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The Base45 Data Encoding
draft-faltstrom-base45-01

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 9285.
Authors Patrik Fältström , Fredrik Ljunggren , Dirk-Willem van Gulik
Last updated 2021-03-11
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IESG IESG state Became RFC 9285 (Informational)
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draft-faltstrom-base45-01
Network Working Group                                       P. Faltstrom
Internet-Draft                                                    Netnod
Intended status: Standards Track                            F. Ljunggren
Expires: September 12, 2021                                        Kirei
                                                            D. van Gulik
                                                              Webweaving
                                                          March 11, 2021

                        The Base45 Data Encoding
                       draft-faltstrom-base45-01

Abstract

   This document describes the base 45 encoding scheme which is built
   upon the base 64, base 32 and base 16 encoding schemes.

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 September 12, 2021.

Copyright Notice

   Copyright (c) 2021 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
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   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.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   2
   3.  Interpretation of Encoded Data  . . . . . . . . . . . . . . .   2
   4.  The Base 45 Encoding  . . . . . . . . . . . . . . . . . . . .   2
     4.1.  Encoding example  . . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   When using QR or Aztec codes a different encoding scheme is needed
   than the already established base 64, base 32 and base 16 encoding
   schemes that are described in RFC 4648 [RFC4648].  The difference
   from those and base 45 is the key table and that the padding with '='
   is not required.

2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

3.  Interpretation of Encoded Data

   Encoded data is to be interpreted as described in RFC 4648 [RFC4648]
   with the exception that a different alphabet is selected.

4.  The Base 45 Encoding

   A 45-character subset of US-ASCII is used, the 45 characters that can
   be used in a QR or Aztec code.  If we look at Base 64, it encodes 3
   bytes in 4 characters.  Base 45 encodes 2 bytes over 3 characters.

   The two bytes [A, B] are turned into [ C, D, E] where (A*256) + B =
   (C*45*45) + (D*45) + E.  The values C, D and E are then looked up in
   Table 1 to produce a three character string and the reverse when
   decoding.

   If the number of octets are not dividable by two, the last remaining
   byte is represented by two characters.

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                  Table 1: The Base 45 Alphabet

   Value Encoding  Value Encoding  Value Encoding  Value Encoding
      00 0            12 C            24 O            36 Space
      01 1            13 D            25 P            37 $
      02 2            14 E            26 Q            38 %
      03 3            15 F            27 R            39 *
      04 4            16 G            28 S            40 +
      05 5            17 H            29 T            41 -
      06 6            18 I            30 U            42 .
      07 7            19 J            31 V            43 /
      08 8            20 K            32 W            44 :
      09 9            21 L            33 X
      10 A            22 M            34 Y
      11 B            23 N            35 Z

4.1.  Encoding example

   A series of bytes is turned into groups of two.  Each such 16 bit
   value is turned into a series of three values calculated by doing
   successive calculations modulo 45.  The values are in turned looked
   up in what is displayed in Table 1.

   Example: The string "Hello!" is the byte sequence [ 72, 101, 108,
   108, 111, 33 ].  If we look at each 16 bit value, it is [ 18633,
   27756, 28449].  When looking at the values modulo 45, we get [[ 9, 9,
   3], [ 13, 30, 36], [14, 2, 9]].  By looking up these values in the
   table we get the encoded string "993DU E29".

5.  IANA Considerations

   There are no considerations for IANA in this document.

6.  Security Considerations

   When implementing encoding and decoding it is important to be very
   careful so that buffer overflow does not take place, or anything
   similar.  This includes of course the calculations of modulo 45 and
   lookup in the table of characters.  Decoder also must be robust
   regarding input, including proper handling of the NUL character
   (ASCII 0).

   Specifically it should be noted that Base 64 (for example) pad the
   string so that the encoding has the correct number of characters.
   This is something that Base 45 does not do, i.e. Base 45 do not
   include padding.  Because of this, special care is to be taken when
   odd number of octets are to be encoded which results not in N*3

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   characters, but (N-1)*3+2 characters in the encoded string and vice
   versa, when the number of encoded characters are not divisible by 3.

7.  Acknowledgements

   The authors thank everyone that have been working with Base64 during
   the years that have proven the implementions are stable.

8.  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>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/info/rfc4648>.

Authors' Addresses

   Patrik Faltstrom
   Netnod

   Email: paf@netnod.se

   Fredrik Ljunggren
   Kirei

   Email: fredrik@kirei.se

   Dirk-Willem van Gulik
   Webweaving

   Email: dirkx@webweaving.org

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