The "id-" prefix for Digest Algorithms
draft-polli-id-digest-algorithms-01

Document Type Active Internet-Draft (individual)
Author Roberto Polli 
Last updated 2020-12-18
Stream (None)
Intended RFC status (None)
Formats plain text html xml pdf htmlized (tools) htmlized bibtex
Stream Stream state (No stream defined)
Consensus Boilerplate Unknown
RFC Editor Note (None)
IESG IESG state I-D Exists
Telechat date
Responsible AD (None)
Send notices to (None)
Network Working Group                                           R. Polli
Internet-Draft     Digital Transformation Department, Italian Government
Intended status: Standards Track                        18 December 2020
Expires: 21 June 2021

                 The "id-" prefix for Digest Algorithms
                  draft-polli-id-digest-algorithms-01

Abstract

   This document defines the "id-" prefix for digest-algorithms used in
   the Digest HTTP field.  This prefix explicits that the value of the
   digest-algorithm is independent from Content-Encoding.

Note to Readers

   _RFC EDITOR: please remove this section before publication_

   Discussion of this draft takes place on the HTTP working group
   mailing list (ietf-http-wg@w3.org), which is archived at
   https://lists.w3.org/Archives/Public/ietf-http-wg/
   (https://lists.w3.org/Archives/Public/ietf-http-wg/).

   The source code and issues list for this draft can be found at
   https://github.com/ioggstream/draft-polli-Retry-Scope
   (https://github.com/ioggstream/draft-polli-Retry-Scope).

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 https://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 21 June 2021.

Polli                     Expires 21 June 2021                  [Page 1]
Internet-Draft   The "id-" prefix for Digest Algorithms    December 2020

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  The "id-" prefix for digest-algorithms  . . . . . . . . . . .   3
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
     3.1.  Disclosure of encrypted content . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  TBD how to reserve "id-" prefix?  . . . . . . . . . . . .   4
   5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  The id-crc32c digest-algorithm  . . . . . . . . . . . . .   4
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   5
   FAQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   Code Samples  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   Change Log  . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   The [DIGEST] defines a way to convey a checksum of a representation-
   data as specified in [SEMANTICS].

   As the representation data depends on the value of "Content-
   Encoding", it is useful to convey the checksum value of a
   representation without any content-coding applied.

   This proposal introduces the "id-" prefix to specify that the
   provided digest-algorithm value is computed on the representation-
   data without any content-coding applied.

Polli                     Expires 21 June 2021                  [Page 2]
Internet-Draft   The "id-" prefix for Digest Algorithms    December 2020

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
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.  These words may also appear in this
   document in lower case as plain English words, absent their normative
   meanings.

   This document uses the Augmented BNF defined in [RFC5234] and updated
   by [RFC7405].

   The definitions "representation", "selected representation",
   "representation data", "representation metadata", and "payload body"
   in this document are to be interpreted as described in [SEMANTICS].

   The definitions "digest-algorithm" and "representation-data-digest"
   in this document are to be interpreted as described in [DIGEST].

2.  The "id-" prefix for digest-algorithms

   A digest-algorithm to be registered within the HTTP Digest Algorithm
   Values (https://www.iana.org/assignments/http-dig-alg/http-dig-
   alg.xhtml) MUST NOT start with the string "id-".

   The following two examples show two digest-algorithm names that
   cannot be registered

      id-crc32c
      id-adler32

   For every digest-algorithm registered in the HTTP Digest Algorithm
   Values (https://www.iana.org/assignments/http-dig-alg/http-dig-
   alg.xhtml) the associate "id-" digest-algorithm has the following
   properties:

   *  the checksum is computed on the representation-data of the
      resource when no content coding is applied;

   *  the checksum is computed according to the original digest-
      algorithm Description field, and uses the same encoding of the
      original digest-algorithm.

   This definition is compatible, and thus extends, the definition of
   the "id-sha-256" and "id-sha-512" digest-algorithms contained in
   Section X of [DIGEST].

Polli                     Expires 21 June 2021                  [Page 3]
Internet-Draft   The "id-" prefix for Digest Algorithms    December 2020

3.  Security Considerations

3.1.  Disclosure of encrypted content

   Like the "id-sha-256" digest-algoritm defined in [DIGEST] if the
   content-coding provides encryption features, sending the checksum of
   unencoded representation can disclose information.

4.  IANA Considerations

4.1.  TBD how to reserve "id-" prefix?

5.  Examples

5.1.  The id-crc32c digest-algorithm

   The following request conveys a brotli encoded json object

   {"hello": "world"}

   The "Digest" computed using the "crc32c" digest-algorithm present in
   HTTP Digest Algorithm Values (https://www.iana.org/assignments/http-
   dig-alg/http-dig-alg.xhtml) is content-coding aware, while its
   associated "id-" digest-algorithm is not "id-crc32c"

   POST /data HTTP/1.1
   Content-Type: application/json
   Content-Encoding: br
   Digest: id-crc32c=43794720, crc32c=DB329237

   CwGAZG9nAw==

6.  Normative References

   [DIGEST]   Polli, R. and L. Pardue, "Digest Headers", Work in
              Progress, Internet-Draft, draft-ietf-httpbis-digest-
              headers-04, 17 October 2020, <http://www.ietf.org/
              internet-drafts/draft-ietf-httpbis-digest-headers-04.txt>.

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

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

Polli                     Expires 21 June 2021                  [Page 4]
Internet-Draft   The "id-" prefix for Digest Algorithms    December 2020

   [RFC7405]  Kyzivat, P., "Case-Sensitive String Support in ABNF",
              RFC 7405, DOI 10.17487/RFC7405, December 2014,
              <https://www.rfc-editor.org/info/rfc7405>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [SEMANTICS]
              Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,
              <https://www.rfc-editor.org/info/rfc7231>.

Appendix A.  Acknowledgements

   This specification was born from a thread created by James Manger and
   the subsequent discussion here https://github.com/httpwg/http-
   extensions/issues/885.

FAQ

   Q: Question 1  Answer 1

Code Samples

   _RFC Editor: Please remove this section before publication._

   How can I generate and validate the "Digest" values shown in the
   examples throughout this document?

   The following python3 code can be used to generate digests for json
   objects using crc32c algorithm.  Note that these are formatted as
   base64.  This function could be adapted to other algorithms and
   should take into account their specific formatting rules.

Polli                     Expires 21 June 2021                  [Page 5]
Internet-Draft   The "id-" prefix for Digest Algorithms    December 2020

   import base64, json, brotli, crc32c

   identity = lambda x: x

   def digest(item, content_coding=identity, algorithm=crc32c.crc32c):
       json_bytes = json.dumps(item).encode()
       content_encoded = content_coding(json_bytes)
       checksum = algorithm(content_encoded)
       # encode result has uppercase hex
       return hex(checksum)[2:].upper()

   item = {"hello": "world"}

   print("crc32c digest value for a br-coded representation: ",
       digest(item, content_coding=brotli.compress)
   )

   print("id-crc32c digest value for a br-coded representation: ",
       digest(item, content_coding=identity)
   )

Change Log

   RFC EDITOR PLEASE DELETE THIS SECTION.

Author's Address

   Roberto Polli
   Digital Transformation Department, Italian Government
   Italy

   Email: robipolli@gmail.com

Polli                     Expires 21 June 2021                  [Page 6]