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Versions: 00                                                            
Internet Draft                                 Edmon Chung, Neteka Inc.
<draft-ietf-idn-ace16x-00.txt>                 David Leung, Neteka Inc.
                                                              June 2001

                 ACE using Extended Hex Values (ACE16x)


   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.  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

   The reader is cautioned not to depend on the values that appear in
   examples to be current or complete, since their purpose is primarily
   educational.  Distribution of this memo is unlimited.

   The list of current Internet-Drafts can be accessed at
   The list of Internet-Draft Shadow Directories can be accessed at


   ACE16x is a simplified version of DUDE [DUDE-02] that requires no 5
   bit or base-32 mapping.  ACE16x encoding results in a string that
   performs as well as DUDE technically.

   Instead of resorting to a quartet-to-quintet mapping mechanism,
   ACE16x simply uses the hex values with an extended hex (16x) scheme
   for compression.  In essence, instead of pre-pending an extra bit,
   ACE16x shifts the last quartet of a compressed code point up to
   another character.  Additionally, the 16x value is calculable
   instead of needing to be mapped.


   The key words "MUST", "SHALL", "REQUIRED", "SHOULD", "RECOMMENDED",
   and "MAY" in this document are to be interpreted as described in RFC
   2119 [RFC2119].

   LDH: Letters, Digits and Hyphens: a string of characters that
   consists only hyphens ("-"), English letters (A-z) and digits (0-9),
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ACE16x              ACE using Extended Hex Values             June 2001

   which might not be a result of an algorithm for transcoding
   multilingual characters. For example: whatever-you-want.example

   ACE - ASCII Compatible Encoding: a string of characters resulting
   from a particular algorithm for transforming multilingual character
   information into an alphanumeric form acceptable by the existing
   DNS.  For example: bq--3bhc2zmh.tld.  In essence, ACE is a subset of

   Hexadecimal values are shown preceeded by "0x".  For example, 0x60
   is decimal 96.  As in the Unicode Standard [UNICODE], Unicode code
   points are denoted by "U+" followed by four to six hexadecimal
   digits, while a range of code points is denoted by two hexadecimal
   numbers separated by "..", with no prefixes.

Table Of Contents

   1. Introduction....................................................2
   2. Extended Hex Values (16x).......................................3
   3. Encoding Procedure..............................................3
   4. Decoding Procedure..............................................4

   5. Implementation & Examples.......................................4
   6. Key Improvements of ACE16x in comparison with DUDE-02...........6
   7. Security Considerations.........................................7
   8. References......................................................7

1. Introduction

   ACE16x is very similar to DUDE. Except that it does not require any
   base-32 mapping.

   For example, the Unicode sequence (Sections 2-4 will further discuss
   the algorithm):

      Char:      <gumi>            <kinpachi>           <sensei>
   Unicode:       U+516B              U+5148              U+751F
       Bin: 0101 0001 0110 1011 0101 0001 0100 1000 0111 0101 0001 1111
    ACE16x: 0101 0001 0101 1011           0010 0011 0010 0100 0101 0111
   (in Bin)
    ACE16x:    5    1    5    r              2    j    2    4    5    n
   (in LDH with last quartet of each code point shifted to 16x)
      DUDE:10101100011000001011          100100001110010101001010100111
   (in Bin)
      DUDE:    x    t    s    m              u    d    u    w    x    h
   (in LDH prepending 1 & 0s and mapping to base32)

Chung & Leung                                                  [Page 2]

ACE16x              ACE using Extended Hex Values             June 2001

   In brief:
       ACE16x: 515r2j245n
         DUDE: xtsmuduwxh

   Lengthwise, ACE16x is exactly the same as DUDE, while ACE16x does
   not require any 5 bit handling and mapping.  This largely simplifies
   and speeds up the process as compared with DUDE.

2. Extended Hex Values (16x)

   The extended hex (16x) values are used for the final quartet of a
   compressed code point.  This is used to preserve the reversibility
   of the encoded string, without compromising length while avoiding
   having to do a base-32 mapping.

   There are 16 characters used for hex values, the following table
   provides the extended hex (16x) values for each hex digit.

   0=0000=G   1=0001=H   2=0010=I   3=0011=J
   4=0100=K   5=0101=L   6=0110=M   7=0111=N
   8=1000=O   9=1001=P   A=1010=Q   B=1011=R
   C=1100=S   D=1101=T   E=1110=U   F=1111=V

   Note that the characters are shifted exactly 16 alphabetic positions
   from their original hex value.  Therefore no mapping is required.
   The 16x value could be calculated:

      16x value = Original hex value + 0x67 (or +0x47 for uppercase*)
           *0x67 is the code value for the lowercase letter "g".
            0x47 is the code value for the uppercase letter "G".

   Unless the "mixed-case annotation" feature is implemented, lowercase
   or uppercase form is accepted.  Since all 16x values are letters,
   for mixed-case annotations, an uppercase 16x value indicates an
   uppercase character and vice versa (Appendix B).

3. Encoding Procedure

   Similar to DUDE, all ordering of bits and quartets is big-endian
   (most significant first).

   let prev = 0x30
   for each input integer n (in order) do begin
      if n == 0x2D then output hyphen-minus
      else begin
         let diff = prev XOR n
         hex dump resulting quartets,
            as few as are sufficient (but at least one), and
            shift the last quartet to its 16x value
         let prev = n
Chung & Leung                                                  [Page 3]

ACE16x              ACE using Extended Hex Values             June 2001

   Nameprep [NAMEPREP] is not discussed in this document, but is
   expected that it be implemented for IDN.  Hence, regardless of the
   code point presented, an encoder MUST not produce an incorrect
   output.  The encoder must fail if it encounters a negative input

   The initial value used is 0x30 so that all domains beginning with a
   digit will be shorter.

4. Decoding Procedure

   let prev = 0x30
   while the input string is not exhausted do begin
      if the next character is hyphen-minus
      then consume it and output 0x2D
      else begin
         consume characters and convert them to quartets until
            encountering a 16x value
         fail upon encountering a non-ACE16x character (0-v)
            or end-of-input
         shift the 16x value back to its hex form
         concatenate the resulting quartets to form diff
         let prev = prev XOR diff
         output prev
   encode the output sequence and compare it to the input string
   fail if they do not match (case insensitively)

5. Implementation & Examples

   The following examples illustrates the similarities and
   differences between dude:

       (A) Unicode: U+0031
            ACE16x: h
              DUDE: xb

   Note that with Nameprep both should be "1" since the entire label
   consists of LDH only.  This is just to show how the initial diff
   (0x30) value affects the resulting string.

   All of the following examples are taken from the DUDE-02 draft:

       (B) Unicode: U+2C7EF U+2C7EF
            ACE16x: 2c7dvg
              DUDE: u6z2ra

       (C) Unicode: U+1752B U+1752A
            ACE16x: 1751rh
              DUDE: tzxwmb

Chung & Leung                                                  [Page 4]

ACE16x              ACE using Extended Hex Values             June 2001

       (D) Unicode: U+63AB1 U+63ABA
            ACE16x: 63a8hr
              DUDE: yv47bm

       (E) Unicode: U+261AF U+261BF
            ACE16x: 2619v1g
              DUDE: uyt6rta

       (F) Unicode: U+C3A31 U+C3A8C
            ACE16x: c3a0hbt
              DUDE: 6v4xb5p

       (G) Unicode: U+09F44 U+0954C
            ACE16x: 9f7ka0o
              DUDE: 39ue4si

       (H) Unicode: U+8D1A3 U+8C8A3
            ACE16x: 8d19j190g
              DUDE: 27t6dt3sa

       (I) Unicode: U+6C2B6 U+CC266
            ACE16x: 6c28ma00dg
              DUDE: y6u7g4ss7a

       (J) Unicode: U+002D U+002D U+002D U+E848F
            ACE16x: ---e84bv
              DUDE: ---82w8r

       (K) Unicode: U+BD08E U+002D U+002D U+002D
            ACE16x: bd0bu---
              DUDE: 57s8q---

       (L) Unicode: U+A9A24 U+002D U+002D U+002D U+C05B7
            ACE16x: a9a1k---69f9j
              DUDE: 434we---y393d

       (M) Unicode: U+7FFFFFFF
            ACE16x: 7fffffcv or explicit failure
              DUDE: z999993r or explicit failure

       (N) 3<nen>b<gumi><kinpachi><sensei>  (Latin, kanji)
           Unicode: U+0033 U+5E74 U+0062 U+7D44 U+91D1 U+516B U+5148
            ACE16x: j5e4n5e1m7d2mec9lc0bq2j245n
              DUDE: xdx8whx8tgz7ug863f6s5kuduwxh

       (O) <amuro><namie>-with-super-monkeys  (Latin, kanji, hyphens)
           Unicode: U+5B89 U+5BA4 U+5948 U+7F8E U+6075 U+002D U+0077
                    U+0069 U+0074 U+0068 U+002D U+0073 U+0075 U+0070
                    U+0065 U+0072 U+002D U+006D U+006F U+006E U+006B
                    U+0065 U+0079 U+0073
            ACE16x: 5bbp2t2es26cm1ffr-600i1u1t1s-1rml1l1n-1vihlu1sq
              DUDE: x58jupu8nuy6gt99m-yssctqtptn-tmgftfth-trcbfqtnk
Chung & Leung                                                  [Page 5]

ACE16x              ACE using Extended Hex Values             June 2001

       (P) maji<de>koi<suru>5<byou><mae>  (Latin, hiragana, kanji)
           Unicode: U+006D U+0061 U+006A U+0069 U+3067 U+006B U+006F
                    U+0069 U+3059 U+308B U+0035 U+79D2 U+524D
            ACE16x: 5tsrj300u300skm303gdi30bu79en2b9v
              DUDE: pnmdvssqvssnegvsva7cvs5qz38hu53r

       (Q) <pafii>de<runba>  (Latin, katakana)
           Unicode: U+30D1 U+30D5 U+30A3 U+30FC U+0064 U+0065 U+30EB
                    U+30F3 U+30D0
            ACE16x: 30ehk7m5v309oh308u1o2j
              DUDE: vs5bezgxrvs3ibvs2qtiud

       (R) <sono><supiido><de>  (hiragana, katakana)
           Unicode: U+305D U+306E U+30B9 U+30D4 U+30FC U+30C9 U+3067
            ACE16x: 306t3jdn6t2o3lau
              DUDE: vsvpvd7hypuivf4q

6. Key Improvements of ACE16x in comparison with DUDE-02

   - ACE16x does NOT need character mapping.  Instead it uses a
     shifting mechanism that is calculable:

          16x = Original hex + 0x67 (or +0x47 for uppercase)

   - ACE16x maintains the one pass system and utilizes XOR instead of
     masking as in DUDE-01

   - ACE16x does not employ a 5bit mechanism, therefore increases

   - The initial value is set to 0x30 so that all domains beginning
     with a digit will be shorter when encoded

   - ACE16x simply hex dumps most quartets improving process time both
     in encoding and decoding.

   - The overall process time will be reduced by means of the
         1) Hex dump verses base-32 mapping
         2) Shifting verses base-32 mapping
         3) No need to pre-pend "1" or "0" bit(during encode)
         4) No need to strip first bit (during decode)

   - ACE16x is a much more simple algorithm without compromising
     performance.  The encoding mechanism is so simple that it could
     easily be expressed in an Excel spreadsheet:
     http://www.dnsii.org/ace16x/ace16x-encode.xls (The DUDE encode
     mechanism is also represented in a separate worksheet.  It could
     be observed that ACE16x is much more simple than DUDE.)

Chung & Leung                                                  [Page 6]

ACE16x              ACE using Extended Hex Values             June 2001

7. Security Considerations

   This document does not talk about DNS security issues, and it is
   believed that the proposal does not introduce additional security
   problems not already existent and/or anticipated by adding
   multilingual characters to DNS and/or using ACE.

8. References

   [Nameprep]Paul Hoffman, IMC & VPNC & Marc Blanchet, ViaGenie,
             "Preparation of Internationalized Host Names", February
             24, 2001

   [DUDE-02] Mark Welter, Brian W. Spolarich & Adam M.
             Costello,"Differential Unicode Domain Encoding (DUDE)",
             June 7, 2001.

Appendix A. Acknowledgements

   The ACE16x draft is largely based on DUDE-02.  The authors would
   like to thank the authors of DUDE-02 Mark Welter, Brian W. Spolarich
   & Adam M. Costello for their inspiration.

Appendix B. Mixed-case annotation

   This section is taken from DUDE and modified for ACE16x

   In order to use ACE16X to represent case-insensitive Unicode
   strings, higher layers need to case-fold the Unicode strings prior
   to ACE16X encoding.  The encoded string can, however, use mixed-case
   16x as an annotation telling how to convert the folded Unicode
   string into a mixed-case Unicode string for display purposes.

   Each Unicode code point (unless it is U+002D hyphen-minus) is
   represented by a sequence of hex and 16x characters, the last of
   which is always a 16x character, which is always a letter (as
   opposed to a digit).  If that letter is uppercase, it is a
   suggestion that the Unicode character be mapped to uppercase (if
   possible); if the letter is lowercase, it is a suggestion that the
   Unicode character be mapped to lowercase (if possible).

   ACE16X encoders and decoders are not required to support these
   annotations, and higher layers need not use them.

   Example:  In order to suggest that example (O) in Section 5
   "Implementation & Examples" be displayed as:


   one could capitalize the ACE16X encoding as:

Chung & Leung                                                  [Page 7]

ACE16x              ACE using Extended Hex Values             June 2001


Edmon Chung
Neteka Inc.
2462 Yonge St. Toronto,
Ontario, Canada M4P 2H5

David Leung
Neteka Inc.
2462 Yonge St. Toronto,
Ontario, Canada M4P 2H5

Chung & Leung                                                  [Page 8]