferred between two parties. The claims in a JWT are encoded as
a JSON object that is digitally signed.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 1, 2011.
Copyright Notice
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Copyright (c) 2010 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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. JSON Web Token (JWT) Overview . . . . . . . . . . . . . . . . 6
3.1. Example JWT . . . . . . . . . . . . . . . . . . . . . . . 6
4. JWT Claims . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Reserved Claim Names . . . . . . . . . . . . . . . . . . . 7
4.2. Public Claim Names . . . . . . . . . . . . . . . . . . . . 9
4.3. Private Claim Names . . . . . . . . . . . . . . . . . . . 9
5. JWT Envelope . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1. Reserved Envelope Parameter Names . . . . . . . . . . . . 10
5.2. Public Envelope Parameter Names . . . . . . . . . . . . . 12
5.3. Private Envelope Parameter Names . . . . . . . . . . . . . 12
6. General Rules for Creating and Validating a JWT . . . . . . . 12
7. Base64url encoding as used by JWTs . . . . . . . . . . . . . . 14
8. Signing JWTs with Cryptographic Algorithms . . . . . . . . . . 15
8.1. Signing a JWT with HMAC SHA-256 . . . . . . . . . . . . . 15
8.2. Signing a JWT with RSA SHA-256 . . . . . . . . . . . . . . 16
8.3. Signing a JWT with ECDSA P-256 SHA-256 . . . . . . . . . . 17
8.4. Additional Algorithms . . . . . . . . . . . . . . . . . . 19
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
10. Security Considerations . . . . . . . . . . . . . . . . . . . 20
10.1. Unicode Comparison Security Issues . . . . . . . . . . . . 20
11. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 21
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
13. Appendix - Non-Normative - JWT Examples . . . . . . . . . . . 21
13.1. JWT using HMAC SHA-256 . . . . . . . . . . . . . . . . . . 21
13.1.1. Encoding . . . . . . . . . . . . . . . . . . . . . . 21
13.1.2. Decoding . . . . . . . . . . . . . . . . . . . . . . 23
13.1.3. Validating . . . . . . . . . . . . . . . . . . . . . 23
13.2. JWT using RSA SHA-256 . . . . . . . . . . . . . . . . . . 23
13.2.1. Encoding . . . . . . . . . . . . . . . . . . . . . . 23
13.2.2. Decoding . . . . . . . . . . . . . . . . . . . . . . 26
13.2.3. Validating . . . . . . . . . . . . . . . . . . . . . 27
13.3. JWT using ECDSA P-256 SHA-256 . . . . . . . . . . . . . . 27
13.3.1. Encoding . . . . . . . . . . . . . . . . . . . . . . 27
13.3.2. Decoding . . . . . . . . . . . . . . . . . . . . . . 29
13.3.3. Validating . . . . . . . . . . . . . . . . . . . . . 29
14. Appendix - Non-Normative - Notes on implementing base64url
encoding without padding . . . . . . . . . . . . . . . . . . . 29
15. Appendix - Non-Normative - Relationship of JWTs to SAML
Tokens . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
16. Appendix - Non-Normative - Relationship of JWTs to Simple
Web Tokens (SWTs) . . . . . . . . . . . . . . . . . . . . . . 31
17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 31
17.1. Normative References . . . . . . . . . . . . . . . . . . . 31
17.2. Informative References . . . . . . . . . . . . . . . . . . 32
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 33
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1. Introduction
JSON Web Token (JWT) is a simple token format intended for space
constrained environments such as HTTP Authorization headers and URI
query parameters. JWTs encode the claims to be transmitted as a JSON
object (as defined in RFC 4627 [RFC4627]) that is base64url encoded
and digitally signed.
The suggested pronunciation of JWT is the same as the English word
"jot".
2. Terminology
JSON Web Token (JWT) A string consisting of three JWT Token
Segments: the JWT Envelope Segment, the JWT Claim Segment, and the
JWT Crypto Segment, in that order, with the segments being
separated by period ('.') characters.
JWT Token Segment One of the three parts that make up a JSON Web
Token (JWT). JWT Token Segments are always base64url encoded
values.
JWT Envelope Segment A JWT Token Segment containing a base64url
encoded JSON object that describes the signature applied to the
JWT Claim Segment.
JWT Claim Segment A JWT Token Segment containing a base64url encoded
JSON object that encodes the claims represented by the JWT.
JWT Crypto Segment A JWT Token Segment containing base64url encoded
cryptographic signature material that secures the JWT Crypto
Segment's contents.
Decoded JWT Envelope Segment A JWT Envelope Segment that has been
base64url decoded back into a JSON object.
Decoded JWT Claim Segment A JWT Claim Segment that has been
base64url decoded back into a JSON object.
Decoded JWT Crypto Segment A JWT Crypto Segment that has been
base64url decoded back into cryptographic material.
Base64url Encoding For the purposes of this specification, this term
always refers to the he URL- and filename-safe Base64 encoding
described in RFC 4648 [RFC4648], Section 5, with the '=' padding
characters omitted, as permitted by Section 3.2; see Section 7 for
more details.
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3. JSON Web Token (JWT) Overview
JWTs represent a set of claims as a JSON object that is base64url
encoded and digitally signed. 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 JSON object is base64url encoded to produce the JWT Claim
Segment. An accompanying base64url encoded JSON envelope object
describes the signature method used.
The names within the object MUST be unique. The names within the
JSON object are referred to as Claim Names. The corresponding values
are referred to as Claim Values.
JWTs contain a signature that ensures the integrity of the content of
the JSON Claim Segment. This signature value is carried in the JWT
Crypto Segment. The JSON Envelope object MUST contain an "alg"
parameter, the value of which is a string that unambiguously
identifies the algorithm used to sign the JWT Claim Segment to
produce the JWT Crypto Segment.
3.1. Example JWT
The following is an example of a JSON object that can be encoded to
produce a JWT:
{"iss":"joe",
"exp":1300819380,
"http://example.com/is_root":true}
Base64url encoding the UTF-8 representation of the JSON object yields
this JWT Claim Segment value:
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ
The following example JSON envelope object declares that the encoded
object is a JSON Web Token (JWT) and the JWT Claim Segment is signed
using the HMAC SHA-256 algorithm:
{"typ":"JWT",
"alg":"HS256"}
Base64url encoding the UTF-8 representation of the JSON envelope
object yields this JWT Envelope Segment value:
eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
Signing the JWT Claim Segment with the HMAC SHA-256 algorithm and
base64url encoding the result, as per Section 8.1, yields this JWT
Crypto Segment value:
35usWj9X8HwGS-CDcx1JP2NmqcrLwZ4EKp8sNThf3cY
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Combining these segments in the order Envelope.Claims.Signature with
period characters between the segments yields this complete JWT (with
line breaks for display purposes only):
eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ
.
35usWj9X8HwGS-CDcx1JP2NmqcrLwZ4EKp8sNThf3cY
This computation is illustrated in more detail in Section 13.1.
4. JWT Claims
The members of the JSON object represented by the Decoded JWT Claim
Segment contain the claims. Note however, that the set of claims a
JWT must contain to be considered valid is context-dependent and is
outside the scope of this specification.
There are three classes of JWT Claim Names: Reserved Claim Names,
Public Claim Names, and Private Claim Names.
4.1. Reserved Claim Names
The following claim names are reserved. None of the claims defined
in the table below are intended to be mandatory, 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 tokens
themselves to be short.
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+-------+---------+--------------+----------------------------------+
| Claim | JSON | Claim Syntax | Claim Semantics |
| Name | Value | | |
| | Type | | |
+-------+---------+--------------+----------------------------------+
| exp | integer | IntDate | The "exp" (expiration time) |
| | | | claim identifies the expiration |
| | | | time on or after which the token |
| | | | 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. This |
| | | | claim is OPTIONAL. |
| iss | string | StringAndURI | The "iss" (issuer) claim |
| | | | identifies the principal that |
| | | | issued the JWT. The processing |
| | | | of this claim is generally |
| | | | application specific. This |
| | | | claim is OPTIONAL. |
| aud | string | StringAndURI | The "aud" (audience) claim |
| | | | identifies the audience that the |
| | | | JWT is intended for. The |
| | | | processing of this claim |
| | | | requires that if a JWT consumer |
| | | | receives a JWT with an "aud" |
| | | | value that does not identify |
| | | | itself as the JWT audience, then |
| | | | the JWT MUST be rejected. The |
| | | | interpretation of the audience |
| | | | value is generally application |
| | | | specific. This claim is |
| | | | OPTIONAL. |
| typ | string | StringAndURI | The "typ" (type) claim is used |
| | | | to declare a type for the |
| | | | contents this JWT. The value |
| | | | MAY be a MIME [RFC2045] type. |
| | | | This claim is OPTIONAL. |
+-------+---------+--------------+----------------------------------+
Table 1: Reserved Claim Definitions
Additional reserved claim names MAY be defined via the IANA JSON Web
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Token Claims registry, as per Section 9. The syntaxes referred to
above are:
+--------------+----------------------------------------------------+
| Syntax Name | Syntax Definition |
+--------------+----------------------------------------------------+
| StringAndURI | Any string value MAY be used but a value |
| | containing a ":" character MUST be a URI as |
| | defined in RFC 3986 [RFC3986]. |
| URI | A URI as defined in RFC 3986 [RFC3986]. |
| IntDate | The number of seconds from 1970-01-01T0:0:0Z as |
| | measured in UTC until the desired date/time. See |
| | RFC 3339 [RFC3339] for details regarding |
| | date/times in general and UTC in particular. |
+--------------+----------------------------------------------------+
Table 2
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
defined in the IANA JSON Web Token Claims registry or be defined as a
URI that contains a collision resistant namespace. Examples of
collision resistant namespaces include:
o Domain Names,
o Object Identifiers (OIDs) as defined in the ITU-T X 660 and X 670
Recommendation series or
o Universally Unique IDentifier (UUID) as defined in RFC 4122
[RFC4122].
In each case, the definer of the name or value MUST 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 any claim name that is
not a Reserved Name Section 4.1 or a Public Name Section 4.2. Unlike
Public Names, these private names are subject to collision and should
be used with caution.
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5. JWT Envelope
The members of the JSON object represented by the Decoded JWT
Envelope Segment describe the signature applied to the JWT Claim
Segment and optionally additional properties of the JWT.
Implementations MUST understand the entire contents of the envelope;
otherwise, the JWT MUST be rejected for processing.
5.1. Reserved Envelope Parameter Names
The following envelope parameter names are reserved. All the names
are short because a core goal of JWTs is for the tokens themselves to
be short.
+-----------+--------+--------------+-------------------------------+
| Envelope | JSON | Envelope | Envelope Parameter Semantics |
| Parameter | Value | Parameter | |
| Name | Type | Syntax | |
+-----------+--------+--------------+-------------------------------+
| alg | string | StringAndURI | The "alg" (algorithm) |
| | | | envelope parameter identifies |
| | | | the cryptographic algorithm |
| | | | used to secure the JWT. A |
| | | | list of reserved alg values |
| | | | is in Table 4. The |
| | | | processing of the "alg" |
| | | | (algorithm) envelope |
| | | | parameter, if present, |
| | | | requires that the value of |
| | | | the "alg" envelope parameter |
| | | | MUST be one that is both |
| | | | supported and for which there |
| | | | exists a key for use with |
| | | | that algorithm associated |
| | | | with the issuer of the JWT. |
| | | | Note however, that if the |
| | | | "iss" (issuer) claim is not |
| | | | included in the JWT Claim |
| | | | Segment, then the manner in |
| | | | which the issuer is |
| | | | determined is application |
| | | | specific. This envelope |
| | | | parameter is REQUIRED. |
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| typ | string | StringAndURI | The "typ" (type) envelope |
| | | | parameter is used to declare |
| | | | that this data structure is a |
| | | | JWT. If a "typ" parameter is |
| | | | present, its value MUST be |
| | | | "JWT". This envelope |
| | | | parameter is OPTIONAL. |
| | | | (Non-normative note: Other |
| | | | values could be used by other |
| | | | specifications to declare |
| | | | data structures other than |
| | | | JWTs, for instance, encrypted |
| | | | JSON tokens.) |
| keyid | string | String | The "keyid" (key ID) envelope |
| | | | parameter is a hint |
| | | | indicating which specific key |
| | | | owned by the signer should be |
| | | | used to validate the |
| | | | signature. This allows |
| | | | signers to explicitly signal |
| | | | a change of key to |
| | | | recipients. Omitting this |
| | | | parameter is equivalent to |
| | | | setting it to an empty |
| | | | string. The format of this |
| | | | parameter is unspecified. |
| | | | This envelope parameter is |
| | | | OPTIONAL. |
| curi | string | URI | The "curi" (certificates URI) |
| | | | envelope parameter is a URI |
| | | | that points to X.509 public |
| | | | key certificates that can be |
| | | | used to validate the |
| | | | signature. This envelope |
| | | | parameter is OPTIONAL. |
| ctp | string | String | The "ctp" (certificate |
| | | | thumbprint) envelope |
| | | | parameter provides a |
| | | | base64url encoded SHA-1 |
| | | | thumbprint of the DER |
| | | | encoding of a certificate |
| | | | that can be used to validate |
| | | | the signature. This envelope |
| | | | parameter is OPTIONAL. |
+-----------+--------+--------------+-------------------------------+
Table 3: Reserved Envelope Parameter Definitions
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Additional reserved envelope parameter names MAY be defined via the
IANA JSON Web Token Envelope Parameters registry, as per Section 9.
The envelope value syntaxes referred to above are defined in Table 2.
5.2. Public Envelope Parameter Names
Additional envelope parameter names can be defined by those using
JWTs. However, in order to prevent collisions, any new envelope
parameter name or algorithm value SHOULD either be defined in the
IANA JSON Web Token Envelope Parameters registry or be defined as a
URI that contains a collision resistant namespace. In each case, the
definer of the name or value MUST take reasonable precautions to make
sure they are in control of the part of the namespace they use to
define the envelope parameter name.
New envelope parameters should be introduced sparingly, as they can
result in non-interoperable JWTs. Nonetheless, some extensions
needed for some use cases may require them, such as an extension to
enable the inclusion of multiple signatures.
5.3. Private Envelope Parameter Names
A producer and consumer of a JWT may agree to any envelope parameter
name that is not a Reserved Name Section 5.1 or a Public Name
Section 5.2. Unlike Public Names, these private names are subject to
collision and should be used with caution.
New envelope parameters should be introduced sparingly, as they can
result in non-interoperable JWTs.
6. General Rules for Creating and Validating a JWT
To create a JWT one MUST follow these steps:
1. Create a JSON object containing the desired claims. Note that
white space is explicitly allowed in the representation and no
canonicalization is performed before encoding.
2. Translate this JSON object's Unicode code points into UTF-8, as
defined in RFC 3629 [RFC3629].
3. Base64url encode the UTF-8 representation of this JSON object as
defined in this specification (without padding). This encoding
becomes the JWT Claim Segment.
4. Create a different JSON object containing the desired envelope
parameters. Note that white space is explicitly allowed in the
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representation and no canonicalization is performed before
encoding.
5. Translate this JSON object's Unicode code points into UTF-8, as
defined in RFC 3629 [RFC3629].
6. Base64url encode the UTF-8 representation of this JSON object as
defined in this specification (without padding). This encoding
becomes the JWT Envelope Segment.
7. Construct the JWT Crypto Segment as defined for the particular
algorithm being used. The "alg" envelope parameter MUST be
present in the JSON Envelope Segment, with the algorithm value
accurately representing the algorithm used to construct the JWT
Crypto Segment.
8. Combine the JWT Envelope Segment, the JWT Claim Segment and then
the JWT Crypto Segment in that order, separating each by period
characters, to create the JWT.
When validating a JWT the following steps MUST be taken. If any of
the listed steps fails then the token MUST be rejected for
processing.
1. The JWT MUST contain two period characters.
2. The JWT MUST be split on the two period characters resulting in
three non-empty segments. The first segment is the JWT Envelope
Segment; the second is the JWT Claim Segment; the third is the
JWT Crypto Segment.
3. The JWT Envelope Segment MUST be successfully base64url decoded
following the restriction given in this spec that no padding
characters may have been used.
4. The Decoded JWT Envelope Segment MUST be completely valid JSON
syntax.
5. The JWT Claim Segment MUST be successfully base64url decoded
following the restriction given in this spec that no padding
characters may have been used.
6. The Decoded JWT Claim Segment MUST be completely valid JSON
syntax.
7. The JWT Crypto Segment MUST be successfully base64url decoded
following the restriction given in this spec that no padding
characters may have been used.
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8. The JWT Envelope Segment MUST be validated to only include
parameters and values whose syntax and semantics are both
understood and supported.
9. When used in a security-related context, the JWT Claim Segment
MUST be validated to only include claims whose syntax and
semantics are both understood and supported.
10. The JWT Crypto Segment MUST be successfully validated against
the JWT Claim Segment in the manner defined for the algorithm
being used, which MUST be accurately represented by the value of
the "alg" envelope parameter, which MUST be present.
Processing a JWT inevitably requires comparing known strings to
values in the token. For example, in checking what the algorithm is,
the Unicode string encoding "alg" will be checked against the member
names in the Decoded JWT Envelope Segment to see if there is a
matching envelope parameter name. A similar process occurs when
determining if the value of the "alg" envelope parameter represents a
supported algorithm. Comparing Unicode strings, however, has
significant security implications, as per Section 10.
Comparisons between JSON strings and other Unicode strings MUST be
performed as specified below:
1. Remove any JSON applied escaping to produce an array of Unicode
code points.
2. Unicode Normalization [USA15] MUST NOT be applied at any point to
either the JSON string or to the string it is to be compared
against.
3. Comparisons between the two strings MUST be performed as a
Unicode code point to code point equality comparison.
7. Base64url encoding as used by JWTs
JWTs make use of the base64url encoding as defined in RFC 4648
[RFC4648]. As allowed by Section 3.2 of the RFC, this specification
mandates that base64url encoding when used with JWTs MUST NOT use
padding. The reason for this restriction is that the padding
character ('=') is not URL safe.
For notes on implementing base64url encoding without padding, see
Section 14.
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8. Signing JWTs with Cryptographic Algorithms
JWTs use specific cryptographic algorithms to sign the contents of
the JWT Claim Segment. The use of the following algorithms for
producing JWTs is defined in this section. The table below is the
list of "alg" envelope parameter values reserved by this
specification, each of which is explained in more detail in the
following sections:
+-----------------+-------------------------------------------------+
| Alg Claim Value | Algorithm |
+-----------------+-------------------------------------------------+
| HS256 | HMAC using SHA-256 hash algorithm |
| HS384 | HMAC using SHA-384 hash algorithm |
| HS512 | HMAC using SHA-512 hash algorithm |
| RS256 | RSA using SHA-256 hash algorithm |
| RS384 | RSA using SHA-384 hash algorithm |
| RS512 | RSA using SHA-512 hash algorithm |
| ES256 | ECDSA using P-256 curve and SHA-256 hash |
| | algorithm |
| ES384 | ECDSA using P-384 curve and SHA-384 hash |
| | algorithm |
| ES512 | ECDSA using P-521 curve and SHA-512 hash |
| | algorithm |
+-----------------+-------------------------------------------------+
Table 4: JSON Web Token Reserved Algorithm Values
Of these algorithms, only HMAC SHA-256 and RSA SHA-256 MUST be
implemented. It is RECOMMENDED that implementations also implement
at least the ECDSA P-256 SHA-256 algorithm.
8.1. Signing a JWT with HMAC SHA-256
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 JWT Claim Segment,
which therefore demonstrates that whoever generated the MAC was in
possession of the secret.
The algorithm for implementing and validating HMACs is provided in
RFC 2104 [RFC2104]. Although any HMAC can be used with JWTs, this
section defines the use of the SHA-256 cryptographic hash function as
defined in FIPS 180-3 [FIPS.180-3]. The reserved "alg" envelope
parameter value "HS256" is used in the JWT Envelope Segment to
indicate that the JWT Crypto Segment contains a base64url encoded
HMAC SHA-256 HMAC value.
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The HMAC SHA-256 MAC is generated as follows:
1. Take the bytes of the UTF-8 representation of the JWT Claim
Segment and execute the HMAC SHA-256 algorithm on them using the
shared key to produce an HMAC.
2. Base64url encode the HMAC as defined in this document.
The output is placed in the JWT Crypto Segment for that JWT.
The HMAC SHA-256 MAC on a JWT is validated as follows:
1. Take the bytes of the UTF-8 representation of the JWT Claim
Segment and calculate an HMAC SHA-256 MAC on them using the
shared key.
2. Base64url encode the previously generated HMAC as defined in this
document.
3. If the JWT Crypto Segment and the previously calculated value
exactly match in a character by character, case sensitive
comparison, then one has confirmation that the key was used to
generate the HMAC on the JWT and that the contents of the JWT
Claim Segment have not be tampered with.
4. If the validation fails, the token MUST be rejected.
Signing with the HMAC SHA-384 and HMAC SHA-512 algorithms is
performed identically to the procedure for HMAC SHA-256 - just with
correspondingly longer key and result values.
JWT implementations MUST support the HMAC SHA-256 algorithm. Support
for the HMAC SHA-384 and HMAC SHA-512 algorithms is OPTIONAL.
8.2. Signing a JWT with RSA SHA-256
This section defines the use of the RSASSA-PKCS1-v1_5 signature
algorithm as defined in RFC 3447 [RFC3447], Section 8.2 (commonly
known as PKCS#1), using SHA-256 as the hash function. Note that the
use of the RSASSA-PKCS1-v1_5 algorithm is permitted in FIPS 186-3
[FIPS.186-3], Section 5.5, as is the SHA-256 cryptographic hash
function, which is defined in FIPS 180-3 [FIPS.180-3]. The reserved
"alg" envelope parameter value "RS256" is used in the JWT Envelope
Segment to indicate that the JWT Crypto Segment contains an RSA SHA-
256 signature.
A 2048-bit or longer key length MUST be used with this algorithm.
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The RSA SHA-256 signature is generated as follows:
1. Let K be the signer's RSA private key and let M be the bytes of
the UTF-8 representation of the JWT Claim Segment.
2. Compute the octet string S = RSASSA-PKCS1-V1_5-SIGN (K, M).
3. Base64url encode the octet string S, as defined in this document.
The output is placed in the JWT Crypto Segment for that JWT.
The RSA SHA-256 signature on a JWT is validated as follows:
1. Take the JWT Crypto Segment and base64url decode it into an octet
string S. If decoding fails, then the token MUST be rejected.
2. Let M be the bytes of the UTF-8 representation of the JWT Claim
Segment and let (n, e) be the public key corresponding to the
private key used by the signer.
3. Validate the signature with RSASSA-PKCS1-V1_5-VERIFY ((n, e), M,
S).
4. If the validation fails, the token 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 longer key and result values.
JWT implementations MUST support the RSA SHA-256 algorithm. Support
for the RSA SHA-384 and RSA SHA-512 algorithms is OPTIONAL.
8.3. Signing a JWT with ECDSA P-256 SHA-256
The Elliptic Curve Digital Signature Algorithm (ECDSA) is defined by
FIPS 186-3 [FIPS.186-3]. ECDSA provides for the use of Elliptic
Curve cryptography, which is able to provide equivalent security to
RSA cryptography but using shorter key lengths and with greater
processing speed. This means that ECDSA 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. The P-256 curve is also
defined in FIPS 186-3. The reserved "alg" envelope parameter value
"ES256" is used in the JWT Envelope Segment to indicate that the JWT
Crypto Segment contains a ECDSA P-256 SHA-256 signature.
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A JWT is signed with an ECDSA P-256 SHA-256 signature as follows:
1. Take the bytes of the UTF-8 representation of the JWT Claim
Segment and generate a digital signature of them 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 64 byte array as defined in this
specification.
The output becomes the JWT Crypto Segment for the JWT.
The following procedure is used to validate the ECDSA signature of a
JWT:
1. Take the JWT Crypto Segment and base64url decode it into a byte
array. If decoding fails, the token 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. Remember that the byte arrays are in
big endian byte order; please check the ECDSA validator in use to
see what byte order it requires.
4. Submit the bytes of the UTF-8 representation of the JWT Claim
Segment, R, S and the public key (x, y) to the ECDSA P-256 SHA-
256 validator.
5. If the validation fails, the token 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 signatures because their K values will be different. The
consequence of this is that one must validate an ECDSA 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 longer key and result values.
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It is RECOMMENDED that JWT implementations support the ECDSA P-256
SHA-256 algorithm. Support for the ECDSA P-384 SHA-384 and ECDSA
P-521 SHA-512 algorithms is OPTIONAL.
8.4. Additional Algorithms
Additional algorithms MAY be used to protect JWTs with corresponding
"alg" envelope parameter values being defined to refer to them. Like
claim names, new "alg" envelope parameter values SHOULD either be
defined in the IANA JSON Web Token Algorithms registry or be a URI
that contains a collision resistant namespace. In particular, the
use of algorithm identifiers defined in XML DSIG [RFC3275] and
related specifications is permitted.
9. IANA Considerations
This specification calls for:
o A new IANA registry entitled "JSON Web Token Claims" for reserved
claim names Section 4.1 used in a Decoded JWT Claim Segment.
Inclusion in the registry is RFC Required in the RFC 5226
[RFC5226] sense for reserved JWT claim names that are intended to
be interoperable between implementations. The registry will just
record the reserved claim name and a pointer to the RFC that
defines it. This specification defines inclusion of the claim
names defined in Table 1.
o A new IANA registry entitled "JSON Web Token Envelope Parameters"
for reserved envelope parameter names Section 5.1 used in a
Decoded JWT Envelope Parameter Segment. Inclusion in the registry
is RFC Required in the RFC 5226 [RFC5226] sense for reserved JWT
envelope parameter names that are intended to be interoperable
between implementations. The registry will just record the
reserved envelope parameter name and a pointer to the RFC that
defines it. This specification defines inclusion of the envelope
parameter names defined in Table 3.
o A new IANA registry entitled "JSON Web Token Algorithms" for
reserved values used with the "alg" envelope parameter values used
in a decoded JWT Envelope Segment. Inclusion in the registry is
RFC Required in the RFC 5226 [RFC5226] sense. The registry will
just record the "alg" value and a pointer to the RFC that defines
it. This specification defines inclusion of the algorithm values
defined in Table 4.
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10. Security Considerations
TBD: Lots of work to do here. We need to remember to look into any
issues relating to security and JSON parsing. One wonders just how
secure most JSON parsing libraries are. Were they ever hardened for
security scenarios? If not, what kind of holes does that open up?
Also, we need to walk through the JSON standard and see what kind of
issues we have especially around comparison of names. For instance,
comparisons of claim names and other parameters must occur after they
are unescaped. Need to also put in text about: Importance of keeping
secrets secret. Rotating keys. Strengths and weaknesses of the
different algorithms. Case sensitivity and more generally Unicode
comparison issues that can cause security holes, especially in claim
names and explain why Unicode Normalization is such a problem.
TBD: Need to put in text about why strict JSON validation is
necessary. Basically, that if malformed JSON is received then the
intent of the sender is impossible to reliably discern. While in
non-security contexts it's o.k. to be generous in what one accepts,
in security contexts this can lead to serious security holes. For
example, malformed JSON might indicate that someone has managed to
find a security hole in the issuer's code and is leveraging it to get
the issuer to issue "bad" tokens whose content the attacker can
control.
10.1. Unicode Comparison Security Issues
Claim names in JWTs are Unicode strings. For security reasons, the
representations these names must be compared verbatim after
performing any escape processing (as per RFC 4627 [RFC4627], Section
2.5). In particular, Unicode Normalization [USA15] or case folding
MUST NOT be applied at any point to either the JSON string or to the
string it is to be compared against.
This means, for instance, that these JSON strings must compare as
being equal ("JWT", "\u004aWT"), whereas these must all compare as
being not equal to the first set or to each other ("jwt", "Jwt",
"JW\u0074").
JSON strings MAY contain characters outside the Unicode Basic
Multilingual Plane. For instance, the G clef character (U+1D11E) may
be represented in a JSON string as "\uD834\uDD1E". Ideally, JWT
implementations SHOULD ensure that characters outside the Basic
Multilingual Plane are preserved and compared correctly;
alternatively, if this is not possible due to these characters
exercising limitations present in the underlying JSON implementation,
then input containing them MUST be rejected.
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11. Open Issues
The following open issues have been identified during review of
previous drafts. Additional input on them is solicited.
o The draft currently defines no mechanism(s) for retrieving public
keys that are not encoded as X.509 certificates. A mechanism or
mechanisms similar to the Magic Signatures key discovery process
for Magic Keys could be added to future drafts. Some have
suggested that they keys themselves also be encoded as JWTs.
o Related to the above, it's not clear whether the "iss" claim
should be expected to contain a location for retrieving non-X.509
public keys, or whether a separate issuer key location parameter
should be defined. Also, does this belong in the envelope or the
claims?
12. Acknowledgements
The authors acknowledge that the design of JWTs was intentionally
influenced by the design and simplicity of Simple Web Tokens [SWT].
Solutions for signing JSON tokens were also previously explored by
Magic Signatures [MagicSignatures], JSON Simple Sign [JSS], and
Canvas Applications [CanvasApp], all of which influenced this draft.
13. Appendix - Non-Normative - JWT Examples
13.1. JWT using HMAC SHA-256
13.1.1. Encoding
The Decoded JWT Claim Segment used in this example is:
{"iss":"joe",
"exp":1300819380,
"http://example.com/is_root":true}
Note that white space is explicitly allowed in Decoded JWT Claim
Segments and no canonicalization is performed before encoding. The
following byte array contains the UTF-8 characters for the Decoded
JWT Claim Segment:
[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]
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Base64url encoding the above yields the JWT Claim Segment value:
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ
The following example JSON envelope object declares that the encoded
object is a JSON Web Token (JWT) and the JWT Claim Segment is signed
using the HMAC SHA-256 algorithm:
{"typ":"JWT",
"alg":"HS256"}
The following byte array contains the UTF-8 characters for the
Decoded JWT Envelope Segment:
[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 this UTF-8 representation yields this JWT Envelope
Segment value:
eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
HMACs are generated using keys. This example used the key
represented by the following byte array:
[83, 159, 117, 12, 235, 169, 168, 200, 131, 152, 227, 246, 214, 212,
188, 74, 71, 83, 244, 166, 90, 24, 239, 251, 32, 124, 6, 201, 194,
104, 241, 62, 174, 246, 65, 111, 49, 52, 210, 118, 212, 124, 34, 88,
167, 112, 84, 88, 83, 65, 155, 18, 234, 250, 224, 101, 147, 221, 23,
104, 219, 170, 146, 215]
Running the HMAC SHA-256 algorithm on the JWT Claim Segment with this
key yields the following byte array:
[223, 155, 172, 90, 63, 87, 240, 124, 6, 75, 224, 131, 115, 29, 73,
63, 99, 102, 169, 202, 203, 193, 158, 4, 42, 159, 44, 53, 56, 95,
221, 198]
Base64url encoding the above HMAC output yields the JWT Crypto
Segment value:
35usWj9X8HwGS-CDcx1JP2NmqcrLwZ4EKp8sNThf3cY
Combining these segments in the order Envelope.Claims.Signature with
period characters between the segments yields this complete JWT (with
line breaks for display purposes only):
eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ
.
35usWj9X8HwGS-CDcx1JP2NmqcrLwZ4EKp8sNThf3cY
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13.1.2. Decoding
Decoding the JWT first requires removing the base64url encoding from
the JWT Envelope Segment and the JWT Claim Segment. We base64url
decode the segments per Section 7 and turn them into the
corresponding UTF-8 byte arrays, which we then translate into the
Decoded JWT Envelope Segment and Decoded JWT Claim Segment strings.
13.1.3. Validating
Next we validate the decoded results. Since the "alg" parameter in
the envelope is "HS256", we validate the HMAC SHA-256 signature
contained in the JWT Crypto Segment. If any of the validation steps
fail, the token MUST be rejected.
First, we validate that the decoded envelope and claim segment
strings are both legal JSON.
To validate the signature, we repeat the previous process of using
the correct key and the JWT Claim Segment as input to a SHA-256 HMAC
function and then taking the output, base64url encoding it, and
determining if it matches the JWT Crypto Segment in the JWT. If it
matches exactly, the token has been validated.
13.2. JWT using RSA SHA-256
13.2.1. Encoding
The Decoded JWT Claim Segment used in this example is the same as in
the previous example:
{"iss":"joe",
"exp":1300819380,
"http://example.com/is_root":true}
Since the JWT Claim Segment will therefore be the same, its
computation is not repeated here. However, the Decoded JWT Envelope
Segment is different in two ways: First, because a different
algorithm is being used, the "alg" value is different. Second, for
illustration purposes only, the optional "typ" parameter is not used.
(This difference is not related to the signature algorithm employed.)
The Decoded JWT Envelope Segment used is:
{"alg":"RS256"}
The following byte array contains the UTF-8 characters for the
Decoded JWT Envelope Segment:
[123, 34, 97, 108, 103, 34, 58, 34, 82, 83, 50, 53, 54, 34, 125]
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Base64url encoding this UTF-8 representation yields this JWT Envelope
Segment value:
eyJhbGciOiJSUzI1NiJ9
The RSA key consists of a public part (n, e), and a private exponent
d. The values of the RSA key used in this example, presented as the
byte arrays representing big endian integers are:
+-----------+-------------------------------------------------------+
| Parameter | Value |
| Name | |
+-----------+-------------------------------------------------------+
| n | [210, 252, 123, 106, 10, 30, 108, 103, 16, 74, 235, |
| | 143, 136, 178, 87, 102, 155, 77, 246, 121, 221, 173, |
| | 9, 155, 92, 74, 108, 217, 168, 128, 21, 181, 161, 51, |
| | 191, 11, 133, 108, 120, 113, 182, 223, 0, 11, 85, 79, |
| | 206, 179, 194, 237, 81, 43, 182, 143, 20, 92, 110, |
| | 132, 52, 117, 47, 171, 82, 161, 207, 193, 36, 64, |
| | 143, 121, 181, 138, 69, 120, 193, 100, 40, 133, 87, |
| | 137, 247, 162, 73, 227, 132, 203, 45, 159, 174, 45, |
| | 103, 253, 150, 251, 146, 108, 25, 142, 7, 115, 153, |
| | 253, 200, 21, 192, 175, 9, 125, 222, 90, 173, 239, |
| | 244, 77, 231, 14, 130, 127, 72, 120, 67, 36, 57, 191, |
| | 238, 185, 96, 104, 208, 71, 79, 197, 13, 109, 144, |
| | 191, 58, 152, 223, 175, 16, 64, 200, 156, 2, 214, |
| | 146, 171, 59, 60, 40, 150, 96, 157, 134, 253, 115, |
| | 183, 116, 206, 7, 64, 100, 124, 238, 234, 163, 16, |
| | 189, 18, 249, 133, 168, 235, 159, 89, 253, 212, 38, |
| | 206, 165, 178, 18, 15, 79, 42, 52, 188, 171, 118, 75, |
| | 126, 108, 84, 214, 132, 2, 56, 188, 196, 5, 135, 165, |
| | 158, 102, 237, 31, 51, 137, 69, 119, 99, 92, 71, 10, |
| | 247, 92, 249, 44, 32, 209, 218, 67, 225, 191, 196, |
| | 25, 226, 34, 166, 240, 208, 187, 53, 140, 94, 56, |
| | 249, 203, 5, 10, 234, 254, 144, 72, 20, 241, 172, 26, |
| | 164, 156, 202, 158, 160, 202, 131] |
| e | [1, 0, 1] |
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| d | [95, 135, 19, 181, 226, 88, 254, 9, 248, 21, 131, |
| | 236, 92, 31, 43, 117, 120, 177, 230, 252, 44, 131, |
| | 81, 75, 55, 145, 55, 17, 161, 186, 68, 154, 21, 31, |
| | 225, 203, 44, 160, 253, 51, 183, 113, 230, 138, 59, |
| | 25, 68, 100, 157, 200, 103, 173, 28, 30, 82, 64, 187, |
| | 133, 62, 95, 36, 179, 52, 89, 177, 64, 40, 210, 214, |
| | 99, 107, 239, 236, 30, 141, 169, 116, 179, 82, 252, |
| | 83, 211, 246, 18, 126, 168, 163, 194, 157, 209, 79, |
| | 57, 65, 104, 44, 86, 167, 135, 104, 22, 78, 77, 218, |
| | 143, 6, 203, 249, 199, 52, 170, 232, 0, 50, 36, 39, |
| | 142, 169, 69, 74, 33, 177, 124, 176, 109, 23, 128, |
| | 117, 134, 140, 192, 91, 61, 182, 255, 29, 253, 195, |
| | 213, 99, 120, 180, 237, 173, 237, 240, 195, 122, 76, |
| | 220, 38, 209, 212, 154, 194, 111, 111, 227, 181, 34, |
| | 10, 93, 210, 147, 150, 98, 27, 188, 104, 140, 242, |
| | 238, 226, 198, 224, 213, 77, 163, 199, 130, 1, 76, |
| | 208, 115, 157, 178, 82, 204, 81, 202, 235, 168, 211, |
| | 241, 184, 36, 186, 171, 36, 208, 104, 236, 144, 50, |
| | 100, 215, 214, 120, 171, 8, 240, 110, 201, 231, 226, |
| | 61, 150, 6, 40, 183, 68, 191, 148, 179, 105, 70, 86, |
| | 70, 60, 126, 65, 115, 153, 237, 115, 208, 118, 200, |
| | 145, 252, 244, 99, 169, 170, 156, 230, 45, 169, 205, |
| | 23, 226, 55, 220, 42, 128, 2, 241] |
+-----------+-------------------------------------------------------+
The RSA private key (n, d) is then passed to the RSA signing
function, which also takes the hash type, SHA-256, and the JWT Claim
Segment as inputs. The result of the signature is a byte array S,
which represents a big endian integer. In this example, S is:
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+--------+----------------------------------------------------------+
| Result | Value |
| Name | |
+--------+----------------------------------------------------------+
| S | [208, 141, 219, 44, 66, 129, 179, 230, 69, 120, 123, |
| | 108, 203, 96, 182, 145, 66, 179, 198, 104, 43, 187, 199, |
| | 159, 175, 5, 217, 101, 109, 236, 88, 136, 193, 133, 79, |
| | 39, 162, 131, 58, 114, 133, 202, 171, 227, 135, 157, |
| | 123, 188, 90, 111, 66, 241, 38, 238, 59, 18, 125, 146, |
| | 129, 14, 54, 183, 10, 221, 33, 105, 37, 173, 119, 239, |
| | 92, 27, 232, 175, 173, 49, 21, 28, 252, 237, 183, 107, |
| | 98, 156, 113, 116, 162, 219, 53, 96, 44, 214, 175, 154, |
| | 61, 100, 175, 90, 118, 247, 42, 196, 45, 74, 217, 145, |
| | 92, 39, 123, 224, 247, 171, 206, 203, 91, 167, 103, 57, |
| | 163, 87, 172, 67, 77, 255, 9, 218, 107, 62, 228, 71, |
| | 239, 36, 246, 23, 96, 108, 28, 19, 179, 24, 167, 196, |
| | 42, 97, 198, 80, 241, 79, 31, 0, 85, 17, 50, 6, 143, |
| | 238, 214, 131, 246, 13, 49, 111, 30, 142, 182, 145, 200, |
| | 17, 127, 76, 236, 69, 66, 133, 198, 137, 103, 45, 3, 48, |
| | 123, 203, 17, 162, 1, 105, 133, 22, 105, 25, 63, 173, |
| | 186, 231, 206, 246, 22, 243, 250, 53, 237, 209, 36, 111, |
| | 168, 11, 40, 237, 179, 83, 125, 180, 84, 231, 129, 37, |
| | 236, 172, 22, 234, 58, 198, 187, 124, 65, 145, 148, 227, |
| | 122, 177, 16, 176, 84, 28, 1, 141, 179, 57, 96, 232, |
| | 215, 51, 7, 49, 63, 195, 155, 94, 51, 22, 239, 90, 138, |
| | 207, 41, 62] |
+--------+----------------------------------------------------------+
Base64url encoding the signature produces this value for the JWT
Crypto Segment:
0I3bLEKBs-ZFeHtsy2C2kUKzxmgru8efrwXZZW3sWIjBhU8nooM6coXKq-OHnXu8Wm9C8SbuOxJ9koEONrcK3SFpJa1371wb6K-tMRUc_O23a2KccXSi2zVgLNavmj1kr1p29yrELUrZkVwne-D3q87LW6dnOaNXrENN_wnaaz7kR-8k9hdgbBwTsxinxCphxlDxTx8AVREyBo_u1oP2DTFvHo62kcgRf0zsRUKFxolnLQMwe8sRogFphRZpGT-tuufO9hbz-jXt0SRvqAso7bNTfbRU54El7KwW6jrGu3xBkZTjerEQsFQcAY2zOWDo1zMHMT_Dm14zFu9ais8pPg
Combining these segments in the order Envelope.Claims.Signature with
period characters between the segments yields this complete JWT (with
line breaks for display purposes only):
eyJhbGciOiJSUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ
.
0I3bLEKBs-ZFeHtsy2C2kUKzxmgru8efrwXZZW3sWIjBhU8nooM6coXKq-OHnXu8Wm9C8SbuOxJ9koEONrcK3SFpJa1371wb6K-tMRUc_O23a2KccXSi2zVgLNavmj1kr1p29yrELUrZkVwne-D3q87LW6dnOaNXrENN_wnaaz7kR-8k9hdgbBwTsxinxCphxlDxTx8AVREyBo_u1oP2DTFvHo62kcgRf0zsRUKFxolnLQMwe8sRogFphRZpGT-tuufO9hbz-jXt0SRvqAso7bNTfbRU54El7KwW6jrGu3xBkZTjerEQsFQcAY2zOWDo1zMHMT_Dm14zFu9ais8pPg
13.2.2. Decoding
Decoding the JWT from this example requires processing the JWT
Envelope Segment and Claim Segment exactly as done in the first
example.
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13.2.3. Validating
Since the "alg" parameter in the envelope is "RS256", we validate the
RSA SHA-256 signature contained in the JWT Crypto Segment. If any of
the validation steps fail, the token MUST be rejected.
First, we validate that the decoded envelope and claim segment
strings are both legal JSON.
Validating the JWT Crypto Segment is a little different from the
previous example. First, we base64url decode the JWT Crypto Segment
to produce a signature S to check. We then pass (n, e), S and the
JWT Claim Segment to an RSA signature verifier that has been
configured to use the SHA-256 hash function.
13.3. JWT using ECDSA P-256 SHA-256
13.3.1. Encoding
The Decoded JWT Claim Segment used in this example is the same as in
the previous examples:
{"iss":"joe",
"exp":1300819380,
"http://example.com/is_root":true}
Since the JWT Claim Segment will therefore be the same, its
computation is not repeated here. However, the Decoded JWT Envelope
Segment is differs from the previous example because a different
algorithm is being used. The Decoded JWT Envelope Segment used is:
{"alg":"ES256"}
The following byte array contains the UTF-8 characters for the
Decoded JWT Envelope Segment:
[123, 34, 97, 108, 103, 34, 58, 34, 69, 83, 50, 53, 54, 34, 125]
Base64url encoding this UTF-8 representation yields this JWT Envelope
Segment value:
eyJhbGciOiJFUzI1NiJ9
The ECDSA key consists of a public part, the EC point (x, y), and a
private part d. The values of the ECDSA key used in this example,
presented as the byte arrays representing big endian integers are:
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+-----------+-------------------------------------------------------+
| Parameter | Value |
| Name | |
+-----------+-------------------------------------------------------+
| x | [48, 160, 66, 76, 210, 28, 41, 68, 131, 138, 45, 117, |
| | 201, 43, 55, 231, 110, 162, 13, 159, 0, 137, 58, 59, |
| | 78, 238, 138, 60, 10, 175, 236, 62] |
| y | [224, 75, 101, 233, 36, 86, 217, 136, 139, 82, 179, |
| | 121, 189, 251, 213, 30, 232, 105, 239, 31, 15, 198, |
| | 91, 102, 89, 105, 91, 108, 206, 8, 23, 35] |
| d | [243, 189, 12, 7, 168, 31, 185, 50, 120, 30, 213, 39, |
| | 82, 246, 12, 200, 154, 107, 229, 229, 25, 52, 254, 1, |
| | 147, 141, 219, 85, 216, 247, 120, 1] |
+-----------+-------------------------------------------------------+
The ECDSA private part d is then passed to an ECDSA signing function,
which also takes the curve type, P-256, the hash type, SHA-256, and
the JWT Claim Segment as inputs. The result of the signature is the
EC point (R, S), where R and S are unsigned integers. In this
example, the R and S values, given as byte arrays representing big
endian integers are:
+--------+----------------------------------------------------------+
| Result | Value |
| Name | |
+--------+----------------------------------------------------------+
| R | [175, 11, 115, 42, 160, 182, 181, 28, 135, 222, 52, 154, |
| | 182, 237, 206, 137, 82, 20, 243, 7, 12, 164, 107, 72, |
| | 236, 187, 241, 190, 26, 76, 32, 181] |
| S | [120, 23, 189, 205, 202, 13, 177, 187, 23, 47, 12, 227, |
| | 237, 250, 230, 233, 245, 216, 9, 170, 24, 185, 198, 187, |
| | 193, 94, 158, 117, 167, 88, 153, 196] |
+--------+----------------------------------------------------------+
Concatenating the S array to the end of the R array and base64url
encoding the result produces this value for the JWT Crypto Segment:
rwtzKqC2tRyH3jSatu3OiVIU8wcMpGtI7LvxvhpMILV4F73Nyg2xuxcvDOPt-ubp9dgJqhi5xrvBXp51p1iZxA
Combining these segments in the order Envelope.Claims.Signature with
period characters between the segments yields this complete JWT (with
line breaks for display purposes only):
eyJhbGciOiJFUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ
.
rwtzKqC2tRyH3jSatu3OiVIU8wcMpGtI7LvxvhpMILV4F73Nyg2xuxcvDOPt-ubp9dgJqhi5xrvBXp51p1iZxA
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13.3.2. Decoding
Decoding the JWT from this example requires processing the JWT
Envelope Segment and Claim Segment exactly as done in the first
example.
13.3.3. Validating
Since the "alg" parameter in the envelope is "ES256", we validate the
ECDSA P-256 SHA-256 signature contained in the JWT Crypto Segment.
If any of the validation steps fail, the token MUST be rejected.
First, we validate that the decoded envelope and claim segment
strings are both legal JSON.
Validating the JWT Crypto Segment is a little different from the
first example. First, we base64url decode the JWT Crypto Segment as
in the previous examples but we then need to split the 64 member byte
array that must result into two 32 byte arrays, the first R and the
second S. We then pass (x, y), (R, S) and the JWT Claim Segment to an
ECDSA signature verifier that has been configured to use the P-256
curve with the SHA-256 hash function.
As explained in Section 8.3, the use of the k value in ECDSA means
that we cannot validate the correctness of the signature in the same
way we validated the correctness of the HMAC. Instead,
implementations MUST use an ECDSA validator to validate the
signature.
14. Appendix - Non-Normative - Notes on implementing base64url encoding
without padding
This appendix describes how to implement base64url encoding and
decoding functions without padding based upon standard base64
encoding and decoding functions that do use padding.
To be concrete, example C# code implementing these functions is shown
below. Similar code could be used in other languages.
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static string base64urlencode(byte [] arg)
{
string s = Convert.ToBase64String(arg); // Standard base64 encoder
s = s.Split('=')[0]; // Remove any trailing '='s
s = s.Replace('+', '-'); // 62nd char of encoding
s = s.Replace('/', '_'); // 63rd char of encoding
return s;
}
static byte [] base64urldecode(string arg)
{
string s = arg;
s = s.Replace('-', '+'); // 62nd char of encoding
s = s.Replace('_', '/'); // 63rd char of encoding
switch (s.Length % 4) // Pad with trailing '='s
{
case 0: break; // No pad chars in this case
case 2: s += "=="; break; // Two pad chars
case 3: s += "="; break; // One pad char
default: throw new System.Exception(
"Illegal base64url string!");
}
return Convert.FromBase64String(s); // Standard base64 decoder
}
As per the example code above, the number of '=' padding characters
that needs to be added to the end of a base64url encoded string
without padding to turn it into one with padding is a deterministic
function of the length of the encoded string. Specifically, if the
length mod 4 is 0, no padding is added; if the length mod 4 is 2, two
'=' padding characters are added; if the length mod 4 is 3, one '='
padding character is added; if the length mod 4 is 1, the input is
malformed.
An example correspondence between unencoded and encoded values
follows. The byte sequence below encodes into the string below,
which when decoded, reproduces the byte sequence.
3 236 255 224 193
A-z_4ME
15. Appendix - Non-Normative - Relationship of JWTs to SAML Tokens
SAML 2.0 [OASIS.saml-core-2.0-os] provides a standard for creating
tokens with much greater expressivity and more security options than
supported by JWTs. However, the cost of this flexibility and
expressiveness is both size and complexity. In addition, SAML's use
of XML [W3C.CR-xml11-20021015] and XML DSIG [RFC3275] only
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contributes to the size of SAML tokens.
JWTs are intended to provide a simple 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 Hash-based Message Authentication Codes (HMACs) and
digital signatures using a smaller (and less flexible) format than
XML DSIG.
Therefore, while JWTs can do some of the things SAML tokens do, JWTs
are not intended as a full replacement for SAML tokens, but rather as
a compromise token format to be used when space is at a premium.
16. Appendix - Non-Normative - 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 HMAC SHA-256,
RSA SHA-256, and ECDSA P-256 SHA-256.
17. References
17.1. Normative References
[FIPS.180-3]
National Institute of Standards and Technology, "Secure
Hash Standard (SHS)", FIPS PUB 180-3, October 2008.
[FIPS.186-3]
National Institute of Standards and Technology, "Digital
Signature Standard (DSS)", FIPS PUB 186-3, June 2009.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
February 1997.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
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Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3339] Klyne, G., Ed. and C. Newman, "Date and Time on the
Internet: Timestamps", RFC 3339, July 2002.
[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications
Version 2.1", RFC 3447, February 2003.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[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.
[USA15] Davis, M., Whistler, K., and M. Duerst, "Unicode
Normalization Forms", Unicode Standard Annex 15, 09 2009.
17.2. 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", August 2010.
[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
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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.
Authors' Addresses
Michael B. Jones
Microsoft
Email: mbj@microsoft.com
URI: http://self-issued.info/
Dirk Balfanz
Google
Email: balfanz@google.com
John Bradley
independent
Email: ve7jtb@ve7jtb.com
Yaron Y. Goland
Microsoft
Email: yarong@microsoft.com
John Panzer
Google
Email: jpanzer@google.com
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Nat Sakimura
Nomura Research Institute
Email: n-sakimura@nri.co.jp
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