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Versions: 00 draft-ietf-jose-jws-signing-input-options

JOSE Working Group                                              M. Jones
Internet-Draft                                                 Microsoft
Intended status: Standards Track                            May 27, 2015
Expires: November 28, 2015


                       JWS Signing Input Options
             draft-jones-jose-jws-signing-input-options-00

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.

   Also, JWS includes a representation of the JWS Protected Header and a
   period ('.') character in the JWS Signature computation.  While this
   cryptographically binds the protected Header Parameters to the
   integrity protected payload, some of have described use cases in
   which this binding 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
   include a representation of the JWS Protected Header and a period
   ('.') character in the JWS Signing Input.

   These options are intended to broaden the set of use cases for which
   the use of JWS is a good fit.

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



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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 28, 2015.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Notational Conventions . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Header Parameters Defined  . . . . . . . . . . . . . . . . . .  5
   4.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Example with {"alg":"HS256"} . . . . . . . . . . . . . . .  7
     4.2.  Example with {"alg":"HS256","sph":false} . . . . . . . . .  7
     4.3.  Example with {"alg":"HS256","b64":false} . . . . . . . . .  7
     4.4.  Example with {"alg":"HS256","sph":false,"b64":false} . . .  8
   5.  Intended Use by Applications . . . . . . . . . . . . . . . . .  8
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
     6.1.  JWS and JWE Header Parameter Registration  . . . . . . . .  8
       6.1.1.  Registry Contents  . . . . . . . . . . . . . . . . . .  8
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
     7.1.  Unsecured Header Parameters  . . . . . . . . . . . . . . .  9
     7.2.  Unencoded Payloads . . . . . . . . . . . . . . . . . . . .  9
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     8.1.  Normative References . . . . . . . . . . . . . . . . . . .  9
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 10
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 10
   Appendix B.  Document History  . . . . . . . . . . . . . . . . . . 11
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11



























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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 either
   the base64url encoding of the payload or the addition of information
   beyond the payload itself to the JWS Signing Input present a burden
   to implementation and adoption, particularly when the payload is
   large and/or detached.

   This specification introduces two new JWS Header Parameter values
   that generalize the JWS Signing Input computation in a manner that
   makes these two behaviors selectable and optional.

   The primary set of use cases where these enhancements 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
   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.

   The advantages of not having to add a representation of the JWS
   Protected Header and a period ('.') character as a prefix to the
   payload representation in JWS Signing Input are similar.  If the
   prefix is present in the JWS Signing Input, then space has to be
   allocated to hold the JWS Signing Input that includes a copy of the
   (large) payload representation.  This is necessary because most
   cryptographic libraries underlying the JWS implementation will
   require that the JWS Signing Input be represented as a contiguous
   octet sequence.

   In summary, these options 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 document are to be interpreted as described in



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   "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.

   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.

   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.  Header Parameters Defined

   [JWS] defines the JWS Signing Input value to be
   ASCII(BASE64URL(UTF8(JWS Protected Header)) || '.' || BASE64URL(JWS
   Payload)).  The following Header Parameters are defined that modify
   the JWS Signing Input computation in the following ways:

   sph
      The "sph" (secure protected header) Header Parameter determines
      whether the octet sequence ASCII(BASE64URL(UTF8(JWS Protected
      Header)) || '.') is included in the JWS Signing Input or not.
      When the "sph" value is "false", it is not included.  The "sph"
      value is a JSON [RFC7159] boolean, with a default value of "true".

   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 payload 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".  Note
      that unless the payload is detached, as described in Appendix F of
      [JWS], many payload values (such as those including period ('.')
      characters) would cause errors parsing the resulting JWSs,
      depending upon the serialization used.  See Section 7.2 for



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      limitations on using unencoded payloads.

   The following table shows the JWS Signing Input computation,
   depending upon the values of these parameters:

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


4.  Examples

   This section gives some examples of possible uses of these Header
   Parameters and resulting JWSs using the JWS Compact Serialization.
   All these examples use the JWS Payload value [36, 46, 48, 50].  This
   octet sequence represents the ASCII characters "$.02".  Its
   base64url-encoded representation is "JC4wMg".

   The following table shows different sets of Header Parameter values
   and the resulting JWS Signing Input values represented as ASCII
   characters:

   +--------------------------------+----------------------------------+
   | JWS Protected Header           | JWS Signing Input Value          |
   +--------------------------------+----------------------------------+
   | {"alg":"HS256"}                | eyJhbGciOiJIUzI1NiJ9.JC4wMg      |
   | {"alg":"HS256","sph":false}    | JC4wMg                           |
   | {"alg":"HS256","b64":false}    | eyJhbGciOiJIUzI1NiIsImI2NCI6ZmFs |
   |                                | c2V9.$.02                        |
   | {"alg":"HS256","sph":false,"b6 | $.02                             |
   | 4":false}                      |                                  |
   +--------------------------------+----------------------------------+

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

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



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   The rest of this section shows complete representations using the JWS
   Compact Serialization for the four JWSs with the sets of Header
   Parameters listed above.

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

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

     eyJhbGciOiJIUzI1NiJ9
     .
     JC4wMg
     .
     5mvfOroL-g7HyqJoozehmsaqmvTYGEq5jTI1gVvoEoQ

   Note that this JWS uses only features defined by [JWS] and uses
   neither of the new Header Parameters defined in Section 3.  It is the
   "control", so that differences from it when the new Header Parameters
   are used can be easily seen.

4.2.  Example with {"alg":"HS256","sph":false}

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

     eyJhbGciOiJIUzI1NiIsInNwaCI6ZmFsc2V9
     .
     JC4wMg
     .
     ojui4Wd9BM62Ag1zcfUAPHZGj_nWl2oHEJN1QIVH4IM

4.3.  Example with {"alg":"HS256","b64":false}

   The complete JWS representation for this example using the JWS
   Compact Serialization (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.



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4.4.  Example with {"alg":"HS256","sph":false,"b64":false}

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

     eyJhbGciOiJIUzI1NiIsInNwaCI6ZmFsc2UsImI2NCI6ZmFsc2V9
     .
     .
     diN05PDK8714HY7InlOPYcJ8dIBpr-JVNA_20hkfnSc

   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.


5.  Intended Use by Applications

   It is intended that application profiles specify up front whether the
   "sph" and/or "b64" are to be used by the application, with them then
   being consistently applied in the application context.  For instance,
   an application using potentially large detached payloads might
   specify that both "sph" and "b64" always be used.  Another
   application that always uses alphanumeric payloads might specify that
   "b64" always be used.  It is not intended that these parameter values
   be dynamically varied with different payloads for the same
   application.


6.  IANA Considerations

6.1.  JWS and JWE Header Parameter Registration

   This specification registers the "mac" (MAC algorithm) Header
   Parameter defined in Section 3 in the IANA JSON Web Signature and
   Encryption Header Parameters registry defined in [JWS].

6.1.1.  Registry Contents

   o  Header Parameter Name: "sph"
   o  Header Parameter Description: Secure Protected Header
   o  Header Parameter Usage Location(s): JWS
   o  Change Controller: IETF
   o  Specification Document(s): Section 3 of [[ this document ]]






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


7.  Security Considerations

7.1.  Unsecured Header Parameters

   The same security considerations apply to the case when the "sph"
   (secure protected header) value is "false" as apply when Header
   Parameters are carried in the JWS Unprotected Header.  These are
   described in Section 10.7 of [JWS].

7.2.  Unencoded Payloads

   [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.
   This encoding also intentionally excludes characters whose
   representations may require escaping in some contexts and excludes
   whitespace and line breaks, as all of these can result in changes to
   the payload during transmission.

   When the "b64" (secure protected header) 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 and that the
   payload will not be modified during transmission.  For instance, this
   means that payloads cannot contain period ('.') characters when using
   the JWS Compact Serialization, unless the payload is detached.
   Similarly, if the JWS 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 ('~'), unless it is
   detached.


8.  References

8.1.  Normative References

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



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

   [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, March 1997.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [RFC7159]  Bray, T., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, March 2014.

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

8.2.  Informative References

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

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              February 1997.

   [RFC3447]  Jonsson, J. and B. Kaliski, "Public-Key Cryptography
              Standards (PKCS) #1: RSA Cryptography Specifications
              Version 2.1", RFC 3447, February 2003.

   [SHS]      National Institute of Standards and Technology, "Secure
              Hash Standard (SHS)", FIPS PUB 180-4, March 2012, <http://
              csrc.nist.gov/publications/fips/fips180-4/fips-180-4.pdf>.


Appendix A.  Acknowledgements

   Anders Rundgren, Richard Barnes, Phillip Hallam-Baker, Jim Schaad,
   Matt Miller, Martin Thomson, and others have all made the case at
   different times for using a representation of the payload that is not
   base64url-encoded and/or not cryptographically binding the Header
   Parameter values to the integrity protected payload in contexts in
   which it safe to do so.





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Appendix B.  Document History

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

   -00

   o  Created draft-jones-jose-jws-signing-input-options.


Author's Address

   Michael B. Jones
   Microsoft

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



































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