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Versions: (draft-jones-jose-jws-signing-input-options) 00 01 02 03 04 05 06 07 08 09 RFC 7797

JOSE Working Group                                              M. Jones
Internet-Draft                                                 Microsoft
Updates: 7519 (if approved)                            November 11, 2015
Intended status: Standards Track
Expires: May 14, 2016


                      JWS Unencoded Payload Option
              draft-ietf-jose-jws-signing-input-options-04

Abstract

   JSON Web Signature (JWS) represents the payload of a JWS as a
   base64url encoded value and uses this value in the JWS Signature
   computation.  While this enables arbitrary payloads to be integrity
   protected, some have described use cases in which the base64url
   encoding is unnecessary and/or an impediment to adoption, especially
   when the payload is large and/or detached.  This specification
   defines a means of accommodating these use cases by defining an
   option to change the JWS Signing Input computation to not base64url-
   encode the payload.  This option is intended to broaden the set of
   use cases for which the use of JWS is a good fit.

   This specification updates RFC 7519 by prohibiting the use of this
   option in JSON Web Tokens (JWTs).

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 14, 2016.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Notational Conventions . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  The "b64" Header Parameter . . . . . . . . . . . . . . . . . .  4
   4.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     4.1.  Example with Header Parameters {"alg":"HS256"} . . . . . .  5
     4.2.  Example with Header Parameters
           {"alg":"HS256","b64":false}  . . . . . . . . . . . . . . .  6
   5.  Unencoded Payload Content Restrictions . . . . . . . . . . . .  6
     5.1.  Unencoded Detached Payload . . . . . . . . . . . . . . . .  7
     5.2.  Unencoded JWS Compact Serialization Payload  . . . . . . .  7
     5.3.  Unencoded JWS JSON Serialization Payload . . . . . . . . .  7
   6.  Intended Use by Applications . . . . . . . . . . . . . . . . .  8
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
     8.1.  JWS and JWE Header Parameter Registration  . . . . . . . . 10
       8.1.1.  Registry Contents  . . . . . . . . . . . . . . . . . . 10
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 11
   Appendix B.  Document History  . . . . . . . . . . . . . . . . . . 11
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12















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1.  Introduction

   The "JSON Web Signature (JWS)" [JWS] specification defines the JWS
   Signing Input as the input to the digital signature or MAC
   computation, with the value ASCII(BASE64URL(UTF8(JWS Protected
   Header)) || '.' || BASE64URL(JWS Payload)).  While this works well in
   practice for many use cases, including those accommodating arbitrary
   payload values, other use cases have been described in which
   base64url encoding the payload is unnecessary and/or an impediment to
   adoption, particularly when the payload is large and/or detached.

   This specification introduces a new JWS Header Parameter value that
   generalizes the JWS Signing Input computation in a manner that makes
   base64url encoding the payload selectable and optional.  The primary
   set of use cases where this enhancement may be helpful are those in
   which the payload may be very large and where means are already in
   place to enable the payload to be communicated between the parties
   without modifications.  Appendix F of [JWS] describes how to
   represent JWSs with detached content, which would typically be used
   for these use cases.

   The advantages of not having to base64url-encode a large payload are
   that allocation of the additional storage to hold the base64url-
   encoded form is avoided and the base64url-encoding computation never
   has to be performed.  In summary, this option can help avoid
   unnecessary copying and transformations of the potentially large
   payload, resulting in sometimes significant space and time
   improvements for deployments.

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 specification are to be interpreted as described
   in "Key words for use in RFCs to Indicate Requirement Levels"
   [RFC2119].  The interpretation should only be applied when the terms
   appear in all capital letters.

   BASE64URL(OCTETS) denotes the base64url encoding of OCTETS, per
   Section 2 of [JWS].

   UTF8(STRING) denotes the octets of the UTF-8 [RFC3629] representation
   of STRING, where STRING is a sequence of zero or more Unicode
   [UNICODE] characters.

   ASCII(STRING) denotes the octets of the ASCII [RFC20] representation
   of STRING, where STRING is a sequence of zero or more ASCII
   characters.



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


2.  Terminology

   This specification uses the same terminology as the "JSON Web
   Signature (JWS)" [JWS] and "JSON Web Algorithms (JWA)" [JWA]
   specifications.


3.  The "b64" Header Parameter

   This Header Parameter modifies the JWS Payload representation and the
   JWS Signing Input computation in the following way:

   b64
      The "b64" (base64url-encode payload) Header Parameter determines
      whether the payload is represented in the JWS and the JWS Signing
      Input as ASCII(BASE64URL(JWS Payload)) or as the JWS Payload value
      itself with no encoding performed.  When the "b64" value is
      "false", the payload is represented simply as the JWS Payload
      value; otherwise, it is represented as ASCII(BASE64URL(JWS
      Payload)).  The "b64" value is a JSON boolean, with a default
      value of "true".  When used, this Header Parameter MUST be
      integrity protected; therefore, it MUST occur only within the JWS
      Protected Header.  Use of this Header Parameter is OPTIONAL.  If
      the JWS has multiple signatures and/or MACs, the "b64" Header
      Parameter value MUST be the same for all of them.  Note that
      unless the payload is detached, many payload values would cause
      errors parsing the resulting JWSs, as described in Section 5.

   The following table shows the JWS Signing Input computation,
   depending upon the value of this parameter:

   +-------+-----------------------------------------------------------+
   | "b64" | JWS Signing Input Formula                                 |
   +-------+-----------------------------------------------------------+
   | true  | ASCII(BASE64URL(UTF8(JWS Protected Header)) || '.' ||     |
   |       | BASE64URL(JWS Payload))                                   |
   | false | ASCII(BASE64URL(UTF8(JWS Protected Header)) || '.') ||    |
   |       | JWS Payload                                               |
   +-------+-----------------------------------------------------------+


4.  Examples

   This section gives examples of JWSs showing the difference that using
   the "b64" Header Parameter makes.  The examples all use the JWS



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   Payload value [36, 46, 48, 50].  This octet sequence represents the
   ASCII characters "$.02"; its base64url-encoded representation is
   "JC4wMg".

   The following table shows a set of Header Parameter values without
   using a false "b64" Header Parameter value and a set using it, with
   the resulting JWS Signing Input values represented as ASCII
   characters:

   +-----------------------------+-------------------------------------+
   | JWS Protected Header        | JWS Signing Input Value             |
   +-----------------------------+-------------------------------------+
   | {"alg":"HS256"}             | eyJhbGciOiJIUzI1NiJ9.JC4wMg         |
   | {"alg":"HS256","b64":false} | eyJhbGciOiJIUzI1NiIsImI2NCI6ZmFsc2V |
   |                             | 9.$.02                              |
   +-----------------------------+-------------------------------------+

   These examples use the HMAC key from Appendix A.1 of [JWS], which is
   represented below as a JWK [JWK] (with line breaks within values for
   display purposes only):

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

   The rest of this section shows complete representations for the two
   JWSs above.

4.1.  Example with Header Parameters {"alg":"HS256"}

   The complete JWS representation for this example using the JWS
   Compact Serialization and a non-detached payload (with line breaks
   for display purposes only) is:

     eyJhbGciOiJIUzI1NiJ9
     .
     JC4wMg
     .
     5mvfOroL-g7HyqJoozehmsaqmvTYGEq5jTI1gVvoEoQ

   Note that this JWS uses only features defined by [JWS] and does not
   use the new "b64" Header Parameter.  It is the "control", so that
   differences when it is used can be easily seen.

   The equivalent representation for this example using the flattened
   JWS JSON Serialization is:



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     {
      "protected":
       "eyJhbGciOiJIUzI1NiJ9",
      "payload":
       "JC4wMg",
      "signature":
       "5mvfOroL-g7HyqJoozehmsaqmvTYGEq5jTI1gVvoEoQ"
     }

4.2.  Example with Header Parameters {"alg":"HS256","b64":false}

   The complete JWS representation for this example using the JWS
   Compact Serialization and a detached payload (with line breaks for
   display purposes only) is:

     eyJhbGciOiJIUzI1NiIsImI2NCI6ZmFsc2V9
     .
     .
     GsyM6AQJbQHY8aQKCbZSPJHzMRWo3HKIlcDuXof7nqs

   Note that the payload "$.02" cannot be represented in this JWS in its
   unencoded form because it contains a period ('.') character, which
   would cause parsing problems.  This JWS is therefore shown with a
   detached payload.

   The complete JWS representation for this example using the flattened
   JWS JSON Serialization and a non-detached payload is:

     {
      "protected":
       "eyJhbGciOiJIUzI1NiIsImI2NCI6ZmFsc2V9",
      "payload":
       "$.02",
      "signature":
       "GsyM6AQJbQHY8aQKCbZSPJHzMRWo3HKIlcDuXof7nqs"
     }

   If using a detached payload with the JWS JSON Serialization, the
   "payload" element would be omitted.


5.  Unencoded Payload Content Restrictions

   When the "b64" value is "false", different restrictions on the
   payload contents apply, depending upon the circumstances, as
   described in this section.  The restrictions prevent the use of
   payload values that would cause errors parsing the resulting JWSs.




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   Note that because the character sets that can be used for unencoded
   non-detached payloads differ between the two serializations, some
   JWSs using a "b64" value of "false" cannot be syntactically converted
   between the JWS JSON Serialization and the JWS Compact Serialization.
   See Section 7 for security considerations on using unencoded
   payloads.

5.1.  Unencoded Detached Payload

   Appendix F of [JWS] describes how to represent JWSs with detached
   content.  A detached payload can contain any octet sequence
   representable by the application.  The payload value will not cause
   problems parsing the JWS, since it is not represented as part of the
   JWS.  If an application uses a content encoding when representing the
   payload, then it MUST specify whether the signature or MAC is
   performed over the content-encoded representation or over the
   unencoded content.

5.2.  Unencoded JWS Compact Serialization Payload

   When using the JWS Compact Serialization, unencoded non-detached
   payloads using period ('.') characters would cause parsing errors;
   such payloads MUST NOT be used with the JWS Compact Serialization.
   Similarly, if a JWS using the JWS Compact Serialization and a non-
   detached payload is to be transmitted in a context that requires URL
   safe characters, then the application MUST ensure that the payload
   contains only the URL-safe characters 'a'-'z', 'A'-'Z', '0'-'9', dash
   ('-'), underscore ('_'), and tilde ('~').  The payload value is the
   ASCII representation of the characters in the payload string.  The
   ASCII space character and all printable ASCII characters other than
   period ('.') (those characters in the ranges %x20-2D and %x2F-7E) MAY
   be included in a non-detached payload using the JWS Compact
   Serialization, provided that the application can transmit the
   resulting JWS without modification.

   No meaning or special semantics are attached to any characters in the
   payload.  For instance, the percent ('%') character represents
   itself, and is not used by JWS objects for percent-encoding
   [RFC3986].  Applications, of course, are free to utilize content
   encoding rules of their choosing, provided that the encoded
   representations utilize only allowed payload characters.

5.3.  Unencoded JWS JSON Serialization Payload

   When using the JWS JSON Serialization, unencoded non-detached
   payloads must consist of the octets of the UTF-8 encoding of a
   sequence of Unicode code points that are representable in a JSON
   string.  The payload value is determined after performing any JSON



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   string escape processing, per Section 8.3 of RFC 7159 [RFC7159], and
   then UTF-8-encoding the resulting Unicode code points.  This means,
   for instance, that these payloads represented as JSON strings are
   equivalent ("$.02", "\u0024.02").  Unassigned Unicode code point
   values MUST NOT be used to represent the payload.


6.  Intended Use by Applications

   It is intended that application profiles specify up front whether
   "b64" with a "false" value is to be used by the application in each
   application context or not, with it then being consistently applied
   in each application context.  For instance, an application that uses
   detached payloads might specify that "b64" with a "false" value
   always be used.  It is NOT RECOMMENDED that this parameter value be
   dynamically varied with different payloads in the same application
   context.

   JSON Web Tokens (JWTs) [JWT] MUST NOT use "b64" with a "false" value.


7.  Security Considerations

   [JWS] base64url-encodes the JWS Payload to restrict the character set
   used to represent it to characters that are distinct from the
   delimiters that separate it from other JWS fields.  Those delimiters
   are the period ('.') character for the JWS Compact Serialization and
   the double-quote ('"') character for the JWS JSON Serialization.

   When the "b64" (base64url-encode payload) value is "false", these
   properties are lost.  It then becomes the responsibility of the
   application to ensure that payloads only contain characters that will
   not cause parsing problems for the serialization used, as described
   in Section 5, and that the payload will not be modified during
   transmission.

   There is no security problem if a JWS correctly created using "b64"
   with a "false" value is received by an implementation not supporting
   the "b64" Header Parameter, since the signature will fail to verify
   and the JWS will therefore be rejected.  Likewise, there is no
   security problem if a JWS is created by an implementation not
   supporting this extension and received by an implementation
   supporting it, since the JWS will not use the extension, meaning that
   the security considerations are the same as for implementations
   supporting only the functionality specified in [JWS].

   The only case in which care may need to be taken is when a JWS is
   possibly being received by a JWS implementation not supporting this



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   extension and the party producing the JWS might be an attacker that
   intentionally creates a JWS with a "b64" value of "false" but signs
   it as if its value was "true".  In this case, a JWS implementation
   not supporting this extension will accept the JWS but treat it as if
   the payload was encoded, rather than unencoded.

   While this confused case may seem like a problem that could matter,
   in fact, if the recipient trusts the creator of a JWS based on its
   signature and therefore accepts and acts upon the content in the JWS,
   yet the creator is an attacker, the recipient has much bigger
   problems than confusion between whether the payload value is encoded
   or unencoded.  In this case, the attacker can sign any payload
   whatsoever and have the recipient accept it -- including payloads
   designed to cause harm to the recipient.  If the trust established by
   verifying the signer's key does not actually establish that the
   creator is a trusted party, then this case in which JWS libraries
   supporting and not supporting the extension may respectively
   interpret the attacker's payload as being encoded or unencoded is the
   least of the application's worries.  This can only happen when the
   trust placed in the creator of the JWS is unfounded.

   The other relevant perspective on this case is that if an application
   specifies that JWSs used by it are to be created using "b64" with a
   "false" value, per Section 6, then correct implementations of that
   application must use a JWS implementation that implements this
   extension.  Thus, even malicious JWS creators intentionally
   incorrectly signing JWSs as if the "b64" value was "false" cannot
   confuse the application as to whether the payload is encoded or
   unencoded, since any incorrectly signed JWSs will be rejected due to
   the bad signature.  Only if the application is incorrectly
   implemented and doesn't support this extension when the application
   requires its use, is a problem possible.  But then again, if the
   application is incorrectly implemented, it likely has bigger problems
   than confusion about whether the payload is encoded or not.

   Only if the application dynamically switches between "false" and
   "true" values for "b64" (something NOT RECOMMENDED in Section 6),
   would it be necessary for the application to require the use of
   "crit" with a value of "["b64"]" in such application contexts.  That
   would cause even incorrectly implemented application clients that do
   not support the extension to nonetheless reject content signed using
   "b64" with a "false" value.


8.  IANA Considerations






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8.1.  JWS and JWE Header Parameter Registration

   This specification registers the "b64" Header Parameter defined in
   Section 3 in the IANA "JSON Web Signature and Encryption Header
   Parameters" registry [IANA.JOSE] established by [JWS].

8.1.1.  Registry Contents

   o  Header Parameter Name: "b64"
   o  Header Parameter Description: Base64url-Encode Payload
   o  Header Parameter Usage Location(s): JWS
   o  Change Controller: IESG
   o  Specification Document(s): Section 3 of [[ this specification ]]


9.  References

9.1.  Normative References

   [IANA.JOSE]
              IANA, "JSON Object Signing and Encryption (JOSE)",
              <http://www.iana.org/assignments/jose>.

   [JWA]      Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,
              <http://www.rfc-editor.org/info/rfc7518>.

   [JWS]      Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515,
              May 2015, <http://www.rfc-editor.org/info/rfc7515>.

   [JWT]      Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <http://www.rfc-editor.org/info/rfc7519>.

   [RFC20]    Cerf, V., "ASCII format for Network Interchange", STD 80,
              RFC 20, October 1969,
              <http://www.rfc-editor.org/info/rfc20>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
              RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, DOI 10.17487/RFC3629,
              November 2003, <http://www.rfc-editor.org/info/rfc3629>.




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   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159,
              March 2014, <http://www.rfc-editor.org/info/rfc7159>.

   [UNICODE]  The Unicode Consortium, "The Unicode Standard",
              <http://www.unicode.org/versions/latest/>.

9.2.  Informative References

   [JWK]      Jones, M., "JSON Web Key (JWK)", RFC 7517, DOI 10.17487/
              RFC7517, May 2015,
              <http://www.rfc-editor.org/info/rfc7517>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.


Appendix A.  Acknowledgements

   Anders Rundgren, Richard Barnes, Phillip Hallam-Baker, Jim Schaad,
   Matt Miller, Martin Thomson, and others have all made the case for
   being able to use a representation of the payload that is not
   base64url-encoded in contexts in which it safe to do so.

   Thanks to Sergey Beryozkin, James Manger, Axel Nennker, Anders
   Rundgren, Nat Sakimura, Jim Schaad, and Matias Woloski for their
   reviews of the specification.


Appendix B.  Document History

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

   -04

   o  Corrected a typo in the JWS JSON Serialization example.

   o  Added to the security considerations, including adding a statement
      about when "crit" should be used.

   o  Addressed the document shepherd comments.

   -03

   o  Allowed the ASCII space character and all printable ASCII
      characters other than period ('.') in non-detached unencoded



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      payloads using the JWS Compact Serialization.

   o  Updated the abstract to say that that the spec updates RFC 7519.

   o  Removed unused references.

   o  Changed the change controller to IESG.

   -02

   o  Required that "b64" be integrity protected.

   o  Stated that if the JWS has multiple signatures and/or MACs, the
      "b64" Header Parameter value MUST be the same for all of them.

   o  Stated that if applications use content encoding, they MUST
      specify whether the encoded or unencoded payload is used as the
      JWS Payload value.

   o  Reorganized the Unencoded Payload Content Restrictions section.

   o  Added an "updates" clause for RFC 7519 because this specification
      prohibits JWTs from using "b64":false.

   -01

   o  Removed the "sph" (secure protected header) Header Parameter.

   o  Changed the title to "JWS Unencoded Payload Option".

   o  Added the section "Unencoded Payload Content Restrictions".

   o  Added an example using the JWS JSON Serialization.

   -00

   o  Created the -00 JOSE working group draft from
      draft-jones-jose-jws-signing-input-options-00 with no normative
      changes.












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Author's Address

   Michael B. Jones
   Microsoft

   Email: mbj@microsoft.com
   URI:   http://self-issued.info/












































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