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Versions: 00 01

Network Working Group                                           J. Benet
Internet-Draft                                             Protocol Labs
Intended status: Standards Track                               M. Sporny
Expires: July 1, 2019                                     Digital Bazaar
                                                       December 28, 2018


                       The Multibase Data Format
                    draft-multiformats-multibase-00

Abstract

   Raw binary data is often encoded using a mechanism that enables the
   data to be included in human-readable text-based formats.  This
   mechanism is often referred to as "base-encoding the data".  Base-
   encoding is often used when expressing binary data in hyperlinks,
   cryptographic keys in web pages, or security tokens in application
   software.  There are a variety of base-encodings, such as base32,
   base58, and base64.  It is not always possible to differentiate one
   base-encoding from another.  The purpose of this specification is to
   provide a mechanism to be able to deterministically identify the
   base-encoding for a particular string of data.

Feedback

   This specification is a joint work product of Protocol Labs [1], the
   W3C Digital Verification Community Group [2], and the W3C Credentials
   Community Group [3].  Feedback related to this specification should
   logged in the issue tracker [4] or be sent to public-
   credentials@w3.org [5].  .

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 July 1, 2019.




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Copyright Notice

   Copyright (c) 2018 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  The Multibase Format  . . . . . . . . . . . . . . . . . . . .   3
     2.1.  A Multibase Example . . . . . . . . . . . . . . . . . . .   3
   3.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Normative References  . . . . . . . . . . . . . . . . . .   3
     3.2.  Informative References  . . . . . . . . . . . . . . . . .   4
     3.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   Appendix A.  Security Considerations  . . . . . . . . . . . . . .   4
   Appendix B.  Test Values  . . . . . . . . . . . . . . . . . . . .   4
     B.1.  Hexadecimal upper-case encoding . . . . . . . . . . . . .   5
     B.2.  Base-32 upper-case encoding, no padding . . . . . . . . .   5
     B.3.  Base-58 Bitcoin encoding  . . . . . . . . . . . . . . . .   5
     B.4.  Base-64 with padding and MIME-encoding  . . . . . . . . .   5
   Appendix C.  Acknowledgements . . . . . . . . . . . . . . . . . .   5
   Appendix D.  IANA Considerations  . . . . . . . . . . . . . . . .   5
     D.1.  The Multibase Algorithms Registry . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   This specification describes a forward-compatible data model for
   expressing raw binary data in a variety of base-encoding formats such
   as base32, base58. and base64.

   When text is encoded as bytes, we can usually use a one-size-fits-all
   encoding (UTF-8) because we're always encoding to the same set of 256
   bytes.  When that doesn't work, usually for historical or performance
   reasons, we can usually infer the encoding from the context.

   However, when bytes are encoded as text (using a base encoding), the
   choice of base encoding is often restricted by the context.  Worse,
   these restrictions can change based on where the data appears in the
   text.  In some cases, we can only use [a-z0-9].  In others, we can
   use a larger set of characters but need a compact encoding.  This has



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   lead to a large set of "base encodings", one for every use-case.
   Unlike when encoding text to bytes, we can't just standardize around
   a single base encoding because there is no optimal encoding for all
   cases.

   Unfortunately, it's not always clear what base encoding is used;
   that's where this specification comes in.  It answers the question:

   Given data 'd' encoded into text 's', what base is it encoded with?

2.  The Multibase Format

   A multibase-encoded value follows a simple format:

   base-encoding-character base-encoded-data

   The encoding algorithm is a single character value that is always the
   first byte of the data.  The possible values for this field are
   provided in The Multibase Algorithm Registry [6].

2.1.  A Multibase Example

   The following is an encoding of "Hello World!" using the version of
   base-58 that utilizes the Bitcoin encoding character set:

   z2NEpo7TZRRrLZSi2U

   The first byte (z) specifies the multibase encoding algorithm.  The
   rest of the data specifies the value of the output of the multibase
   encoding algorithm.

3.  References

3.1.  Normative References

   [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>.

   [RFC6234]  Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234,
              DOI 10.17487/RFC6234, May 2011,
              <https://www.rfc-editor.org/info/rfc6234>.







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   [RFC7693]  Saarinen, M-J., Ed. and J-P. Aumasson, "The BLAKE2
              Cryptographic Hash and Message Authentication Code (MAC)",
              RFC 7693, DOI 10.17487/RFC7693, November 2015,
              <https://www.rfc-editor.org/info/rfc7693>.

3.2.  Informative References

   [RFC6150]  Turner, S. and L. Chen, "MD4 to Historic Status",
              RFC 6150, DOI 10.17487/RFC6150, March 2011,
              <https://www.rfc-editor.org/info/rfc6150>.

   [RFC6151]  Turner, S. and L. Chen, "Updated Security Considerations
              for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
              RFC 6151, DOI 10.17487/RFC6151, March 2011,
              <https://www.rfc-editor.org/info/rfc6151>.

3.3.  URIs

   [1] https://protocol.ai/

   [2] https://w3c-dvcg.github.io/

   [3] https://w3c-ccg.github.io/

   [4] https://github.com/w3c-dvcg/multibase/issues

   [5] mailto:public-credentials@w3.org

   [6] #mb-registry

   [7] http://www.iana.org/assignments/multibase-algorithms

   [8] https://github.com/multiformats/multibase/blob/master/
       multibase.csv

Appendix A.  Security Considerations

   There are a number of security considerations to take into account
   when implementing or utilizing this specification.  TBD

Appendix B.  Test Values

   The multibase examples are chosen to show different encoding
   algorithms and different output lengths at play.  The input test data
   for all of the examples in this section is:






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B.1.  Hexadecimal upper-case encoding

B.2.  Base-32 upper-case encoding, no padding

B.3.  Base-58 Bitcoin encoding

B.4.  Base-64 with padding and MIME-encoding

Appendix C.  Acknowledgements

   The editors would like to thank the following individuals for
   feedback on and implementations of the specification (in alphabetical
   order):

Appendix D.  IANA Considerations

D.1.  The Multibase Algorithms Registry

   The following initial entries should be added to the Multibase
   Algorithms Registry to be created and maintained at (the suggested
   URI) http://www.iana.org/assignments/multibase-algorithms [7]:






























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   +-------------------+-------------+--------+------------------------+
   |     Algorithm     |  Identifier | Status |     Specification      |
   |                   | (character) |        |                        |
   +-------------------+-------------+--------+------------------------+
   |      identity     |     0x00    | active | 8-bit binary (encoder  |
   |                   |             |        | and decoder keeps data |
   |                   |             |        |      unmodified)       |
   |       base1       |      1      | active |     unary (11111)      |
   |       base2       |      0      | active |   binary (01010101)    |
   |       base8       |      7      | active |         octal          |
   |       base10      |      9      | active |        decimal         |
   |       base16      |      f      | active |      hexadecimal       |
   |    base16upper    |      F      | active |      hexadecimal       |
   |     base32hex     |      v      | active | RFC 4648 [RFC4648] no  |
   |                   |             |        | padding - highest char |
   |   base32hexupper  |      V      | active | RFC 4648 [RFC4648] no  |
   |                   |             |        | padding - highest char |
   |    base32hexpad   |      t      | active |   RFC 4648 [RFC4648]   |
   |                   |             |        |      with padding      |
   | base32hexpadupper |      T      | active |   RFC 4648 [RFC4648]   |
   |                   |             |        |      with padding      |
   |       base32      |      b      | active | RFC 4648 [RFC4648] no  |
   |                   |             |        |        padding         |
   |    base32upper    |      B      | active | RFC 4648 [RFC4648] no  |
   |                   |             |        |        padding         |
   |     base32pad     |      c      | active |   RFC 4648 [RFC4648]   |
   |                   |             |        |      with padding      |
   |   base32padupper  |      C      | active |   RFC 4648 [RFC4648]   |
   |                   |             |        |      with padding      |
   |      base32z      |      h      | active |   z-base-32 (used by   |
   |                   |             |        |      Tahoe-LAFS)       |
   |    base58flickr   |      Z      | active |     base58 flicker     |
   |     base58btc     |      z      | active |     base58 bitcoin     |
   |       base64      |      m      | active | RFC 4648 [RFC4648] no  |
   |                   |             |        |        padding         |
   |     base64pad     |      M      | active |   RFC 4648 [RFC4648]   |
   |                   |             |        |  with padding - MIME   |
   |                   |             |        |        encoding        |
   |     base64url     |      u      | active | RFC 4648 [RFC4648] no  |
   |                   |             |        |        padding         |
   |    base64urlpad   |      U      | active |   RFC 4648 [RFC4648]   |
   |                   |             |        |      with padding      |
   +-------------------+-------------+--------+------------------------+

                  Table 1: Multihash Algorithms Registry






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   NOTE: The most up to date place for developers to find the table
   above is https://github.com/multiformats/multibase/blob/master/
   multibase.csv [8].

Authors' Addresses

   Juan Benet
   Protocol Labs
   548 Market Street, #51207
   San Francisco, CA  94104
   US

   Phone: +1 619 957 7606
   Email: juan@protocol.ai
   URI:   http://juan.benet.ai/


   Manu Sporny
   Digital Bazaar
   203 Roanoke Street W.
   Blacksburg, VA  24060
   US

   Phone: +1 540 961 4469
   Email: msporny@digitalbazaar.com
   URI:   http://manu.sporny.org/

























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