JSON Web Signature (JWS)
draft-ietf-jose-json-web-signature-32

Abstract

JSON Web Signature (JWS) represents content secured with digital signatures or Message Authentication Codes (MACs) using JavaScript Object Notation (JSON) based data structures. Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) specification and an IANA registry defined by that specification. Related encryption capabilities are described in the separate JSON Web Encryption (JWE) specification.

Status of this Memo

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This Internet-Draft will expire on March 27, 2015.

Copyright Notice

Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

1.  Introduction
    1.1.  Notational Conventions
2.  Terminology
3.  JSON Web Signature (JWS) Overview
    3.1.  JWS Compact Serialization Overview
    3.2.  JWS JSON Serialization Overview
    3.3.  Example JWS
4.  JOSE Header
    4.1.  Registered Header Parameter Names
        4.1.1.  "alg" (Algorithm) Header Parameter
        4.1.2.  "jku" (JWK Set URL) Header Parameter
        4.1.3.  "jwk" (JSON Web Key) Header Parameter
        4.1.4.  "kid" (Key ID) Header Parameter
        4.1.5.  "x5u" (X.509 URL) Header Parameter
        4.1.6.  "x5c" (X.509 Certificate Chain) Header Parameter
        4.1.7.  "x5t" (X.509 Certificate SHA-1 Thumbprint) Header Parameter
        4.1.8.  "x5t#S256" (X.509 Certificate SHA-256 Thumbprint) Header Parameter
        4.1.9.  "typ" (Type) Header Parameter
        4.1.10.  "cty" (Content Type) Header Parameter
        4.1.11.  "crit" (Critical) Header Parameter
    4.2.  Public Header Parameter Names
    4.3.  Private Header Parameter Names
5.  Producing and Consuming JWSs
    5.1.  Message Signature or MAC Computation
    5.2.  Message Signature or MAC Validation
    5.3.  String Comparison Rules
6.  Key Identification
7.  Serializations
    7.1.  JWS Compact Serialization
    7.2.  JWS JSON Serialization
8.  TLS Requirements
9.  IANA Considerations
    9.1.  JSON Web Signature and Encryption Header Parameters Registry
        9.1.1.  Registration Template
        9.1.2.  Initial Registry Contents
    9.2.  Media Type Registration
        9.2.1.  Registry Contents
10.  Security Considerations
    10.1.  Key Entropy and Random Values
    10.2.  Key Protection
    10.3.  Key Origin Authentication
    10.4.  Cryptographic Agility
    10.5.  Differences between Digital Signatures and MACs
    10.6.  Algorithm Validation
    10.7.  Algorithm Protection
    10.8.  Chosen Plaintext Attacks
    10.9.  Timing Attacks
    10.10.  Replay Protection
    10.11.  SHA-1 Certificate Thumbprints
    10.12.  JSON Security Considerations
    10.13.  Unicode Comparison Security Considerations
11.  References
    11.1.  Normative References
    11.2.  Informative References
Appendix A.  JWS Examples
    A.1.  Example JWS using HMAC SHA-256
        A.1.1.  Encoding
        A.1.2.  Validating
    A.2.  Example JWS using RSASSA-PKCS-v1_5 SHA-256
        A.2.1.  Encoding
        A.2.2.  Validating
    A.3.  Example JWS using ECDSA P-256 SHA-256
        A.3.1.  Encoding
        A.3.2.  Validating
    A.4.  Example JWS using ECDSA P-521 SHA-512
        A.4.1.  Encoding
        A.4.2.  Validating
    A.5.  Example Unsecured JWS
    A.6.  Example JWS Using JWS JSON Serialization
        A.6.1.  JWS Per-Signature Protected Headers
        A.6.2.  JWS Per-Signature Unprotected Headers
        A.6.3.  Complete JOSE Header Values
        A.6.4.  Complete JWS JSON Serialization Representation
Appendix B.  "x5c" (X.509 Certificate Chain) Example
Appendix C.  Notes on implementing base64url encoding without padding
Appendix D.  Notes on Key Selection
Appendix E.  Negative Test Case for "crit" Header Parameter
Appendix F.  Detached Content
Appendix G.  Acknowledgements
Appendix H.  Document History
§  Authors' Addresses

1.  Introduction

JSON Web Signature (JWS) represents content secured with digital signatures or Message Authentication Codes (MACs) using JavaScript Object Notation (JSON) [RFC7159] (Bray, T., “The JavaScript Object Notation (JSON) Data Interchange Format,” March 2014.) based data structures. The JWS cryptographic mechanisms provide integrity protection for an arbitrary sequence of octets. See Section 10.5 (Differences between Digital Signatures and MACs) for a discussion on the differences between Digital Signatures and MACs.

Two closely related serializations for JWS objects are defined. The JWS Compact Serialization is a compact, URL-safe representation intended for space constrained environments such as HTTP Authorization headers and URI query parameters. The JWS JSON Serialization represents JWS objects as JSON objects and enables multiple signatures and/or MACs to be applied to the same content. Both share the same cryptographic underpinnings.

Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) [JWA] (Jones, M., “JSON Web Algorithms (JWA),” September 2014.) specification and an IANA registry defined by that specification. Related encryption capabilities are described in the separate JSON Web Encryption (JWE) [JWE] (Jones, M. and J. Hildebrand, “JSON Web Encryption (JWE),” September 2014.) specification.

Names defined by this specification are short because a core goal is for the resulting representations to be compact.

1.1.  Notational Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "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] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.). If these words are used without being spelled in uppercase then they are to be interpreted with their normal natural language meanings.

BASE64URL(OCTETS) denotes the base64url encoding of OCTETS, per Section 2 (Terminology).

UTF8(STRING) denotes the octets of the UTF-8 [RFC3629] (Yergeau, F., “UTF-8, a transformation format of ISO 10646,” November 2003.) representation of STRING.

ASCII(STRING) denotes the octets of the ASCII [USASCII] (American National Standards Institute, “Coded Character Set -- 7-bit American Standard Code for Information Interchange,” 1986.) representation of STRING.

The concatenation of two values A and B is denoted as A || B.

2.  Terminology

These terms are defined by this specification:

JSON Web Signature (JWS)

A data structure representing a digitally signed or MACed message.

JOSE Header

JSON object containing the parameters describing the cryptographic operations and parameters employed. The JOSE Header is comprised of a set of Header Parameters.

JWS Payload

The sequence of octets to be secured -- a.k.a., the message. The payload can contain an arbitrary sequence of octets.

JWS Signature

Digital signature or MAC over the JWS Protected Header and the JWS Payload.

Header Parameter

A name/value pair that is member of the JOSE Header.

JWS Protected Header

JSON object that contains the Header Parameters that are integrity protected by the JWS Signature digital signature or MAC operation. For the JWS Compact Serialization, this comprises the entire JOSE Header. For the JWS JSON Serialization, this is one component of the JOSE Header.

JWS Unprotected Header

JSON object that contains the Header Parameters that are not integrity protected. This can only be present when using the JWS JSON Serialization.

Base64url Encoding

Base64 encoding using the URL- and filename-safe character set defined in Section 5 of RFC 4648 (Josefsson, S., “The Base16, Base32, and Base64 Data Encodings,” October 2006.) [RFC4648], with all trailing '=' characters omitted (as permitted by Section 3.2) and without the inclusion of any line breaks, white space, or other additional characters. (See Appendix C (Notes on implementing base64url encoding without padding) for notes on implementing base64url encoding without padding.)

JWS Signing Input

The input to the digital signature or MAC computation. Its value is ASCII(BASE64URL(UTF8(JWS Protected Header)) || '.' || BASE64URL(JWS Payload)).

JWS Compact Serialization

A representation of the JWS as a compact, URL-safe string.

JWS JSON Serialization

A representation of the JWS as a JSON object. Unlike the JWS Compact Serialization, the JWS JSON Serialization enables multiple digital signatures and/or MACs to be applied to the same content. This representation is neither optimized for compactness nor URL-safe.

Unsecured JWS

A JWS object that provides no integrity protection.

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] (Leach, P., Mealling, M., and R. Salz, “A Universally Unique IDentifier (UUID) URN Namespace,” July 2005.). 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] (Berners-Lee, T., Fielding, R., and L. Masinter, “Uniform Resource Identifier (URI): Generic Syntax,” January 2005.). StringOrURI values are compared as case-sensitive strings with no transformations or canonicalizations applied.

These terms defined by the JSON Web Encryption (JWE) [JWE] (Jones, M. and J. Hildebrand, “JSON Web Encryption (JWE),” September 2014.) specification are incorporated into this specification: "JSON Web Encryption (JWE)" and "JWE Compact Serialization".

3.  JSON Web Signature (JWS) Overview

JWS represents digitally signed or MACed content using JSON data structures and base64url encoding. These JSON data structures MAY contain white space and/or line breaks. A JWS represents these logical values (each of which is defined in Section 2 (Terminology)):

• JOSE Header
• JWS Payload
• JWS Signature

For a JWS object, the JOSE Header members are the union of the members of these values (each of which is defined in Section 2 (Terminology)):

• JWS Protected Header
• JWS Unprotected Header

This document defines two serializations for JWS objects: a compact, URL-safe serialization called the JWS Compact Serialization and a JSON serialization called the JWS JSON Serialization. In both serializations, the JWS Protected Header, JWS Payload, and JWS Signature are base64url encoded for transmission, since JSON lacks a way to directly represent arbitrary octet sequences.

3.1.  JWS Compact Serialization Overview

In the JWS Compact Serialization, no JWS Unprotected Header is used. In this case, the JOSE Header and the JWS Protected Header are the same.

In the JWS Compact Serialization, a JWS object is represented as the concatenation:

BASE64URL(UTF8(JWS Protected Header)) || '.' ||

BASE64URL(JWS Payload) || '.' ||

BASE64URL(JWS Signature)

3.2.  JWS JSON Serialization Overview

In the JWS JSON Serialization, one or both of the JWS Protected Header and JWS Unprotected Header MUST be present. In this case, the members of the JOSE Header are the combination of the members of the JWS Protected Header and the JWS Unprotected Header values that are present.

In the JWS JSON Serialization, a JWS object is represented as the combination of these four values,

BASE64URL(UTF8(JWS Protected Header)),

JWS Unprotected Header,

BASE64URL(JWS Payload), and

BASE64URL(JWS Signature),

with the three base64url encoding result strings and the JWS Unprotected Header value being represented as members within a JSON object. The inclusion of some of these values is OPTIONAL. The JWS JSON Serialization can also represent multiple signature and/or MAC values, rather than just one. See Section 7.2 (JWS JSON Serialization) for more information about the JWS JSON Serialization.

3.3.  Example JWS

This section provides an example of a JWS. Its computation is described in more detail in Appendix A.1 (Example JWS using HMAC SHA-256), including specifying the exact octet sequences representing the JSON values used and the key value used.

The following example JWS Protected Header declares that the encoded object is a JSON Web Token (JWT) [JWT] (Jones, M., Bradley, J., and N. Sakimura, “JSON Web Token (JWT),” September 2014.) and the JWS Protected Header and the JWS Payload are secured using the HMAC SHA-256 [RFC2104 (Krawczyk, H., Bellare, M., and R. Canetti, “HMAC: Keyed-Hashing for Message Authentication,” February 1997.), SHS (National Institute of Standards and Technology, “Secure Hash Standard (SHS),” March 2012.)] algorithm:

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

Encoding this JWS Protected Header as BASE64URL(UTF8(JWS Protected Header)) gives this value:

  eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9

The UTF-8 representation of following JSON object is used as the JWS Payload. (Note that the payload can be any content, and need not be a representation of a JSON object.)

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

Encoding this JWS Payload as BASE64URL(JWS Payload) gives this value (with line breaks for display purposes only):

  eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
  cGxlLmNvbS9pc19yb290Ijp0cnVlfQ

Computing the HMAC of the JWS Signing Input ASCII(BASE64URL(UTF8(JWS Protected Header)) || '.' || BASE64URL(JWS Payload)) with the HMAC SHA-256 algorithm using the key specified in Appendix A.1 (Example JWS using HMAC SHA-256) and base64url encoding the result yields this BASE64URL(JWS Signature) value:

  dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk

Concatenating these values in the order Header.Payload.Signature with period ('.') characters between the parts yields this complete JWS representation using the JWS Compact Serialization (with line breaks for display purposes only):

  eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
  .
  eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
  cGxlLmNvbS9pc19yb290Ijp0cnVlfQ
  .
  dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk

See Appendix A (JWS Examples) for additional examples.

4.  JOSE Header

For a JWS object, the members of the JSON object(s) representing the JOSE Header describe the digital signature or MAC applied to the JWS Protected Header and the JWS Payload and optionally additional properties of the JWS. The Header Parameter names within the JOSE Header MUST be unique; recipients MUST either reject JWSs 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] (Ecma International, “ECMAScript Language Specification, 5.1 Edition,” June 2011.).

Implementations are required to understand the specific Header Parameters defined by this specification that are designated as "MUST be understood" and process them in the manner defined in this specification. All other Header Parameters defined by this specification that are not so designated MUST be ignored when not understood. Unless listed as a critical Header Parameter, per Section 4.1.11 ("crit" (Critical) Header Parameter), all Header Parameters not defined by this specification MUST be ignored when not understood.

There are three classes of Header Parameter names: Registered Header Parameter names, Public Header Parameter names, and Private Header Parameter names.

4.1.  Registered Header Parameter Names

The following Header Parameter names for use in JWS objects are registered in the IANA JSON Web Signature and Encryption Header Parameters registry defined in Section 9.1 (JSON Web Signature and Encryption Header Parameters Registry), with meanings as defined below.

As indicated by the common registry, JWSs and JWEs share a common Header Parameter space; when a parameter is used by both specifications, its usage must be compatible between the specifications.

4.1.1.  "alg" (Algorithm) Header Parameter

The alg (algorithm) Header Parameter identifies the cryptographic algorithm used to secure the JWS. The JWS Signature value is not valid if the alg value does not represent a supported algorithm, or if there is not a key for use with that algorithm associated with the party that digitally signed or MACed the content. alg values should either be registered in the IANA JSON Web Signature and Encryption Algorithms registry defined in [JWA] (Jones, M., “JSON Web Algorithms (JWA),” September 2014.) or be a value that contains a Collision-Resistant Name. The alg value is a case-sensitive string containing a StringOrURI value. This Header Parameter MUST be present and MUST be understood and processed by implementations.

A list of defined alg values for this use can be found in the IANA JSON Web Signature and Encryption Algorithms registry defined in [JWA] (Jones, M., “JSON Web Algorithms (JWA),” September 2014.); the initial contents of this registry are the values defined in Section 3.1 of the JSON Web Algorithms (JWA) [JWA] (Jones, M., “JSON Web Algorithms (JWA),” September 2014.) specification.

4.1.2.  "jku" (JWK Set URL) Header Parameter

The jku (JWK Set URL) Header Parameter is a URI [RFC3986] (Berners-Lee, T., Fielding, R., and L. Masinter, “Uniform Resource Identifier (URI): Generic Syntax,” January 2005.) that refers to a resource for a set of JSON-encoded public keys, one of which corresponds to the key used to digitally sign the JWS. The keys MUST be encoded as a JSON Web Key Set (JWK Set) [JWK] (Jones, M., “JSON Web Key (JWK),” September 2014.). The protocol used to acquire the resource MUST provide integrity protection; an HTTP GET request to retrieve the JWK Set MUST use TLS [RFC2818 (Rescorla, E., “HTTP Over TLS,” May 2000.), RFC5246 (Dierks, T. and E. Rescorla, “The Transport Layer Security (TLS) Protocol Version 1.2,” August 2008.)]; the identity of the server MUST be validated, as per Section 6 of RFC 6125 (Saint-Andre, P. and J. Hodges, “Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS),” March 2011.) [RFC6125]. Use of this Header Parameter is OPTIONAL.

4.1.3.  "jwk" (JSON Web Key) Header Parameter

The jwk (JSON Web Key) Header Parameter is the public key that corresponds to the key used to digitally sign the JWS. This key is represented as a JSON Web Key [JWK] (Jones, M., “JSON Web Key (JWK),” September 2014.). Use of this Header Parameter is OPTIONAL.

4.1.4.  "kid" (Key ID) Header Parameter

The kid (key ID) Header Parameter is a hint indicating which key was used to secure the JWS. This parameter allows originators to explicitly signal a change of key to recipients. The structure of the kid value is unspecified. Its value MUST be a string. Use of this Header Parameter is OPTIONAL.

When used with a JWK, the kid value is used to match a JWK kid parameter value.

4.1.5.  "x5u" (X.509 URL) Header Parameter

The x5u (X.509 URL) Header Parameter is a URI [RFC3986] (Berners-Lee, T., Fielding, R., and L. Masinter, “Uniform Resource Identifier (URI): Generic Syntax,” January 2005.) that refers to a resource for the X.509 public key certificate or certificate chain [RFC5280] (Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, “Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile,” May 2008.) corresponding to the key used to digitally sign the JWS. The identified resource MUST provide a representation of the certificate or certificate chain that conforms to RFC 5280 (Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, “Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile,” May 2008.) [RFC5280] in PEM encoded form [RFC1421] (Linn, J., “Privacy Enhancement for Internet Electronic Mail: Part I: Message Encryption and Authentication Procedures,” February 1993.). The certificate containing the public key corresponding to the key used to digitally sign the JWS MUST be the first certificate. This MAY be followed by additional certificates, with each subsequent certificate being the one used to certify the previous one. The protocol used to acquire the resource MUST provide integrity protection; an HTTP GET request to retrieve the certificate MUST use TLS [RFC2818 (Rescorla, E., “HTTP Over TLS,” May 2000.), RFC5246 (Dierks, T. and E. Rescorla, “The Transport Layer Security (TLS) Protocol Version 1.2,” August 2008.)]; the identity of the server MUST be validated, as per Section 6 of RFC 6125 (Saint-Andre, P. and J. Hodges, “Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS),” March 2011.) [RFC6125]. Use of this Header Parameter is OPTIONAL.

4.1.6.  "x5c" (X.509 Certificate Chain) Header Parameter

The x5c (X.509 Certificate Chain) Header Parameter contains the X.509 public key certificate or certificate chain [RFC5280] (Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, “Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile,” May 2008.) corresponding to the key used to digitally sign the JWS. The certificate or certificate chain is represented as a JSON array of certificate value strings. Each string in the array is a base64 encoded ([RFC4648] (Josefsson, S., “The Base16, Base32, and Base64 Data Encodings,” October 2006.) Section 4 -- not base64url encoded) DER [ITU.X690.1994] (International Telecommunications Union, “Information Technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER),” 1994.) PKIX certificate value. The certificate containing the public key corresponding to the key used to digitally sign the JWS MUST be the first certificate. This MAY be followed by additional certificates, with each subsequent certificate being the one used to certify the previous one. The recipient MUST validate the certificate chain according to RFC 5280 (Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, “Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile,” May 2008.) [RFC5280] and reject the signature if any validation failure occurs. Use of this Header Parameter is OPTIONAL.

See Appendix B ("x5c" (X.509 Certificate Chain) Example) for an example x5c value.

4.1.7.  "x5t" (X.509 Certificate SHA-1 Thumbprint) Header Parameter

The x5t (X.509 Certificate SHA-1 Thumbprint) Header Parameter is a base64url encoded SHA-1 thumbprint (a.k.a. digest) of the DER encoding of the X.509 certificate [RFC5280] (Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, “Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile,” May 2008.) corresponding to the key used to digitally sign the JWS. Use of this Header Parameter is OPTIONAL.

4.1.8.  "x5t#S256" (X.509 Certificate SHA-256 Thumbprint) Header Parameter

The x5t#S256 (X.509 Certificate SHA-256 Thumbprint) Header Parameter is a base64url encoded SHA-256 thumbprint (a.k.a. digest) of the DER encoding of the X.509 certificate [RFC5280] (Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, “Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile,” May 2008.) corresponding to the key used to digitally sign the JWS. Use of this Header Parameter is OPTIONAL.

4.1.9.  "typ" (Type) Header Parameter

The typ (type) Header Parameter is used by JWS applications to declare the MIME Media Type [IANA.MediaTypes] (Internet Assigned Numbers Authority (IANA), “MIME Media Types,” 2005.) of this complete JWS object. This is intended for use by the application when more than one kind of object could be present in an application data structure that can contain a JWS object; the application can use this value to disambiguate among the different kinds of objects that might be present. It will typically not be used by applications when the kind of object is already known. This parameter is ignored by JWS implementations; any processing of this parameter is performed by the JWS application. Use of this Header Parameter is OPTIONAL.

Per RFC 2045 (Freed, N. and N. Borenstein, “Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies,” November 1996.) [RFC2045], all media type values, subtype values, and parameter names are case-insensitive. However, parameter values are case-sensitive unless otherwise specified for the specific parameter.

To keep messages compact in common situations, it is RECOMMENDED that senders omit an "application/" prefix of a media type value in a typ Header Parameter when no other '/' appears in the media type value. A recipient using the media type value MUST treat it as if "application/" were prepended to any typ value not containing a '/'. For instance, a typ value of example SHOULD be used to represent the application/example media type; whereas, the media type application/example;part="1/2" cannot be shortened to example;part="1/2".

The typ value JOSE can be used by applications to indicate that this object is a JWS or JWE using the JWS Compact Serialization or the JWE Compact Serialization. The typ value JOSE+JSON can be used by applications to indicate that this object is a JWS or JWE using the JWS JSON Serialization or the JWE JSON Serialization. Other type values can also be used by applications.

4.1.10.  "cty" (Content Type) Header Parameter

The cty (content type) Header Parameter is used by JWS applications to declare the MIME Media Type [IANA.MediaTypes] (Internet Assigned Numbers Authority (IANA), “MIME Media Types,” 2005.) of the secured content (the payload). This is intended for use by the application when more than one kind of object could be present in the JWS payload; the application can use this value to disambiguate among the different kinds of objects that might be present. It will typically not be used by applications when the kind of object is already known. This parameter is ignored by JWS implementations; any processing of this parameter is performed by the JWS application. Use of this Header Parameter is OPTIONAL.

Per RFC 2045 (Freed, N. and N. Borenstein, “Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies,” November 1996.) [RFC2045], all media type values, subtype values, and parameter names are case-insensitive. However, parameter values are case-sensitive unless otherwise specified for the specific parameter.

To keep messages compact in common situations, it is RECOMMENDED that senders omit an "application/" prefix of a media type value in a cty Header Parameter when no other '/' appears in the media type value. A recipient using the media type value MUST treat it as if "application/" were prepended to any cty value not containing a '/'. For instance, a cty value of example SHOULD be used to represent the application/example media type; whereas, the media type application/example;part="1/2" cannot be shortened to example;part="1/2".

4.1.11.  "crit" (Critical) Header Parameter

The crit (critical) Header Parameter indicates that extensions to the initial RFC versions of [[ this specification ]] and [JWA] (Jones, M., “JSON Web Algorithms (JWA),” September 2014.) are being used that MUST be understood and processed. Its value is an array listing the Header Parameter names present in the JOSE Header that use those extensions. If any of the listed extension Header Parameters are not understood and supported by the receiver, it MUST reject the JWS. Senders MUST NOT include Header Parameter names defined by the initial RFC versions of [[ this specification ]] or [JWA] (Jones, M., “JSON Web Algorithms (JWA),” September 2014.) for use with JWS, duplicate names, or names that do not occur as Header Parameter names within the JOSE Header in the crit list. Senders MUST NOT use the empty list [] as the crit value. Recipients MAY reject the JWS if the critical list contains any Header Parameter names defined by the initial RFC versions of [[ this specification ]] or [JWA] (Jones, M., “JSON Web Algorithms (JWA),” September 2014.) for use with JWS, or any other constraints on its use are violated. This Header Parameter MUST be integrity protected, and therefore MUST occur only within the JWS Protected Header, when used. Use of this Header Parameter is OPTIONAL. This Header Parameter MUST be understood and processed by implementations.

An example use, along with a hypothetical exp (expiration-time) field is:

  {"alg":"ES256",
   "crit":["exp"],
   "exp":1363284000
  }

4.2.  Public Header Parameter Names

Additional Header Parameter names can be defined by those using JWSs. However, in order to prevent collisions, any new Header Parameter name should either be registered in the IANA JSON Web Signature and Encryption Header Parameters registry defined in Section 9.1 (JSON Web Signature and Encryption Header Parameters Registry) 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 Header Parameter name.

New Header Parameters should be introduced sparingly, as they can result in non-interoperable JWSs.

4.3.  Private Header Parameter Names

A producer and consumer of a JWS may agree to use Header Parameter names that are Private Names: names that are not Registered Header Parameter names Section 4.1 (Registered Header Parameter Names) or Public Header Parameter names Section 4.2 (Public Header Parameter Names). Unlike Public Header Parameter names, Private Header Parameter names are subject to collision and should be used with caution.

5.  Producing and Consuming JWSs

5.1.  Message Signature or MAC Computation

To create a JWS, 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 the content to be used as the JWS Payload.
2. Compute the encoded payload value BASE64URL(JWS Payload).
3. Create the JSON object(s) containing the desired set of Header Parameters, which together comprise the JOSE Header: the JWS Protected Header, and if the JWS JSON Serialization is being used, the JWS Unprotected Header.
4. Compute the encoded header value BASE64URL(UTF8(JWS Protected Header)). If the JWS Protected Header is not present (which can only happen when using the JWS JSON Serialization and no protected member is present), let this value be the empty string.
5. Compute the JWS Signature in the manner defined for the particular algorithm being used over the JWS Signing Input ASCII(BASE64URL(UTF8(JWS Protected Header)) || '.' || BASE64URL(JWS Payload)). The alg (algorithm) Header Parameter MUST be present in the JOSE Header, with the algorithm value accurately representing the algorithm used to construct the JWS Signature.
6. Compute the encoded signature value BASE64URL(JWS Signature).
7. These three encoded values are used in both the JWS Compact Serialization and the JWS JSON Serialization representations.
8. If the JWS JSON Serialization is being used, repeat this process (steps 3-7) for each digital signature or MAC operation being performed.
9. Create the desired serialized output. The JWS Compact Serialization of this result is BASE64URL(UTF8(JWS Protected Header)) || '.' || BASE64URL(JWS Payload) || '.' || BASE64URL(JWS Signature). The JWS JSON Serialization is described in Section 7.2 (JWS JSON Serialization).

5.2.  Message Signature or MAC Validation

When validating a JWS, 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 signature or MAC cannot be validated.

When there are multiple JWS Signature values, it is an application decision which of the JWS Signature values must successfully validate for the JWS to be accepted. In some cases, all must successfully validate or the JWS will be rejected. In other cases, only a specific JWS signature value needs to be successfully validated. However, in all cases, at least one JWS signature value MUST successfully validate or the JWS MUST be rejected.

1. Parse the JWS representation to extract the serialized values for the components of the JWS. When using the JWS Compact Serialization, these components are the base64url encoded representations of the JWS Protected Header, the JWS Payload, and the JWS Signature, and when using the JWS JSON Serialization, these components also include the unencoded JWS Unprotected Header value. When using the JWS Compact Serialization, the JWS Protected Header, the JWS Payload, and the JWS Signature are represented as base64url encoded values in that order, separated by two period ('.') characters. The JWS JSON Serialization is described in Section 7.2 (JWS JSON Serialization).
2. The encoded representation of the JWS Protected Header MUST be successfully base64url decoded following the restriction that no padding characters have been used.
3. The resulting octet sequence MUST be a UTF-8 encoded representation of a completely valid JSON object conforming to RFC 7159 (Bray, T., “The JavaScript Object Notation (JSON) Data Interchange Format,” March 2014.) [RFC7159], which is the JWS Protected Header.
4. If using the JWS Compact Serialization, let the JOSE Header be the JWS Protected Header. Otherwise, when using the JWS JSON Serialization, let the JOSE Header be the union of the members of the corresponding JWS Protected Header and JWS Unprotected Header, all of which must be completely valid JSON objects.
5. The resulting JOSE Header MUST NOT contain duplicate Header Parameter names. When using the JWS JSON Serialization, this restriction includes that the same Header Parameter name also MUST NOT occur in distinct JSON object values that together comprise the JOSE Header.
6. Verify that the implementation understands and can process all fields that it is required to support, whether required by this specification, by the algorithm being used, or by the crit Header Parameter value, and that the values of those parameters are also understood and supported.
7. The encoded representation of the JWS Payload MUST be successfully base64url decoded following the restriction that no padding characters have been used.
8. The encoded representation of the JWS Signature MUST be successfully base64url decoded following the restriction that no padding characters have been used.
9. Validate the JWS Signature against the JWS Signing Input ASCII(BASE64URL(UTF8(JWS Protected Header)) || '.' || BASE64URL(JWS Payload)) in the manner defined for the algorithm being used, which MUST be accurately represented by the value of the alg (algorithm) Header Parameter, which MUST be present. See Section 10.6 (Algorithm Validation) for security considerations on algorithm validation. Record whether the validation succeeded or not.
10. If the JWS JSON Serialization is being used, repeat this process (steps 4-9) for each digital signature or MAC value contained in the representation.
11. If none of the validations in step 9 succeeded, then the JWS MUST be rejected. Otherwise, in the JWS JSON Serialization case, return a result to the application indicating which of the validations succeeded and failed. In the JWS Compact Serialization case, the result can simply indicate whether the JWS was accepted or rejected.

Finally, note that it is an application decision which algorithms are acceptable in a given context. Even if a JWS can be successfully validated, unless the algorithm(s) used in the JWS are acceptable to the application, it SHOULD reject the JWS.

5.3.  String Comparison Rules

Processing a JWS inevitably requires comparing known strings to members and values in a JSON object. For example, in checking what the algorithm is, the Unicode string alg will be checked against the member names in the JOSE Header to see if there is a matching Header Parameter name. The same process is then used to determine if the value of the alg Header Parameter represents a supported algorithm.

Since the only string comparison operations that are performed are equality and inequality, the same rules can be used for comparing both member names and member values against known strings. The JSON rules for doing member name comparison are described in Section 8.3 of RFC 7159 (Bray, T., “The JavaScript Object Notation (JSON) Data Interchange Format,” March 2014.) [RFC7159].

Also, see the JSON security considerations in Section 10.12 (JSON Security Considerations) and the Unicode security considerations in Section 10.13 (Unicode Comparison Security Considerations).

6.  Key Identification

It is necessary for the recipient of a JWS to be able to determine the key that was employed for the digital signature or MAC operation. The key employed can be identified using the Header Parameter methods described in Section 4.1 (Registered Header Parameter Names) or can be identified using methods that are outside the scope of this specification. Specifically, the Header Parameters jku, jwk, kid, x5u, x5c, x5t, and x5t#S256 can be used to identify the key used. These Header Parameters MUST be integrity protected if the information that they convey is to be utilized in a trust decision.

The sender SHOULD include sufficient information in the Header Parameters to identify the key used, unless the application uses another means or convention to determine the key used. Validation of the signature or MAC fails when the algorithm used requires a key (which is true of all algorithms except for none) and the key used cannot be determined.

The means of exchanging any shared symmetric keys used is outside the scope of this specification.

Also, see Appendix D (Notes on Key Selection) for notes on possible key selection algorithms.

7.  Serializations

JWS objects use one of two serializations, the JWS Compact Serialization or the JWS JSON Serialization. Applications using this specification need to specify what serialization and serialization features are used for that application. For instance, applications might specify that only the JWS JSON Serialization is used, that only JWS JSON Serialization support for a single signature or MAC value is used, or that support for multiple signatures and/or MAC values is used. JWS implementations only need to implement the features needed for the applications they are designed to support.

7.1.  JWS Compact Serialization

The JWS Compact Serialization represents digitally signed or MACed content as a compact, URL-safe string. This string is:

BASE64URL(UTF8(JWS Protected Header)) || '.' ||

BASE64URL(JWS Payload) || '.' ||

BASE64URL(JWS Signature)

Only one signature/MAC is supported by the JWS Compact Serialization and it provides no syntax to represent a JWS Unprotected Header value.

7.2.  JWS JSON Serialization

The JWS JSON Serialization represents digitally signed or MACed content as a JSON object. Content using the JWS JSON Serialization can be secured with more than one digital signature and/or MAC operation. This representation is neither optimized for compactness nor URL-safe.

The following members are defined for use in top-level JSON objects used for the JWS JSON Serialization:

payload

The payload member MUST be present and contain the value BASE64URL(JWS Payload).

signatures

The signatures member value MUST be an array of JSON objects. Each object represents a signature or MAC over the JWS Payload and the JWS Protected Header.

The following members are defined for use in the JSON objects that are elements of the signatures array:

protected

The protected member MUST be present and contain the value BASE64URL(UTF8(JWS Protected Header)) when the JWS Protected Header value is non-empty; otherwise, it MUST be absent. These Header Parameter values are integrity protected.

header

The header member MUST be present and contain the value JWS Unprotected Header when the JWS Unprotected Header value is non-empty; otherwise, it MUST be absent. This value is represented as an unencoded JSON object, rather than as a string. These Header Parameter values are not integrity protected.

signature

The signature member MUST be present and contain the value BASE64URL(JWS Signature).

At least one of the protected and header members MUST be present for each signature/MAC computation so that an alg Header Parameter value is conveyed.

Additional members can be present in both the JSON objects defined above; if not understood by implementations encountering them, they MUST be ignored.

The Header Parameter values used when creating or validating individual signature or MAC values are the union of the two sets of Header Parameter values that may be present: (1) the JWS Protected Header represented in the protected member of the signature/MAC's array element, and (2) the JWS Unprotected Header in the header member of the signature/MAC's array element. The union of these sets of Header Parameters comprises the JOSE Header. The Header Parameter names in the two locations MUST be disjoint.

Each JWS Signature value is computed using the parameters of the corresponding JOSE Header value in the same manner as for the JWS Compact Serialization. This has the desirable property that each JWS Signature value represented in the signatures array is identical to the value that would have been computed for the same parameter in the JWS Compact Serialization, provided that the JWS Protected Header value for that signature/MAC computation (which represents the integrity-protected Header Parameter values) matches that used in the JWS Compact Serialization.

In summary, the syntax of a JWS using the JWS JSON Serialization is as follows:

  {
   "payload":"<payload contents>",
   "signatures":[
    {"protected":"<integrity-protected header 1 contents>",
     "header":<non-integrity-protected header 1 contents>,
     "signature":"<signature 1 contents>"},
    ...
    {"protected":"<integrity-protected header N contents>",
     "header":<non-integrity-protected header N contents>,
     "signature":"<signature N contents>"}]
  }

See Appendix A.6 (Example JWS Using JWS JSON Serialization) for an example of computing a JWS using the JWS JSON Serialization.

8.  TLS Requirements

Implementations MUST support TLS. Which version(s) ought to be implemented will vary over time, and depend on the widespread deployment and known security vulnerabilities at the time of implementation. At the time of this writing, TLS version 1.2 [RFC5246] (Dierks, T. and E. Rescorla, “The Transport Layer Security (TLS) Protocol Version 1.2,” August 2008.) is the most recent version.

To protect against information disclosure and tampering, confidentiality protection MUST be applied using TLS with a ciphersuite that provides confidentiality and integrity protection. See current publications by the IETF TLS working group, including RFC 6176 (Turner, S. and T. Polk, “Prohibiting Secure Sockets Layer (SSL) Version 2.0,” March 2011.) [RFC6176], for guidance on the ciphersuites currently considered to be appropriate for use.

Whenever TLS is used, the identity of the service provider encoded in the TLS server certificate MUST be verified using the procedures described in Section 6 of RFC 6125 (Saint-Andre, P. and J. Hodges, “Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS),” March 2011.) [RFC6125].

9.  IANA Considerations

The following registration procedure is used for all the registries established by this specification.

Values are registered on a Specification Required [RFC5226] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.) basis 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: jose-reg-review. ]]

Within the review period, the Designated Expert(s) will either approve or deny the registration request, communicating this decision to the review list and IANA. Denials should include an explanation and, if applicable, suggestions as to how to make the request successful. 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).

9.1.  JSON Web Signature and Encryption Header Parameters Registry

This specification establishes the IANA JSON Web Signature and Encryption Header Parameters registry for Header Parameter names. The registry records the Header Parameter name and a reference to the specification that defines it. The same Header Parameter name can be registered multiple times, provided that the parameter usage is compatible between the specifications. Different registrations of the same Header Parameter name will typically use different Header Parameter Usage Location(s) values.

9.1.1.  Registration Template

Header Parameter 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.

Header Parameter Description:

Brief description of the Header Parameter (e.g., "Example description").

Header Parameter Usage Location(s):

The Header Parameter usage locations, which should be one or more of the values JWS or JWE.

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.

9.1.2.  Initial Registry Contents

This specification registers the Header Parameter names defined in Section 4.1 (Registered Header Parameter Names) in this registry.

• Header Parameter Name: alg
• Header Parameter Description: Algorithm
• Header Parameter Usage Location(s): JWS
• Change Controller: IESG
• Specification Document(s): Section 4.1.1 ("alg" (Algorithm) Header Parameter) of [[ this document ]]

• Header Parameter Name: jku
• Header Parameter Description: JWK Set URL
• Header Parameter Usage Location(s): JWS
• Change Controller: IESG
• Specification Document(s): Section 4.1.2 ("jku" (JWK Set URL) Header Parameter) of [[ this document ]]

• Header Parameter Name: jwk
• Header Parameter Description: JSON Web Key
• Header Parameter Usage Location(s): JWS
• Change Controller: IESG
• Specification document(s): Section 4.1.3 ("jwk" (JSON Web Key) Header Parameter) of [[ this document ]]

• Header Parameter Name: kid
• Header Parameter Description: Key ID
• Header Parameter Usage Location(s): JWS
• Change Controller: IESG
• Specification Document(s): Section 4.1.4 ("kid" (Key ID) Header Parameter) of [[ this document ]]

• Header Parameter Name: x5u
• Header Parameter Description: X.509 URL
• Header Parameter Usage Location(s): JWS
• Change Controller: IESG
• Specification Document(s): Section 4.1.5 ("x5u" (X.509 URL) Header Parameter) of [[ this document ]]

• Header Parameter Name: x5c
• Header Parameter Description: X.509 Certificate Chain
• Header Parameter Usage Location(s): JWS
• Change Controller: IESG
• Specification Document(s): Section 4.1.6 ("x5c" (X.509 Certificate Chain) Header Parameter) of [[ this document ]]

• Header Parameter Name: x5t
• Header Parameter Description: X.509 Certificate SHA-1 Thumbprint
• Header Parameter Usage Location(s): JWS
• Change Controller: IESG
• Specification Document(s): Section 4.1.7 ("x5t" (X.509 Certificate SHA-1 Thumbprint) Header Parameter) of [[ this document ]]

• Header Parameter Name: x5t#S256
• Header Parameter Description: X.509 Certificate SHA-256 Thumbprint
• Header Parameter Usage Location(s): JWS
• Change Controller: IESG
• Specification Document(s): Section 4.1.8 ("x5t#S256" (X.509 Certificate SHA-256 Thumbprint) Header Parameter) of [[ this document ]]

• Header Parameter Name: typ
• Header Parameter Description: Type
• Header Parameter Usage Location(s): JWS
• Change Controller: IESG
• Specification Document(s): Section 4.1.9 ("typ" (Type) Header Parameter) of [[ this document ]]

• Header Parameter Name: cty
• Header Parameter Description: Content Type
• Header Parameter Usage Location(s): JWS
• Change Controller: IESG
• Specification Document(s): Section 4.1.10 ("cty" (Content Type) Header Parameter) of [[ this document ]]

• Header Parameter Name: crit
• Header Parameter Description: Critical
• Header Parameter Usage Location(s): JWS
• Change Controller: IESG
• Specification Document(s): Section 4.1.11 ("crit" (Critical) Header Parameter) of [[ this document ]]

9.2.  Media Type Registration

9.2.1.  Registry Contents

This specification registers the application/jose Media Type [RFC2046] (Freed, N. and N. Borenstein, “Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types,” November 1996.) in the MIME Media Types registry [IANA.MediaTypes] (Internet Assigned Numbers Authority (IANA), “MIME Media Types,” 2005.), which can be used to indicate that the content is a JWS or JWE object using the JWS Compact Serialization or the JWE Compact Serialization and the application/jose+json Media Type in the MIME Media Types registry, which can be used to indicate that the content is a JWS or JWE object using the JWS JSON Serialization or the JWE JSON Serialization.

• Type name: application
• Subtype name: jose
• Required parameters: n/a
• Optional parameters: n/a
• Encoding considerations: 8bit; application/jose values are encoded as a series of base64url encoded values (some of which may be the empty string) separated by period ('.') characters.
• Security considerations: See the Security Considerations section of [[ this document ]]
• Interoperability considerations: n/a
• Published specification: [[ this document ]]
• Applications that use this media type: OpenID Connect, Mozilla Persona, Salesforce, Google, Android, Windows Azure, Xbox One, and numerous others that use JWTs
• Additional information: Magic number(s): n/a, File extension(s): n/a, Macintosh file type code(s): n/a
• Person & email address to contact for further information: Michael B. Jones, mbj@microsoft.com
• Intended usage: COMMON
• Restrictions on usage: none
• Author: Michael B. Jones, mbj@microsoft.com
• Change Controller: IESG

• Type name: application
• Subtype name: jose+json
• Required parameters: n/a
• Optional parameters: n/a
• Encoding considerations: 8bit; application/jose+json values are represented as a JSON Object; UTF-8 encoding SHOULD be employed for the JSON object.
• Security considerations: See the Security Considerations section of [[ this document ]]
• Interoperability considerations: n/a
• Published specification: [[ this document ]]
• Applications that use this media type: TBD
• Additional information: Magic number(s): n/a, File extension(s): n/a, Macintosh file type code(s): n/a
• Person & email address to contact for further information: Michael B. Jones, mbj@microsoft.com
• Intended usage: COMMON
• Restrictions on usage: none
• Author: Michael B. Jones, mbj@microsoft.com
• Change Controller: IESG

10.  Security Considerations

All of the security issues that are pertinent to any cryptographic application must be addressed by JWS/JWE/JWK agents. Among these issues are protecting the user's asymmetric private and symmetric secret keys and employing countermeasures to various attacks.

All the security considerations in XML DSIG 2.0 (Eastlake, D., Reagle, J., Solo, D., Hirsch, F., Roessler, T., Yiu, K., Datta, P., and S. Cantor, “XML Signature Syntax and Processing Version 2.0,” April 2013.) [W3C.NOTE‑xmldsig‑core2‑20130411], also apply to this specification, other than those that are XML specific. Likewise, many of the best practices documented in XML Signature Best Practices (Hirsch, F. and P. Datta, “XML Signature Best Practices,” April 2013.) [W3C.NOTE‑xmldsig‑bestpractices‑20130411] also apply to this specification, other than those that are XML specific.

10.1.  Key Entropy and Random Values

Keys are only as strong as the amount of entropy used to generate them. A minimum of 128 bits of entropy should be used for all keys, and depending upon the application context, more may be required.

Implementations must randomly generate public/private key pairs, message authentication (MAC) keys, and padding values. The use of inadequate pseudo-random number generators (PRNGs) to generate cryptographic keys can result in little or no security. An attacker may find it much easier to reproduce the PRNG environment that produced the keys, searching the resulting small set of possibilities, rather than brute force searching the whole key space. The generation of quality random numbers is difficult. RFC 4086 (Eastlake, D., Schiller, J., and S. Crocker, “Randomness Requirements for Security,” June 2005.) [RFC4086] offers important guidance in this area.

10.2.  Key Protection

Implementations must protect the signer's private key. Compromise of the signer's private key permits an attacker to masquerade as the signer.

Implementations must protect the message authentication (MAC) key. Compromise of the MAC key may result in undetectable modification of the authenticated content.

10.3.  Key Origin Authentication

The key management technique employed to obtain public keys must authenticate the origin of the key; otherwise, it is unknown what party signed the message.

Likewise, the key management technique employed to distribute MAC keys must provide data origin authentication; otherwise, the contents are delivered with integrity from an unknown source.

10.4.  Cryptographic Agility

See Section 8.1 of [JWA] (Jones, M., “JSON Web Algorithms (JWA),” September 2014.) for security considerations on cryptographic agility.

10.5.  Differences between Digital Signatures and MACs

While MACs and digital signatures can both be used for integrity checking, there are some significant differences between the security properties that each of them provides. These need to be taken into consideration when designing protocols and selecting the algorithms to be used in protocols.

Both signatures and MACs provide for integrity checking -- verifying that the message has not been modified since the integrity value was computed. However, MACs provide for origination identification only under specific circumstances. It can normally be assumed that a private key used for a signature is only in the hands of a single entity (although perhaps a distributed entity, in the case of replicated servers); however, a MAC key needs to be in the hands of all the entities that use it for integrity computation and checking. This means that origination can only be determined if a MAC key is known only to two entities and the receiver knows that it did not create the message. MAC validation cannot be used to prove origination to a third party.

10.6.  Algorithm Validation

The digital signature representations for some algorithms include information about the algorithm used inside the signature value. For instance, signatures produced with RSASSA-PKCS-v1_5 [RFC3447] (Jonsson, J. and B. Kaliski, “Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1,” February 2003.) encode the hash function used and many libraries actually use the hash algorithm specified inside the signature when validating the signature. When using such libraries, as part of the algorithm validation performed, implementations MUST ensure that the algorithm information encoded in the signature corresponds to that specified with the alg Header Parameter. If this is not done, an attacker could claim to have used a strong hash algorithm while actually using a weak one represented in the signature value.

10.7.  Algorithm Protection

In some usages of JWS, there is a risk of algorithm substitution attacks, in which an attacker can use an existing digital signature value with a different signature algorithm to make it appear that a signer has signed something that it has not. These attacks have been discussed in detail in the context of CMS [RFC6211] (Schaad, J., “Cryptographic Message Syntax (CMS) Algorithm Identifier Protection Attribute,” April 2011.). This risk arises when all of the following are true:

• Verifiers of a signature support multiple algorithms.
• Given an existing signature, an attacker can find another payload that produces the same signature value with a different algorithm.
• The payload crafted by the attacker is valid in the application context.

There are several ways for an application to mitigate algorithm substitution attacks:

• Use only digital signature algorithms that are not vulnerable to substitution attacks. Substitution attacks are only feasible if an attacker can compute pre-images for a hash function accepted by the recipient. All JWA-defined signature algorithms use SHA-2 hashes, for which there are no known pre-image attacks, as of the time of this writing.
• Require that the alg Header Parameter be carried in the protected header. (This is always the case when using the JWS Compact Serialization and is the approach taken by CMS [RFC6211] (Schaad, J., “Cryptographic Message Syntax (CMS) Algorithm Identifier Protection Attribute,” April 2011.).)
• Include a field containing the algorithm in the application payload, and require that it be matched with the alg Header Parameter during verification. (This is the approach taken by PKIX [RFC5280] (Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, “Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile,” May 2008.).)

10.8.  Chosen Plaintext Attacks

Creators of JWSs should not allow third parties to insert arbitrary content into the message without adding entropy not controlled by the third party.

10.9.  Timing Attacks

When cryptographic algorithms are implemented in such a way that successful operations take a different amount of time than unsuccessful operations, attackers may be able to use the time difference to obtain information about the keys employed. Therefore, such timing differences must be avoided.

10.10.  Replay Protection

While not directly in scope for this specification, note that applications using JWS (or JWE) objects can thwart replay attacks by including a unique message identifier as integrity-protected content in the JWS (or JWE) message and having the recipient verify that the message has not been previously received or acted upon.

10.11.  SHA-1 Certificate Thumbprints

A SHA-1 hash is used when computing x5t (X.509 Certificate SHA-1 Thumbprint) values, for compatibility reasons. Should an effective means of producing SHA-1 hash collisions be developed, and should an attacker wish to interfere with the use of a known certificate on a given system, this could be accomplished by creating another certificate whose SHA-1 hash value is the same and adding it to the certificate store used by the intended victim. A prerequisite to this attack succeeding is the attacker having write access to the intended victim's certificate store.

Alternatively, the x5t#S256 (X.509 Certificate SHA-256 Thumbprint) Header Parameter could be used instead of x5t. However, at the time of this writing, no development platform is known to support SHA-256 certificate thumbprints.

10.12.  JSON Security Considerations

Strict JSON [RFC7159] (Bray, T., “The JavaScript Object Notation (JSON) Data Interchange Format,” March 2014.) validation is a security requirement. If malformed JSON is received, then the intent of the sender is impossible to reliably discern. Ambiguous and potentially exploitable situations could arise if the JSON parser used does not reject malformed JSON syntax. In particular, any JSON inputs not conforming to the JSON-text syntax defined in RFC 7159 input MUST be rejected in their entirety.

Section 4 of the JSON Data Interchange Format specification [RFC7159] (Bray, T., “The JavaScript Object Notation (JSON) Data Interchange Format,” March 2014.) states "The names within an object SHOULD be unique", whereas this specification states that "Header Parameter names within this object MUST be unique; recipients MUST either reject JWSs 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] (Ecma International, “ECMAScript Language Specification, 5.1 Edition,” June 2011.)". Thus, this specification requires that the Section 4 "SHOULD" be treated as a "MUST" by senders and that it be either treated as a "MUST" or in the manner specified in ECMAScript 5.1 by receivers. Ambiguous and potentially exploitable situations could arise if the JSON parser used does not enforce the uniqueness of member names or returns an unpredictable value for duplicate member names.

Some JSON parsers might not reject input that contains extra significant characters after a valid input. For instance, the input {"tag":"value"}ABCD contains a valid JSON-text object followed by the extra characters ABCD. Such input MUST be rejected in its entirety.

10.13.  Unicode Comparison Security Considerations

Header Parameter names and algorithm names are Unicode strings. For security reasons, the representations of these names must be compared verbatim after performing any escape processing (as per Section 8.3 of RFC 7159 (Bray, T., “The JavaScript Object Notation (JSON) Data Interchange Format,” March 2014.) [RFC7159]). This means, for instance, that these JSON strings must compare as being equal ("sig", "\u0073ig"), whereas these must all compare as being not equal to the first set or to each other ("SIG", "Sig", "si\u0047").

JSON strings can 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, JWS 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.

11.  References

11.1. Normative References

11.2. Informative References

Appendix A.  JWS Examples

This section provides several examples of JWSs. While the first three examples all represent JSON Web Tokens (JWTs) [JWT] (Jones, M., Bradley, J., and N. Sakimura, “JSON Web Token (JWT),” September 2014.), the payload can be any octet sequence, as shown in Appendix A.4 (Example JWS using ECDSA P-521 SHA-512).

A.1.  Example JWS using HMAC SHA-256

A.1.1.  Encoding

The following example JWS Protected Header declares that the data structure is a JSON Web Token (JWT) [JWT] (Jones, M., Bradley, J., and N. Sakimura, “JSON Web Token (JWT),” September 2014.) and the JWS Signing Input is secured using the HMAC SHA-256 algorithm.

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

To remove potential ambiguities in the representation of the JSON object above, the actual octet sequence representing UTF8(JWS Protected Header) used in this example is also included below. (Note that ambiguities can arise due to differing platform representations of line breaks (CRLF versus LF), differing spacing at the beginning and ends of lines, whether the last line has a terminating line break or not, and other causes. In the representation used in this example, the first line has no leading or trailing spaces, a CRLF line break (13, 10) occurs between the first and second lines, the second line has one leading space (32) and no trailing spaces, and the last line does not have a terminating line break.) The octets representing UTF8(JWS Protected Header) in this example (using JSON array notation) are:

[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]

Encoding this JWS Protected Header as BASE64URL(UTF8(JWS Protected Header)) gives this value:

  eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9

The JWS Payload used in this example is the octets of the UTF-8 representation of the JSON object below. (Note that the payload can be any base64url encoded octet sequence, and need not be a base64url encoded JSON object.)

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

The following octet sequence, which is the UTF-8 representation used in this example for the JSON object 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]

Encoding this JWS Protected Header as BASE64URL(UTF8(JWS Protected Header)) gives this value (with line breaks for display purposes only):

  eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
  cGxlLmNvbS9pc19yb290Ijp0cnVlfQ

Combining these as BASE64URL(UTF8(JWS Protected Header)) || '.' || BASE64URL(JWS Payload) gives this string (with line breaks for display purposes only):

  eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
  .
  eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
  cGxlLmNvbS9pc19yb290Ijp0cnVlfQ

The resulting JWS Signing Input value, which is the ASCII representation of above string, is the following octet sequence (using JSON array notation):

[101, 121, 74, 48, 101, 88, 65, 105, 79, 105, 74, 75, 86, 49, 81, 105, 76, 65, 48, 75, 73, 67, 74, 104, 98, 71, 99, 105, 79, 105, 74, 73, 85, 122, 73, 49, 78, 105, 74, 57, 46, 101, 121, 74, 112, 99, 51, 77, 105, 79, 105, 74, 113, 98, 50, 85, 105, 76, 65, 48, 75, 73, 67, 74, 108, 101, 72, 65, 105, 79, 106, 69, 122, 77, 68, 65, 52, 77, 84, 107, 122, 79, 68, 65, 115, 68, 81, 111, 103, 73, 109, 104, 48, 100, 72, 65, 54, 76, 121, 57, 108, 101, 71, 70, 116, 99, 71, 120, 108, 76, 109, 78, 118, 98, 83, 57, 112, 99, 49, 57, 121, 98, 50, 57, 48, 73, 106, 112, 48, 99, 110, 86, 108, 102, 81]

HMACs are generated using keys. This example uses the symmetric key represented in JSON Web Key [JWK] (Jones, M., “JSON Web Key (JWK),” September 2014.) format below (with line breaks within values for display purposes only):

  {"kty":"oct",
   "k":"AyM1SysPpbyDfgZld3umj1qzKObwVMkoqQ-EstJQLr_T-1qS0gZH75
        aKtMN3Yj0iPS4hcgUuTwjAzZr1Z9CAow"
  }

Running the HMAC SHA-256 algorithm on the JWS Signing Input with this key yields this JWS Signature octet sequence:

[116, 24, 223, 180, 151, 153, 224, 37, 79, 250, 96, 125, 216, 173, 187, 186, 22, 212, 37, 77, 105, 214, 191, 240, 91, 88, 5, 88, 83, 132, 141, 121]

Encoding this JWS Signature as BASE64URL(JWS Signature) gives this value:

  dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk

Concatenating these values in the order Header.Payload.Signature with period ('.') characters between the parts yields this complete JWS representation using the JWS Compact Serialization (with line breaks for display purposes only):

  eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
  .
  eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
  cGxlLmNvbS9pc19yb290Ijp0cnVlfQ
  .
  dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk

A.1.2.  Validating

Since the alg Header Parameter is HS256, we validate the HMAC SHA-256 value contained in the JWS Signature.

To validate the HMAC value, we repeat the previous process of using the correct key and the JWS Signing Input (which is the initial substring of the JWS Compact Serialization representation up until but not including the second period character) as input to the HMAC SHA-256 function and then taking the output and determining if it matches the JWS Signature (which is base64url decoded from the value encoded in the JWS representation). If it matches exactly, the HMAC has been validated.

A.2.  Example JWS using RSASSA-PKCS-v1_5 SHA-256

A.2.1.  Encoding

The JWS Protected Header in this example is different from the previous example 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 algorithm employed.) The JWS Protected Header used is:

  {"alg":"RS256"}

The octets representing UTF8(JWS Protected Header) in this example (using JSON array notation) are:

[123, 34, 97, 108, 103, 34, 58, 34, 82, 83, 50, 53, 54, 34, 125]

Encoding this JWS Protected Header as BASE64URL(UTF8(JWS Protected Header)) gives this value:

  eyJhbGciOiJSUzI1NiJ9

The JWS Payload used in this example, which follows, is the same as in the previous example. Since the BASE64URL(JWS Payload) value will therefore be the same, its computation is not repeated here.

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

Combining these as BASE64URL(UTF8(JWS Protected Header)) || '.' || BASE64URL(JWS Payload) gives this string (with line breaks for display purposes only):

  eyJhbGciOiJSUzI1NiJ9
  .
  eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
  cGxlLmNvbS9pc19yb290Ijp0cnVlfQ

The resulting JWS Signing Input value, which is the ASCII representation of above string, is the following octet sequence:

[101, 121, 74, 104, 98, 71, 99, 105, 79, 105, 74, 83, 85, 122, 73, 49, 78, 105, 74, 57, 46, 101, 121, 74, 112, 99, 51, 77, 105, 79, 105, 74, 113, 98, 50, 85, 105, 76, 65, 48, 75, 73, 67, 74, 108, 101, 72, 65, 105, 79, 106, 69, 122, 77, 68, 65, 52, 77, 84, 107, 122, 79, 68, 65, 115, 68, 81, 111, 103, 73, 109, 104, 48, 100, 72, 65, 54, 76, 121, 57, 108, 101, 71, 70, 116, 99, 71, 120, 108, 76, 109, 78, 118, 98, 83, 57, 112, 99, 49, 57, 121, 98, 50, 57, 48, 73, 106, 112, 48, 99, 110, 86, 108, 102, 81]

This example uses the RSA key represented in JSON Web Key [JWK] (Jones, M., “JSON Web Key (JWK),” September 2014.) format below (with line breaks within values for display purposes only):

  {"kty":"RSA",
   "n":"ofgWCuLjybRlzo0tZWJjNiuSfb4p4fAkd_wWJcyQoTbji9k0l8W26mPddx
        HmfHQp-Vaw-4qPCJrcS2mJPMEzP1Pt0Bm4d4QlL-yRT-SFd2lZS-pCgNMs
        D1W_YpRPEwOWvG6b32690r2jZ47soMZo9wGzjb_7OMg0LOL-bSf63kpaSH
        SXndS5z5rexMdbBYUsLA9e-KXBdQOS-UTo7WTBEMa2R2CapHg665xsmtdV
        MTBQY4uDZlxvb3qCo5ZwKh9kG4LT6_I5IhlJH7aGhyxXFvUK-DWNmoudF8
        NAco9_h9iaGNj8q2ethFkMLs91kzk2PAcDTW9gb54h4FRWyuXpoQ",
   "e":"AQAB",
   "d":"Eq5xpGnNCivDflJsRQBXHx1hdR1k6Ulwe2JZD50LpXyWPEAeP88vLNO97I
        jlA7_GQ5sLKMgvfTeXZx9SE-7YwVol2NXOoAJe46sui395IW_GO-pWJ1O0
        BkTGoVEn2bKVRUCgu-GjBVaYLU6f3l9kJfFNS3E0QbVdxzubSu3Mkqzjkn
        439X0M_V51gfpRLI9JYanrC4D4qAdGcopV_0ZHHzQlBjudU2QvXt4ehNYT
        CBr6XCLQUShb1juUO1ZdiYoFaFQT5Tw8bGUl_x_jTj3ccPDVZFD9pIuhLh
        BOneufuBiB4cS98l2SR_RQyGWSeWjnczT0QU91p1DhOVRuOopznQ"
  }

The RSA private key is then passed to the RSA signing function, which also takes the hash type, SHA-256, and the JWS Signing Input as inputs. The result of the digital signature is an octet sequence, which represents a big endian integer. In this example, it is:

[112, 46, 33, 137, 67, 232, 143, 209, 30, 181, 216, 45, 191, 120, 69, 243, 65, 6, 174, 27, 129, 255, 247, 115, 17, 22, 173, 209, 113, 125, 131, 101, 109, 66, 10, 253, 60, 150, 238, 221, 115, 162, 102, 62, 81, 102, 104, 123, 0, 11, 135, 34, 110, 1, 135, 237, 16, 115, 249, 69, 229, 130, 173, 252, 239, 22, 216, 90, 121, 142, 232, 198, 109, 219, 61, 184, 151, 91, 23, 208, 148, 2, 190, 237, 213, 217, 217, 112, 7, 16, 141, 178, 129, 96, 213, 248, 4, 12, 167, 68, 87, 98, 184, 31, 190, 127, 249, 217, 46, 10, 231, 111, 36, 242, 91, 51, 187, 230, 244, 74, 230, 30, 177, 4, 10, 203, 32, 4, 77, 62, 249, 18, 142, 212, 1, 48, 121, 91, 212, 189, 59, 65, 238, 202, 208, 102, 171, 101, 25, 129, 253, 228, 141, 247, 127, 55, 45, 195, 139, 159, 175, 221, 59, 239, 177, 139, 93, 163, 204, 60, 46, 176, 47, 158, 58, 65, 214, 18, 202, 173, 21, 145, 18, 115, 160, 95, 35, 185, 232, 56, 250, 175, 132, 157, 105, 132, 41, 239, 90, 30, 136, 121, 130, 54, 195, 212, 14, 96, 69, 34, 165, 68, 200, 242, 122, 122, 45, 184, 6, 99, 209, 108, 247, 202, 234, 86, 222, 64, 92, 178, 33, 90, 69, 178, 194, 85, 102, 181, 90, 193, 167, 72, 160, 112, 223, 200, 163, 42, 70, 149, 67, 208, 25, 238, 251, 71]

Encoding the signature as BASE64URL(JWS Signature) produces this value (with line breaks for display purposes only):

  cC4hiUPoj9Eetdgtv3hF80EGrhuB__dzERat0XF9g2VtQgr9PJbu3XOiZj5RZmh7
  AAuHIm4Bh-0Qc_lF5YKt_O8W2Fp5jujGbds9uJdbF9CUAr7t1dnZcAcQjbKBYNX4
  BAynRFdiuB--f_nZLgrnbyTyWzO75vRK5h6xBArLIARNPvkSjtQBMHlb1L07Qe7K
  0GarZRmB_eSN9383LcOLn6_dO--xi12jzDwusC-eOkHWEsqtFZESc6BfI7noOPqv
  hJ1phCnvWh6IeYI2w9QOYEUipUTI8np6LbgGY9Fs98rqVt5AXLIhWkWywlVmtVrB
  p0igcN_IoypGlUPQGe77Rw

Concatenating these values in the order Header.Payload.Signature with period ('.') characters between the parts yields this complete JWS representation using the JWS Compact Serialization (with line breaks for display purposes only):

  eyJhbGciOiJSUzI1NiJ9
  .
  eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
  cGxlLmNvbS9pc19yb290Ijp0cnVlfQ
  .
  cC4hiUPoj9Eetdgtv3hF80EGrhuB__dzERat0XF9g2VtQgr9PJbu3XOiZj5RZmh7
  AAuHIm4Bh-0Qc_lF5YKt_O8W2Fp5jujGbds9uJdbF9CUAr7t1dnZcAcQjbKBYNX4
  BAynRFdiuB--f_nZLgrnbyTyWzO75vRK5h6xBArLIARNPvkSjtQBMHlb1L07Qe7K
  0GarZRmB_eSN9383LcOLn6_dO--xi12jzDwusC-eOkHWEsqtFZESc6BfI7noOPqv
  hJ1phCnvWh6IeYI2w9QOYEUipUTI8np6LbgGY9Fs98rqVt5AXLIhWkWywlVmtVrB
  p0igcN_IoypGlUPQGe77Rw

A.2.2.  Validating

Since the alg Header Parameter is RS256, we validate the RSASSA-PKCS-v1_5 SHA-256 digital signature contained in the JWS Signature.

Validating the JWS Signature is a bit different from the previous example. We pass the public key (n, e), the JWS Signature (which is base64url decoded from the value encoded in the JWS representation), and the JWS Signing Input (which is the initial substring of the JWS Compact Serialization representation up until but not including the second period character) to an RSASSA-PKCS-v1_5 signature verifier that has been configured to use the SHA-256 hash function.

A.3.  Example JWS using ECDSA P-256 SHA-256

A.3.1.  Encoding

The JWS Protected Header for this example differs from the previous example because a different algorithm is being used. The JWS Protected Header used is:

  {"alg":"ES256"}

The octets representing UTF8(JWS Protected Header) in this example (using JSON array notation) are:

[123, 34, 97, 108, 103, 34, 58, 34, 69, 83, 50, 53, 54, 34, 125]

Encoding this JWS Protected Header as BASE64URL(UTF8(JWS Protected Header)) gives this value:

  eyJhbGciOiJFUzI1NiJ9

The JWS Payload used in this example, which follows, is the same as in the previous examples. Since the BASE64URL(JWS Payload) value will therefore be the same, its computation is not repeated here.

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

Combining these as BASE64URL(UTF8(JWS Protected Header)) || '.' || BASE64URL(JWS Payload) gives this string (with line breaks for display purposes only):

  eyJhbGciOiJFUzI1NiJ9
  .
  eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
  cGxlLmNvbS9pc19yb290Ijp0cnVlfQ

The resulting JWS Signing Input value, which is the ASCII representation of above string, is the following octet sequence:

[101, 121, 74, 104, 98, 71, 99, 105, 79, 105, 74, 70, 85, 122, 73, 49, 78, 105, 74, 57, 46, 101, 121, 74, 112, 99, 51, 77, 105, 79, 105, 74, 113, 98, 50, 85, 105, 76, 65, 48, 75, 73, 67, 74, 108, 101, 72, 65, 105, 79, 106, 69, 122, 77, 68, 65, 52, 77, 84, 107, 122, 79, 68, 65, 115, 68, 81, 111, 103, 73, 109, 104, 48, 100, 72, 65, 54, 76, 121, 57, 108, 101, 71, 70, 116, 99, 71, 120, 108, 76, 109, 78, 118, 98, 83, 57, 112, 99, 49, 57, 121, 98, 50, 57, 48, 73, 106, 112, 48, 99, 110, 86, 108, 102, 81]

This example uses the elliptic curve key represented in JSON Web Key [JWK] (Jones, M., “JSON Web Key (JWK),” September 2014.) format below:

  {"kty":"EC",
   "crv":"P-256",
   "x":"f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU",
   "y":"x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0",
   "d":"jpsQnnGQmL-YBIffH1136cspYG6-0iY7X1fCE9-E9LI"
  }

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 JWS Signing Input as inputs. The result of the digital signature is the EC point (R, S), where R and S are unsigned integers. In this example, the R and S values, given as octet sequences representing big endian integers are:

The JWS Signature is the value R || S. Encoding the signature as BASE64URL(JWS Signature) produces this value (with line breaks for display purposes only):

  DtEhU3ljbEg8L38VWAfUAqOyKAM6-Xx-F4GawxaepmXFCgfTjDxw5djxLa8ISlSA
  pmWQxfKTUJqPP3-Kg6NU1Q

Concatenating these values in the order Header.Payload.Signature with period ('.') characters between the parts yields this complete JWS representation using the JWS Compact Serialization (with line breaks for display purposes only):

  eyJhbGciOiJFUzI1NiJ9
  .
  eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
  cGxlLmNvbS9pc19yb290Ijp0cnVlfQ
  .
  DtEhU3ljbEg8L38VWAfUAqOyKAM6-Xx-F4GawxaepmXFCgfTjDxw5djxLa8ISlSA
  pmWQxfKTUJqPP3-Kg6NU1Q

A.3.2.  Validating

Since the alg Header Parameter is ES256, we validate the ECDSA P-256 SHA-256 digital signature contained in the JWS Signature.

Validating the JWS Signature is a bit different from the previous examples. We need to split the 64 member octet sequence of the JWS Signature (which is base64url decoded from the value encoded in the JWS representation) into two 32 octet sequences, the first representing R and the second S. We then pass the public key (x, y), the signature (R, S), and the JWS Signing Input (which is the initial substring of the JWS Compact Serialization representation up until but not including the second period character) to an ECDSA signature verifier that has been configured to use the P-256 curve with the SHA-256 hash function.

A.4.  Example JWS using ECDSA P-521 SHA-512

A.4.1.  Encoding

The JWS Protected Header for this example differs from the previous example because different ECDSA curves and hash functions are used. The JWS Protected Header used is:

  {"alg":"ES512"}

The octets representing UTF8(JWS Protected Header) in this example (using JSON array notation) are:

[123, 34, 97, 108, 103, 34, 58, 34, 69, 83, 53, 49, 50, 34, 125]

Encoding this JWS Protected Header as BASE64URL(UTF8(JWS Protected Header)) gives this value:

  eyJhbGciOiJFUzUxMiJ9

The JWS Payload used in this example, is the ASCII string "Payload". The representation of this string is the octet sequence:

[80, 97, 121, 108, 111, 97, 100]

Encoding this JWS Payload as BASE64URL(JWS Payload) gives this value:

  UGF5bG9hZA

Combining these as BASE64URL(UTF8(JWS Protected Header)) || '.' || BASE64URL(JWS Payload) gives this string:

  eyJhbGciOiJFUzUxMiJ9.UGF5bG9hZA

The resulting JWS Signing Input value, which is the ASCII representation of above string, is the following octet sequence:

[101, 121, 74, 104, 98, 71, 99, 105, 79, 105, 74, 70, 85, 122, 85, 120, 77, 105, 74, 57, 46, 85, 71, 70, 53, 98, 71, 57, 104, 90, 65]

This example uses the elliptic curve key represented in JSON Web Key [JWK] (Jones, M., “JSON Web Key (JWK),” September 2014.) format below (with line breaks within values for display purposes only):

  {"kty":"EC",
   "crv":"P-521",
   "x":"AekpBQ8ST8a8VcfVOTNl353vSrDCLLJXmPk06wTjxrrjcBpXp5EOnYG_
        NjFZ6OvLFV1jSfS9tsz4qUxcWceqwQGk",
   "y":"ADSmRA43Z1DSNx_RvcLI87cdL07l6jQyyBXMoxVg_l2Th-x3S1WDhjDl
        y79ajL4Kkd0AZMaZmh9ubmf63e3kyMj2",
   "d":"AY5pb7A0UFiB3RELSD64fTLOSV_jazdF7fLYyuTw8lOfRhWg6Y6rUrPA
        xerEzgdRhajnu0ferB0d53vM9mE15j2C"
  }

The ECDSA private part d is then passed to an ECDSA signing function, which also takes the curve type, P-521, the hash type, SHA-512, and the JWS Signing Input as inputs. The result of the digital signature is the EC point (R, S), where R and S are unsigned integers. In this example, the R and S values, given as octet sequences representing big endian integers are:

The JWS Signature is the value R || S. Encoding the signature as BASE64URL(JWS Signature) produces this value (with line breaks for display purposes only):

  AdwMgeerwtHoh-l192l60hp9wAHZFVJbLfD_UxMi70cwnZOYaRI1bKPWROc-mZZq
  wqT2SI-KGDKB34XO0aw_7XdtAG8GaSwFKdCAPZgoXD2YBJZCPEX3xKpRwcdOO8Kp
  EHwJjyqOgzDO7iKvU8vcnwNrmxYbSW9ERBXukOXolLzeO_Jn

Concatenating these values in the order Header.Payload.Signature with period ('.') characters between the parts yields this complete JWS representation using the JWS Compact Serialization (with line breaks for display purposes only):

  eyJhbGciOiJFUzUxMiJ9
  .
  UGF5bG9hZA
  .
  AdwMgeerwtHoh-l192l60hp9wAHZFVJbLfD_UxMi70cwnZOYaRI1bKPWROc-mZZq
  wqT2SI-KGDKB34XO0aw_7XdtAG8GaSwFKdCAPZgoXD2YBJZCPEX3xKpRwcdOO8Kp
  EHwJjyqOgzDO7iKvU8vcnwNrmxYbSW9ERBXukOXolLzeO_Jn

A.4.2.  Validating

Since the alg Header Parameter is ES512, we validate the ECDSA P-521 SHA-512 digital signature contained in the JWS Signature.

Validating this JWS Signature is very similar to the previous example. We need to split the 132 member octet sequence of the JWS Signature into two 66 octet sequences, the first representing R and the second S. We then pass the public key (x, y), the signature (R, S), and the JWS Signing Input to an ECDSA signature verifier that has been configured to use the P-521 curve with the SHA-512 hash function.

A.5.  Example Unsecured JWS

The following example JWS Protected Header declares that the encoded object is an Unsecured JWS:

  {"alg":"none"}

Encoding this JWS Protected Header as BASE64URL(UTF8(JWS Protected Header)) gives this value:

  eyJhbGciOiJub25lIn0

The JWS Payload used in this example, which follows, is the same as in the previous examples. Since the BASE64URL(JWS Payload) value will therefore be the same, its computation is not repeated here.

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

The JWS Signature is the empty octet string and BASE64URL(JWS Signature) is the empty string.

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

  eyJhbGciOiJub25lIn0
  .
  eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
  cGxlLmNvbS9pc19yb290Ijp0cnVlfQ
  .

A.6.  Example JWS Using JWS JSON Serialization

This section contains an example using the JWS JSON Serialization. This example demonstrates the capability for conveying multiple digital signatures and/or MACs for the same payload.

The JWS Payload used in this example is the same as that used in the examples in Appendix A.2 (Example JWS using RSASSA-PKCS-v1_5 SHA-256) and Appendix A.3 (Example JWS using ECDSA P-256 SHA-256) (with line breaks for display purposes only):

  eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
  cGxlLmNvbS9pc19yb290Ijp0cnVlfQ

Two digital signatures are used in this example: the first using RSASSA-PKCS-v1_5 SHA-256 and the second using ECDSA P-256 SHA-256. For the first, the JWS Protected Header and key are the same as in Appendix A.2 (Example JWS using RSASSA-PKCS-v1_5 SHA-256), resulting in the same JWS Signature value; therefore, its computation is not repeated here. For the second, the JWS Protected Header and key are the same as in Appendix A.3 (Example JWS using ECDSA P-256 SHA-256), resulting in the same JWS Signature value; therefore, its computation is not repeated here.

A.6.1.  JWS Per-Signature Protected Headers

The JWS Protected Header value used for the first signature is:

  {"alg":"RS256"}

Encoding this JWS Protected Header as BASE64URL(UTF8(JWS Protected Header)) gives this value:

  eyJhbGciOiJSUzI1NiJ9

The JWS Protected Header value used for the second signature is:

  {"alg":"ES256"}

Encoding this JWS Protected Header as BASE64URL(UTF8(JWS Protected Header)) gives this value:

  eyJhbGciOiJFUzI1NiJ9

A.6.2.  JWS Per-Signature Unprotected Headers

Key ID values are supplied for both keys using per-signature Header Parameters. The two values used to represent these Key IDs are:

  {"kid":"2010-12-29"}

and

  {"kid":"e9bc097a-ce51-4036-9562-d2ade882db0d"}

A.6.3.  Complete JOSE Header Values

Combining the protected and unprotected header values supplied, the JOSE Header values used for the first and second signatures respectively are:

  {"alg":"RS256",
   "kid":"2010-12-29"}

and

  {"alg":"ES256",
   "kid":"e9bc097a-ce51-4036-9562-d2ade882db0d"}

A.6.4.  Complete JWS JSON Serialization Representation

The complete JSON Web Signature JSON Serialization for these values is as follows (with line breaks within values for display purposes only):

  {"payload":
    "eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGF
     tcGxlLmNvbS9pc19yb290Ijp0cnVlfQ",
   "signatures":[
    {"protected":"eyJhbGciOiJSUzI1NiJ9",
     "header":
      {"kid":"2010-12-29"},
     "signature":
      "cC4hiUPoj9Eetdgtv3hF80EGrhuB__dzERat0XF9g2VtQgr9PJbu3XOiZj5RZ
       mh7AAuHIm4Bh-0Qc_lF5YKt_O8W2Fp5jujGbds9uJdbF9CUAr7t1dnZcAcQjb
       KBYNX4BAynRFdiuB--f_nZLgrnbyTyWzO75vRK5h6xBArLIARNPvkSjtQBMHl
       b1L07Qe7K0GarZRmB_eSN9383LcOLn6_dO--xi12jzDwusC-eOkHWEsqtFZES
       c6BfI7noOPqvhJ1phCnvWh6IeYI2w9QOYEUipUTI8np6LbgGY9Fs98rqVt5AX
       LIhWkWywlVmtVrBp0igcN_IoypGlUPQGe77Rw"},
    {"protected":"eyJhbGciOiJFUzI1NiJ9",
     "header":
      {"kid":"e9bc097a-ce51-4036-9562-d2ade882db0d"},
     "signature":
      "DtEhU3ljbEg8L38VWAfUAqOyKAM6-Xx-F4GawxaepmXFCgfTjDxw5djxLa8IS
       lSApmWQxfKTUJqPP3-Kg6NU1Q"}]
  }

Appendix B.  "x5c" (X.509 Certificate Chain) Example

The JSON array below is an example of a certificate chain that could be used as the value of an x5c (X.509 Certificate Chain) Header Parameter, per Section 4.1.6 ("x5c" (X.509 Certificate Chain) Header Parameter). Note that since these strings contain base64 encoded (not base64url encoded) values, they are allowed to contain white space and line breaks.

  ["MIIE3jCCA8agAwIBAgICAwEwDQYJKoZIhvcNAQEFBQAwYzELMAkGA1UEBhMCVVM
    xITAfBgNVBAoTGFRoZSBHbyBEYWRkeSBHcm91cCwgSW5jLjExMC8GA1UECxMoR2
    8gRGFkZHkgQ2xhc3MgMiBDZXJ0aWZpY2F0aW9uIEF1dGhvcml0eTAeFw0wNjExM
    TYwMTU0MzdaFw0yNjExMTYwMTU0MzdaMIHKMQswCQYDVQQGEwJVUzEQMA4GA1UE
    CBMHQXJpem9uYTETMBEGA1UEBxMKU2NvdHRzZGFsZTEaMBgGA1UEChMRR29EYWR
    keS5jb20sIEluYy4xMzAxBgNVBAsTKmh0dHA6Ly9jZXJ0aWZpY2F0ZXMuZ29kYW
    RkeS5jb20vcmVwb3NpdG9yeTEwMC4GA1UEAxMnR28gRGFkZHkgU2VjdXJlIENlc
    nRpZmljYXRpb24gQXV0aG9yaXR5MREwDwYDVQQFEwgwNzk2OTI4NzCCASIwDQYJ
    KoZIhvcNAQEBBQADggEPADCCAQoCggEBAMQt1RWMnCZM7DI161+4WQFapmGBWTt
    wY6vj3D3HKrjJM9N55DrtPDAjhI6zMBS2sofDPZVUBJ7fmd0LJR4h3mUpfjWoqV
    Tr9vcyOdQmVZWt7/v+WIbXnvQAjYwqDL1CBM6nPwT27oDyqu9SoWlm2r4arV3aL
    GbqGmu75RpRSgAvSMeYddi5Kcju+GZtCpyz8/x4fKL4o/K1w/O5epHBp+YlLpyo
    7RJlbmr2EkRTcDCVw5wrWCs9CHRK8r5RsL+H0EwnWGu1NcWdrxcx+AuP7q2BNgW
    JCJjPOq8lh8BJ6qf9Z/dFjpfMFDniNoW1fho3/Rb2cRGadDAW/hOUoz+EDU8CAw
    EAAaOCATIwggEuMB0GA1UdDgQWBBT9rGEyk2xF1uLuhV+auud2mWjM5zAfBgNVH
    SMEGDAWgBTSxLDSkdRMEXGzYcs9of7dqGrU4zASBgNVHRMBAf8ECDAGAQH/AgEA
    MDMGCCsGAQUFBwEBBCcwJTAjBggrBgEFBQcwAYYXaHR0cDovL29jc3AuZ29kYWR
    keS5jb20wRgYDVR0fBD8wPTA7oDmgN4Y1aHR0cDovL2NlcnRpZmljYXRlcy5nb2
    RhZGR5LmNvbS9yZXBvc2l0b3J5L2dkcm9vdC5jcmwwSwYDVR0gBEQwQjBABgRVH
    SAAMDgwNgYIKwYBBQUHAgEWKmh0dHA6Ly9jZXJ0aWZpY2F0ZXMuZ29kYWRkeS5j
    b20vcmVwb3NpdG9yeTAOBgNVHQ8BAf8EBAMCAQYwDQYJKoZIhvcNAQEFBQADggE
    BANKGwOy9+aG2Z+5mC6IGOgRQjhVyrEp0lVPLN8tESe8HkGsz2ZbwlFalEzAFPI
    UyIXvJxwqoJKSQ3kbTJSMUA2fCENZvD117esyfxVgqwcSeIaha86ykRvOe5GPLL
    5CkKSkB2XIsKd83ASe8T+5o0yGPwLPk9Qnt0hCqU7S+8MxZC9Y7lhyVJEnfzuz9
    p0iRFEUOOjZv2kWzRaJBydTXRE4+uXR21aITVSzGh6O1mawGhId/dQb8vxRMDsx
    uxN89txJx9OjxUUAiKEngHUuHqDTMBqLdElrRhjZkAzVvb3du6/KFUJheqwNTrZ
    EjYx8WnM25sgVjOuH0aBsXBTWVU+4=",
   "MIIE+zCCBGSgAwIBAgICAQ0wDQYJKoZIhvcNAQEFBQAwgbsxJDAiBgNVBAcTG1Z
    hbGlDZXJ0IFZhbGlkYXRpb24gTmV0d29yazEXMBUGA1UEChMOVmFsaUNlcnQsIE
    luYy4xNTAzBgNVBAsTLFZhbGlDZXJ0IENsYXNzIDIgUG9saWN5IFZhbGlkYXRpb
    24gQXV0aG9yaXR5MSEwHwYDVQQDExhodHRwOi8vd3d3LnZhbGljZXJ0LmNvbS8x
    IDAeBgkqhkiG9w0BCQEWEWluZm9AdmFsaWNlcnQuY29tMB4XDTA0MDYyOTE3MDY
    yMFoXDTI0MDYyOTE3MDYyMFowYzELMAkGA1UEBhMCVVMxITAfBgNVBAoTGFRoZS
    BHbyBEYWRkeSBHcm91cCwgSW5jLjExMC8GA1UECxMoR28gRGFkZHkgQ2xhc3MgM
    iBDZXJ0aWZpY2F0aW9uIEF1dGhvcml0eTCCASAwDQYJKoZIhvcNAQEBBQADggEN
    ADCCAQgCggEBAN6d1+pXGEmhW+vXX0iG6r7d/+TvZxz0ZWizV3GgXne77ZtJ6XC
    APVYYYwhv2vLM0D9/AlQiVBDYsoHUwHU9S3/Hd8M+eKsaA7Ugay9qK7HFiH7Eux
    6wwdhFJ2+qN1j3hybX2C32qRe3H3I2TqYXP2WYktsqbl2i/ojgC95/5Y0V4evLO
    tXiEqITLdiOr18SPaAIBQi2XKVlOARFmR6jYGB0xUGlcmIbYsUfb18aQr4CUWWo
    riMYavx4A6lNf4DD+qta/KFApMoZFv6yyO9ecw3ud72a9nmYvLEHZ6IVDd2gWMZ
    Eewo+YihfukEHU1jPEX44dMX4/7VpkI+EdOqXG68CAQOjggHhMIIB3TAdBgNVHQ
    4EFgQU0sSw0pHUTBFxs2HLPaH+3ahq1OMwgdIGA1UdIwSByjCBx6GBwaSBvjCBu
    zEkMCIGA1UEBxMbVmFsaUNlcnQgVmFsaWRhdGlvbiBOZXR3b3JrMRcwFQYDVQQK
    Ew5WYWxpQ2VydCwgSW5jLjE1MDMGA1UECxMsVmFsaUNlcnQgQ2xhc3MgMiBQb2x
    pY3kgVmFsaWRhdGlvbiBBdXRob3JpdHkxITAfBgNVBAMTGGh0dHA6Ly93d3cudm
    FsaWNlcnQuY29tLzEgMB4GCSqGSIb3DQEJARYRaW5mb0B2YWxpY2VydC5jb22CA
    QEwDwYDVR0TAQH/BAUwAwEB/zAzBggrBgEFBQcBAQQnMCUwIwYIKwYBBQUHMAGG
    F2h0dHA6Ly9vY3NwLmdvZGFkZHkuY29tMEQGA1UdHwQ9MDswOaA3oDWGM2h0dHA
    6Ly9jZXJ0aWZpY2F0ZXMuZ29kYWRkeS5jb20vcmVwb3NpdG9yeS9yb290LmNybD
    BLBgNVHSAERDBCMEAGBFUdIAAwODA2BggrBgEFBQcCARYqaHR0cDovL2NlcnRpZ
    mljYXRlcy5nb2RhZGR5LmNvbS9yZXBvc2l0b3J5MA4GA1UdDwEB/wQEAwIBBjAN
    BgkqhkiG9w0BAQUFAAOBgQC1QPmnHfbq/qQaQlpE9xXUhUaJwL6e4+PrxeNYiY+
    Sn1eocSxI0YGyeR+sBjUZsE4OWBsUs5iB0QQeyAfJg594RAoYC5jcdnplDQ1tgM
    QLARzLrUc+cb53S8wGd9D0VmsfSxOaFIqII6hR8INMqzW/Rn453HWkrugp++85j
    09VZw==",
   "MIIC5zCCAlACAQEwDQYJKoZIhvcNAQEFBQAwgbsxJDAiBgNVBAcTG1ZhbGlDZXJ
    0IFZhbGlkYXRpb24gTmV0d29yazEXMBUGA1UEChMOVmFsaUNlcnQsIEluYy4xNT
    AzBgNVBAsTLFZhbGlDZXJ0IENsYXNzIDIgUG9saWN5IFZhbGlkYXRpb24gQXV0a
    G9yaXR5MSEwHwYDVQQDExhodHRwOi8vd3d3LnZhbGljZXJ0LmNvbS8xIDAeBgkq
    hkiG9w0BCQEWEWluZm9AdmFsaWNlcnQuY29tMB4XDTk5MDYyNjAwMTk1NFoXDTE
    5MDYyNjAwMTk1NFowgbsxJDAiBgNVBAcTG1ZhbGlDZXJ0IFZhbGlkYXRpb24gTm
    V0d29yazEXMBUGA1UEChMOVmFsaUNlcnQsIEluYy4xNTAzBgNVBAsTLFZhbGlDZ
    XJ0IENsYXNzIDIgUG9saWN5IFZhbGlkYXRpb24gQXV0aG9yaXR5MSEwHwYDVQQD
    ExhodHRwOi8vd3d3LnZhbGljZXJ0LmNvbS8xIDAeBgkqhkiG9w0BCQEWEWluZm9
    AdmFsaWNlcnQuY29tMIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDOOnHK5a
    vIWZJV16vYdA757tn2VUdZZUcOBVXc65g2PFxTXdMwzzjsvUGJ7SVCCSRrCl6zf
    N1SLUzm1NZ9WlmpZdRJEy0kTRxQb7XBhVQ7/nHk01xC+YDgkRoKWzk2Z/M/VXwb
    P7RfZHM047QSv4dk+NoS/zcnwbNDu+97bi5p9wIDAQABMA0GCSqGSIb3DQEBBQU
    AA4GBADt/UG9vUJSZSWI4OB9L+KXIPqeCgfYrx+jFzug6EILLGACOTb2oWH+heQ
    C1u+mNr0HZDzTuIYEZoDJJKPTEjlbVUjP9UNV+mWwD5MlM/Mtsq2azSiGM5bUMM
    j4QssxsodyamEwCW/POuZ6lcg5Ktz885hZo+L7tdEy8W9ViH0Pd"]

Appendix C.  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.

  static string base64urlencode(byte [] arg)
  {
    string s = Convert.ToBase64String(arg); // Regular 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 octet sequence below encodes into the string below, which when decoded, reproduces the octet sequence.

3 236 255 224 193

A-z_4ME

Appendix D.  Notes on Key Selection

This appendix describes a set of possible algorithms for selecting the key to be used to validate the digital signature or MAC of a JWS object or for selecting the key to be used to decrypt a JWE object. This guidance describes a family of possible algorithms, rather than a single algorithm, because in different contexts, not all the sources of keys will be used, they can be tried in different orders, and sometimes not all the collected keys will be tried; hence, different algorithms will be used in different application contexts.

The steps below are described for illustration purposes only; specific applications can and are likely to use different algorithms or perform some of the steps in different orders. Specific applications will frequently have a much simpler method of determining the keys to use, as there may be one or two key selection methods that are profiled for the application's use. This appendix supplements the normative information on key location in Section 6 (Key Identification).

These algorithms include the following steps. Note that the steps can be performed in any order and do not need to be treated as distinct. For example, keys can be tried as soon as they are found, rather than collecting all the keys before trying any.

1. Collect the set of potentially applicable keys. Sources of keys may include:
   • Keys supplied by the application protocol being used.
   • Keys referenced by the jku (JWK Set URL) Header Parameter.
   • The key provided by the jwk (JSON Web Key) Header Parameter.
   • The key referenced by the x5u (X.509 URL) Header Parameter.
   • The key provided by the x5c (X.509 Certificate Chain) Header Parameter.
   • Other applicable keys available to the application.
   The order for collecting and trying keys from different key sources is typically application dependent. For example, frequently all keys from a one set of locations, such as local caches, will be tried before collecting and trying keys from other locations.
2. Filter the set of collected keys. For instance, some applications will use only keys referenced by kid (key ID) or x5t (X.509 certificate SHA-1 thumbprint) parameters. If the application uses the alg (algorithm), use (public key use), or key_ops (key operations) parameters, keys with keys with inappropriate values of those parameters would be excluded. Additionally, keys might be filtered to include or exclude keys with certain other member values in an application specific manner. For some applications, no filtering will be applied.
3. Order the set of collected keys. For instance, keys referenced by kid (Key ID) or x5t (X.509 Certificate SHA-1 Thumbprint) parameters might be tried before keys with neither of these values. Likewise, keys with certain member values might be ordered before keys with other member values. For some applications, no ordering will be applied.
4. Make trust decisions about the keys. Signatures made with keys not meeting the application's trust criteria would not be accepted. Such criteria might include, but is not limited to the source of the key, whether the TLS certificate validates for keys retrieved from URLs, whether a key in an X.509 certificate is backed by a valid certificate chain, and other information known by the application.
5. Attempt signature or MAC validation for a JWS object or decryption of a JWE object with some or all of the collected and possibly filtered and/or ordered keys. A limit on the number of keys to be tried might be applied. This process will normally terminate following a successful validation or decryption.

Note that it is reasonable for some applications to perform signature or MAC validation prior to making a trust decision about a key, since keys for which the validation fails need no trust decision.

Appendix E.  Negative Test Case for "crit" Header Parameter

Conforming implementations must reject input containing critical extensions that are not understood or cannot be processed. The following JWS must be rejected by all implementations, because it uses an extension Header Parameter name http://example.invalid/UNDEFINED that they do not understand. Any other similar input, in which the use of the value http://example.invalid/UNDEFINED is substituted for any other Header Parameter name not understood by the implementation, must also be rejected.

The JWS Protected Header value for this JWS is:

  {"alg":"none",
   "crit":["http://example.invalid/UNDEFINED"],
   "http://example.invalid/UNDEFINED":true
  }

The complete JWS that must be rejected is as follows (with line breaks for display purposes only):

  eyJhbGciOiJub25lIiwNCiAiY3JpdCI6WyJodHRwOi8vZXhhbXBsZS5jb20vVU5ERU
  ZJTkVEIl0sDQogImh0dHA6Ly9leGFtcGxlLmNvbS9VTkRFRklORUQiOnRydWUNCn0.
  RkFJTA.

Appendix F.  Detached Content

In some contexts, it is useful integrity protect content that is not itself contained in a JWS object. One way to do this is create a JWS object in the normal fashion using a representation of the content as the payload, but then delete the payload representation from the JWS, and send this modified object to the recipient, rather than the JWS. When using the JWS Compact Serialization, the deletion is accomplished by replacing the second field (which contains BASE64URL(JWS Payload)) value with the empty string; when using the JWS JSON Serialization, the deletion is accomplished by deleting the payload member. This method assumes that the recipient can reconstruct the exact payload used in the JWS. To use the modified object, the recipient reconstructs the JWS by re-inserting the payload representation into the modified object, and uses the resulting JWS in the usual manner. Note that this method needs no support from JWS libraries, as applications can use this method by modifying the inputs and outputs of standard JWS libraries.

Appendix G.  Acknowledgements

Solutions for signing JSON content were previously explored by Magic Signatures (Panzer (editor), J., Laurie, B., and D. Balfanz, “Magic Signatures,” January 2011.) [MagicSignatures], JSON Simple Sign (Bradley, J. and N. Sakimura (editor), “JSON Simple Sign,” September 2010.) [JSS], and Canvas Applications (Facebook, “Canvas Applications,” 2010.) [CanvasApp], all of which influenced this draft.

Thanks to Axel Nennker for his early implementation and feedback on the JWS and JWE specifications.

This specification is the work of the JOSE Working Group, which includes dozens of active and dedicated participants. In particular, the following individuals contributed ideas, feedback, and wording that influenced this specification:

Dirk Balfanz, Richard Barnes, Brian Campbell, Breno de Medeiros, Dick Hardt, Joe Hildebrand, Jeff Hodges, Edmund Jay, Yaron Y. Goland, Ben Laurie, James Manger, Matt Miller, Kathleen Moriarty, Tony Nadalin, Hideki Nara, Axel Nennker, John Panzer, Emmanuel Raviart, Eric Rescorla, Jim Schaad, Paul Tarjan, Hannes Tschofenig, and Sean Turner.

Jim Schaad and Karen O'Donoghue chaired the JOSE working group and Sean Turner, Stephen Farrell, and Kathleen Moriarty served as Security area directors during the creation of this specification.

Appendix H.  Document History

[[ to be removed by the RFC Editor before publication as an RFC ]]

-32

• Addressed Gen-ART review comments by Russ Housley.
• Addressed secdir review comments by Tero Kivinen, Stephen Kent, and Scott Kelly.
• Replaced the term Plaintext JWS with Unsecured JWS.

-31

• Reworded the language about JWS implementations ignoring the typ and cty parameters, explicitly saying that their processing is performed by JWS applications.
• Added additional guidance on ciphersuites currently considered to be appropriate for use, including a reference to a recent update by the TLS working group.

-30

• Added subsection headings within the Overview section for the two serializations.
• Added references and cleaned up the reference syntax in a few places.
• Applied minor wording changes to the Security Considerations section and made other local editorial improvements.

-29

• Replaced the terms JWS Header, JWE Header, and JWT Header with a single JOSE Header term defined in the JWS specification. This also enabled a single Header Parameter definition to be used and reduced other areas of duplication between specifications.

-28

• Revised the introduction to the Security Considerations section. Also introduced additional subsection headings for security considerations items and also moved a security consideration item here from the JWA draft.
• Added text about when applications typically would and would not use typ and cty header parameters.

-27

• Added the x5t#S256 (X.509 Certificate SHA-256 Thumbprint) header parameter.
• Stated that any JSON inputs not conforming to the JSON-text syntax defined in RFC 7159 input MUST be rejected in their entirety.
• Simplified the TLS requirements.

-26

• Referenced Section 6 of RFC 6125 for TLS server certificate identity validation.
• Described potential sources of ambiguity in representing the JSON objects used in the examples. The octets of the actual UTF-8 representations of the JSON objects used in the examples are included to remove these ambiguities.
• Added a small amount of additional explanatory text to the signature validation examples to aid implementers.
• Noted that octet sequences are depicted using JSON array notation.
• Updated references, including to W3C specifications.

-25

• No changes were made, other than to the version number and date.

-24

• Updated the JSON reference to RFC 7159.

-23

• Clarified that the base64url encoding includes no line breaks, white space, or other additional characters.

-22

• Corrected RFC 2119 terminology usage.
• Replaced references to draft-ietf-json-rfc4627bis with RFC 7158.

-21

• Applied review comments to the appendix "Notes on Key Selection", addressing issue #93.
• Changed some references from being normative to informative, addressing issue #90.
• Applied review comments to the JSON Serialization section, addressing issue #121.

-20

• Made terminology definitions more consistent, addressing issue #165.
• Restructured the JSON Serialization section to call out the parameters used in hanging lists, addressing issue #121.
• Described key filtering and refined other aspects of the text in the appendix "Notes on Key Selection", addressing issue #93.
• Replaced references to RFC 4627 with draft-ietf-json-rfc4627bis, addressing issue #90.

-19

• Added the appendix "Notes on Validation Key Selection", addressing issue #93.
• Reordered the key selection parameters.

-18

• Updated the mandatory-to-implement (MTI) language to say that applications using this specification need to specify what serialization and serialization features are used for that application, addressing issue #119.
• Changes to address editorial and minor issues #25, #89, #97, #110, #114, #115, #116, #117, #120, and #184.
• Added and used Header Parameter Description registry field.

-17

• Refined the typ and cty definitions to always be MIME Media Types, with the omission of "application/" prefixes recommended for brevity, addressing issue #50.
• Updated the mandatory-to-implement (MTI) language to say that general-purpose implementations must implement the single signature/MAC value case for both serializations whereas special-purpose implementations can implement just one serialization if that meets the needs of the use cases the implementation is designed for, addressing issue #119.
• Explicitly named all the logical components of a JWS and defined the processing rules and serializations in terms of those components, addressing issues #60, #61, and #62.
• Replaced verbose repetitive phases such as "base64url encode the octets of the UTF-8 representation of X" with mathematical notation such as "BASE64URL(UTF8(X))".
• Terms used in multiple documents are now defined in one place and incorporated by reference. Some lightly used or obvious terms were also removed. This addresses issue #58.

-16

• Changes to address editorial and minor issues #50, #98, #99, #102, #104, #106, #107, #111, and #112.

-15

• Clarified that it is an application decision which signatures, MACs, or plaintext values must successfully validate for the JWS to be accepted, addressing issue #35.
• Corrected editorial error in ES512 example.
• Changes to address editorial and minor issues #34, #96, #100, #101, #104, #105, and #106.

-14

• Stated that the signature parameter is to be omitted in the JWS JSON Serialization when its value would be empty (which is only the case for a Plaintext JWS).

-13

• Made all header parameter values be per-signature/MAC, addressing issue #24.

-12

• Clarified that the typ and cty header parameters are used in an application-specific manner and have no effect upon the JWS processing.
• Replaced the MIME types application/jws+json and application/jws with application/jose+json and application/jose.
• Stated that recipients MUST either reject JWSs with duplicate Header Parameter Names or use a JSON parser that returns only the lexically last duplicate member name.
• Added a Serializations section with parallel treatment of the JWS Compact Serialization and the JWS JSON Serialization and also moved the former Implementation Considerations content there.

-11

• Added Key Identification section.
• For the JWS JSON Serialization, enable header parameter values to be specified in any of three parameters: the protected member that is integrity protected and shared among all recipients, the unprotected member that is not integrity protected and shared among all recipients, and the header member that is not integrity protected and specific to a particular recipient. (This does not affect the JWS Compact Serialization, in which all header parameter values are in a single integrity protected JWE Header value.)
• Removed suggested compact serialization for multiple digital signatures and/or MACs.
• Changed the MIME type name application/jws-js to application/jws+json, addressing issue #22.
• Tightened the description of the crit (critical) header parameter.
• Added a negative test case for the crit header parameter

-10

• Added an appendix suggesting a possible compact serialization for JWSs with multiple digital signatures and/or MACs.

-09

• Added JWS JSON Serialization, as specified by draft-jones-jose-jws-json-serialization-04.
• Registered application/jws-js MIME type and JWS-JS typ header parameter value.
• Defined that the default action for header parameters that are not understood is to ignore them unless specifically designated as "MUST be understood" or included in the new crit (critical) header parameter list. This addressed issue #6.
• Changed term "JWS Secured Input" to "JWS Signing Input".
• Changed from using the term "byte" to "octet" when referring to 8 bit values.
• Changed member name from recipients to signatures in the JWS JSON Serialization.
• Added complete values using the JWS Compact Serialization for all examples.

-08

• Applied editorial improvements suggested by Jeff Hodges and Hannes Tschofenig. Many of these simplified the terminology used.
• Clarified statements of the form "This header parameter is OPTIONAL" to "Use of this header parameter is OPTIONAL".
• Added a Header Parameter Usage Location(s) field to the IANA JSON Web Signature and Encryption Header Parameters registry.
• Added seriesInfo information to Internet Draft references.

-07

• Updated references.

-06

• Changed x5c (X.509 Certificate Chain) representation from being a single string to being an array of strings, each containing a single base64 encoded DER certificate value, representing elements of the certificate chain.
• Applied changes made by the RFC Editor to RFC 6749's registry language to this specification.

-05

• Added statement that "StringOrURI values are compared as case-sensitive strings with no transformations or canonicalizations applied".
• Indented artwork elements to better distinguish them from the body text.

-04

• Completed JSON Security Considerations section, including considerations about rejecting input with duplicate member names.
• Completed security considerations on the use of a SHA-1 hash when computing x5t (x.509 certificate thumbprint) values.
• Refer to the registries as the primary sources of defined values and then secondarily reference the sections defining the initial contents of the registries.
• Normatively reference XML DSIG 2.0 for its security considerations.
• Added this language to Registration Templates: "This name is case sensitive. Names that match other registered names in a case insensitive manner SHOULD NOT be accepted."
• Reference draft-jones-jose-jws-json-serialization instead of draft-jones-json-web-signature-json-serialization.
• Described additional open issues.
• Applied editorial suggestions.

-03

• Added the cty (content type) header parameter for declaring type information about the secured content, as opposed to the typ (type) header parameter, which declares type information about this object.
• Added "Collision Resistant Namespace" to the terminology section.
• Reference ITU.X690.1994 for DER encoding.
• Added an example JWS using ECDSA P-521 SHA-512. This has particular illustrative value because of the use of the 521 bit integers in the key and signature values. This is also an example in which the payload is not a base64url encoded JSON object.
• Added an example x5c value.
• No longer say "the UTF-8 representation of the JWS Secured Input (which is the same as the ASCII representation)". Just call it "the ASCII representation of the JWS Secured Input".
• Added Registration Template sections for defined registries.
• Added Registry Contents sections to populate registry values.
• Changed name of the JSON Web Signature and Encryption "typ" Values registry to be the JSON Web Signature and Encryption Type Values registry, since it is used for more than just values of the typ parameter.
• Moved registries JSON Web Signature and Encryption Header Parameters and JSON Web Signature and Encryption Type Values to the JWS specification.
• Numerous editorial improvements.

-02

• Clarified that it is an error when a kid value is included and no matching key is found.
• Removed assumption that kid (key ID) can only refer to an asymmetric key.
• Clarified that JWSs with duplicate Header Parameter Names MUST be rejected.
• Clarified the relationship between typ header parameter values and MIME types.
• Registered application/jws MIME type and "JWS" typ header parameter value.
• Simplified JWK terminology to get replace the "JWK Key Object" and "JWK Container Object" terms with simply "JSON Web Key (JWK)" and "JSON Web Key Set (JWK Set)" and to eliminate potential confusion between single keys and sets of keys. As part of this change, the Header Parameter Name for a public key value was changed from jpk (JSON Public Key) to jwk (JSON Web Key).
• Added suggestion on defining additional header parameters such as x5t#S256 in the future for certificate thumbprints using hash algorithms other than SHA-1.
• Specify RFC 2818 server identity validation, rather than RFC 6125 (paralleling the same decision in the OAuth specs).
• Generalized language to refer to Message Authentication Codes (MACs) rather than Hash-based Message Authentication Codes (HMACs) unless in a context specific to HMAC algorithms.
• Reformatted to give each header parameter its own section heading.

-01

• Moved definition of Plaintext JWSs (using "alg":"none") here from the JWT specification since this functionality is likely to be useful in more contexts that just for JWTs.
• Added jpk and x5c header parameters for including JWK public keys and X.509 certificate chains directly in the header.
• Clarified that this specification is defining the JWS Compact Serialization. Referenced the new JWS-JS spec, which defines the JWS JSON Serialization.
• Added text "New header parameters should be introduced sparingly since an implementation that does not understand a parameter MUST reject the JWS".
• Clarified that the order of the creation and validation steps is not significant in cases where there are no dependencies between the inputs and outputs of the steps.
• Changed "no canonicalization is performed" to "no canonicalization need be performed".
• Corrected the Magic Signatures reference.
• Made other editorial improvements suggested by JOSE working group participants.

-00

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

Authors' Addresses