[Docs] [txt|pdf] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: (RFC 3548) 00 01 02 03 04 RFC 4648

Network Working Group                                       S. Josefsson
Internet-Draft                                                       SJD
Obsoletes: 3548 (if approved)                               May 11, 2006
Expires: November 12, 2006


             The Base16, Base32, and Base64 Data Encodings
                     draft-josefsson-rfc3548bis-04

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   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 progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on November 12, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Keywords

   Base Encoding, Base64, Base32, Base16, Hex.

Abstract

   This document describes the commonly used base 64, base 32, and base
   16 encoding schemes.  It also discusses the use of line-feeds in
   encoded data, use of padding in encoded data, use of non-alphabet
   characters in encoded data, use of different encoding alphabets, and



Josefsson               Expires November 12, 2006               [Page 1]

Internet-Draft              Base-N encodings                    May 2006


   canonical encodings.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions Used in this Document  . . . . . . . . . . . . . .  3
   3.  Implementation Discrepancies . . . . . . . . . . . . . . . . .  3
     3.1.  Line Feeds In Encoded Data . . . . . . . . . . . . . . . .  3
     3.2.  Padding Of Encoded Data  . . . . . . . . . . . . . . . . .  4
     3.3.  Interpretation Of Non-Alphabet Characters In Encoded
           data . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.4.  Choosing The Alphabet  . . . . . . . . . . . . . . . . . .  4
     3.5.  Canonical Encoding . . . . . . . . . . . . . . . . . . . .  6
   4.  Base 64 Encoding . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Base 64 Encoding With URL And Filename Safe Alphabet . . . . .  9
   6.  Base 32 Encoding . . . . . . . . . . . . . . . . . . . . . . . 10
   7.  Base 32 Encoding With Extended Hex Alphabet  . . . . . . . . . 11
   8.  Base 16 Encoding . . . . . . . . . . . . . . . . . . . . . . . 13
   9.  Illustrations And Examples . . . . . . . . . . . . . . . . . . 14
   10. Test Vectors . . . . . . . . . . . . . . . . . . . . . . . . . 15
   11. ISO C99 Implementation Of Base64 . . . . . . . . . . . . . . . 16
     11.1. Prototypes: base64.h . . . . . . . . . . . . . . . . . . . 16
     11.2. Implementation: base64.c . . . . . . . . . . . . . . . . . 18
   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 27
   13. Changes Since RFC 3548 . . . . . . . . . . . . . . . . . . . . 27
   14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28
   15. Copying Conditions . . . . . . . . . . . . . . . . . . . . . . 28
   16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28
     16.1. Normative References . . . . . . . . . . . . . . . . . . . 28
     16.2. Informative References . . . . . . . . . . . . . . . . . . 29
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 30
   Intellectual Property and Copyright Statements . . . . . . . . . . 31


















Josefsson               Expires November 12, 2006               [Page 2]

Internet-Draft              Base-N encodings                    May 2006


1.  Introduction

   Base encoding of data is used in many situations to store or transfer
   data in environments that, perhaps for legacy reasons, are restricted
   to only US-ASCII [1] data.  Base encoding can also be used in new
   applications that do not have legacy restrictions, simply because it
   makes it possible to manipulate objects with text editors.

   In the past, different applications have had different requirements
   and thus sometimes implemented base encodings in slightly different
   ways.  Today, protocol specifications sometimes use base encodings in
   general, and "base64" in particular, without a precise description or
   reference.  Multipurpose Internet Mail Extensions (MIME) [4] is often
   used as a reference for base64 without considering the consequences
   for line-wrapping or non-alphabet characters.  The purpose of this
   specification is to establish common alphabet and encoding
   considerations.  This will hopefully reduce ambiguity in other
   documents, leading to better interoperability.


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 [2].


3.  Implementation Discrepancies

   Here we discuss the discrepancies between base encoding
   implementations in the past, and where appropriate, mandate a
   specific recommended behavior for the future.

3.1.  Line Feeds In Encoded Data

   MIME [4] is often used as a reference for base 64 encoding.  However,
   MIME does not define "base 64" per se, but rather a "base 64 Content-
   Transfer-Encoding" for use within MIME.  As such, MIME enforces a
   limit on line length of base 64 encoded data to 76 characters.  MIME
   inherits the encoding from Privacy Enhanced Mail (PEM) [3] stating it
   is "virtually identical", however PEM uses a line length of 64
   characters.  The MIME and PEM limits are both due to limits within
   SMTP.

   Implementations MUST NOT add line feeds to base encoded data unless
   the specification referring to this document explicitly directs base
   encoders to add line feeds after a specific number of characters.




Josefsson               Expires November 12, 2006               [Page 3]

Internet-Draft              Base-N encodings                    May 2006


3.2.  Padding Of Encoded Data

   In some circumstances, the use of padding ("=") in base encoded data
   is not required nor used.  In the general case, when assumptions on
   size of transported data cannot be made, padding is required to yield
   correct decoded data.

   Implementations MUST include appropriate pad characters at the end of
   encoded data unless the specification referring to this document
   explicitly states otherwise.

   The base64 and base32 alphabets use padding, as described below in
   section 4 and 6, but the base16 alphabet does not need it, see
   section 8.

3.3.  Interpretation Of Non-Alphabet Characters In Encoded data

   Base encodings use a specific, reduced, alphabet to encode binary
   data.  Non-alphabet characters could exist within base encoded data,
   caused by data corruption or by design.  Non-alphabet characters may
   be exploited as a "covert channel", where non-protocol data can be
   sent for nefarious purposes.  Non-alphabet characters might also be
   sent in order to exploit implementation errors leading to, e.g.,
   buffer overflow attacks.

   Implementations MUST reject the encoded data if it contains
   characters outside the base alphabet when interpreting base encoded
   data, unless the specification referring to this document explicitly
   states otherwise.  Such specifications may, as MIME does, instead
   state that characters outside the base encoding alphabet should
   simply be ignored when interpreting data ("be liberal in what you
   accept").  Note that this means that any adjacent carriage return/
   line feed (CRLF) characters constitute "non-alphabet characters" and
   are ignored.  Furthermore, such specifications MAY ignore the pad
   character, "=", treating it as non-alphabet data, if it is present
   before the end of the encoded data.  If more than the allowed number
   of pad characters are found at the end of the string, e.g., a base 64
   string terminated with "===", the excess pad characters MAY also be
   ignored.

3.4.  Choosing The Alphabet

   Different applications have different requirements on the characters
   in the alphabet.  Here are a few requirements that determine which
   alphabet should be used:






Josefsson               Expires November 12, 2006               [Page 4]

Internet-Draft              Base-N encodings                    May 2006


   o  Handled by humans.  Characters "0", "O" are easily confused, as
      well as "1", "l" and "I".  In the base32 alphabet below, where 0
      (zero) and 1 (one) are not present, a decoder may interpret 0 as
      O, and 1 as I or L depending on case.  (However, by default it
      should not, see previous section.)














































Josefsson               Expires November 12, 2006               [Page 5]

Internet-Draft              Base-N encodings                    May 2006


   o  Encoded into structures that mandate other requirements.  For base
      16 and base 32, this determines the use of upper- or lowercase
      alphabets.  For base 64, the non-alphanumeric characters (in
      particular "/") may be problematic in file names and URLs.

   o  Used as identifiers.  Certain characters, notably "+" and "/" in
      the base 64 alphabet, are treated as word-breaks by legacy text
      search/index tools.

   There is no universally accepted alphabet that fulfills all the
   requirements.  For an example of a highly specialized variant, see
   IMAP [8].  In this document, we document and name some currently used
   alphabets.

3.5.  Canonical Encoding

   The padding step in base 64 and base 32 encoding can, if improperly
   implemented, lead to non-significant alterations of the encoded data.
   For example, if the input is only one octet for a base 64 encoding,
   then all six bits of the first symbol are used, but only the first
   two bits of the next symbol are used.  These pad bits MUST be set to
   zero by conforming encoders, which is described in the descriptions
   on padding below.  If this property do not hold, there is no
   canonical representation of base encoded data, and multiple base
   encoded strings can be decoded to the same binary data.  If this
   property (and others discussed in this document) holds, a canonical
   encoding is guaranteed.

   In some environments, the alteration is critical and therefor
   decoders MAY chose to reject an encoding if the pad bits have not
   been set to zero.  The specification referring to this may mandate a
   specific behaviour.


4.  Base 64 Encoding

   The following description of base 64 is derived from [3], [4], [5]
   and [6].  This encoding may be referred to as "base64".

   The Base 64 encoding is designed to represent arbitrary sequences of
   octets in a form that allows the use of both upper- and lowercase
   letters but need not be humanly readable.

   A 65-character subset of US-ASCII is used, enabling 6 bits to be
   represented per printable character.  (The extra 65th character, "=",
   is used to signify a special processing function.)

   The encoding process represents 24-bit groups of input bits as output



Josefsson               Expires November 12, 2006               [Page 6]

Internet-Draft              Base-N encodings                    May 2006


   strings of 4 encoded characters.  Proceeding from left to right, a
   24-bit input group is formed by concatenating 3 8-bit input groups.
   These 24 bits are then treated as 4 concatenated 6-bit groups, each
   of which is translated into a single character in the base 64
   alphabet.

   Each 6-bit group is used as an index into an array of 64 printable
   characters.  The character referenced by the index is placed in the
   output string.

                      Table 1: The Base 64 Alphabet

     Value Encoding  Value Encoding  Value Encoding  Value Encoding
         0 A            17 R            34 i            51 z
         1 B            18 S            35 j            52 0
         2 C            19 T            36 k            53 1
         3 D            20 U            37 l            54 2
         4 E            21 V            38 m            55 3
         5 F            22 W            39 n            56 4
         6 G            23 X            40 o            57 5
         7 H            24 Y            41 p            58 6
         8 I            25 Z            42 q            59 7
         9 J            26 a            43 r            60 8
        10 K            27 b            44 s            61 9
        11 L            28 c            45 t            62 +
        12 M            29 d            46 u            63 /
        13 N            30 e            47 v
        14 O            31 f            48 w         (pad) =
        15 P            32 g            49 x
        16 Q            33 h            50 y

   Special processing is performed if fewer than 24 bits are available
   at the end of the data being encoded.  A full encoding quantum is
   always completed at the end of a quantity.  When fewer than 24 input
   bits are available in an input group, bits with value zero are added
   (on the right) to form an integral number of 6-bit groups.  Padding
   at the end of the data is performed using the '=' character.  Since
   all base 64 input is an integral number of octets, only the following
   cases can arise:

   (1) the final quantum of encoding input is an integral multiple of 24
   bits; here, the final unit of encoded output will be an integral
   multiple of 4 characters with no "=" padding,

   (2) the final quantum of encoding input is exactly 8 bits; here, the
   final unit of encoded output will be two characters followed by two
   "=" padding characters, or




Josefsson               Expires November 12, 2006               [Page 7]

Internet-Draft              Base-N encodings                    May 2006


   (3) the final quantum of encoding input is exactly 16 bits; here, the
   final unit of encoded output will be three characters followed by one
   "=" padding character.
















































Josefsson               Expires November 12, 2006               [Page 8]

Internet-Draft              Base-N encodings                    May 2006


5.  Base 64 Encoding With URL And Filename Safe Alphabet

   The Base 64 encoding with an URL and filename safe alphabet has been
   used in [12].

   An alternative alphabet has been suggested that used "~" as the 63rd
   character.  Since the "~" character has special meaning in some file
   system environments, the encoding described in this section is
   recommended instead.  The remaining unreserved URI character is ".",
   but some file system environments does not permit multiple "." in a
   filename, thus making the "." character unattractive as well.

   The pad character "=" is typically percent-encoded when used in an
   URI [9], but if the data length is known implicitly, this can be
   avoided by skipping the padding, see section 3.2.

   This encoding may be referred to as "base64url".  This encoding
   should not be regarded as the same as the "base64" encoding, and
   should not be referred to as only "base64".  Unless made clear,
   "base64" refer to the base 64 in the previous section.

   This encoding is technically identical to the previous one, except
   for the 62:nd and 63:rd alphabet character, as indicated in table 2.

         Table 2: The "URL and Filename safe" Base 64 Alphabet

     Value Encoding  Value Encoding  Value Encoding  Value Encoding
         0 A            17 R            34 i            51 z
         1 B            18 S            35 j            52 0
         2 C            19 T            36 k            53 1
         3 D            20 U            37 l            54 2
         4 E            21 V            38 m            55 3
         5 F            22 W            39 n            56 4
         6 G            23 X            40 o            57 5
         7 H            24 Y            41 p            58 6
         8 I            25 Z            42 q            59 7
         9 J            26 a            43 r            60 8
        10 K            27 b            44 s            61 9
        11 L            28 c            45 t            62 - (minus)
        12 M            29 d            46 u            63 _
        13 N            30 e            47 v           (underline)
        14 O            31 f            48 w
        15 P            32 g            49 x
        16 Q            33 h            50 y         (pad) =







Josefsson               Expires November 12, 2006               [Page 9]

Internet-Draft              Base-N encodings                    May 2006


6.  Base 32 Encoding

   The following description of base 32 is derived from [11] (with
   corrections).  This encoding may be referred to as "base32".

   The Base 32 encoding is designed to represent arbitrary sequences of
   octets in a form that needs to be case insensitive but need not be
   humanly readable.

   A 33-character subset of US-ASCII is used, enabling 5 bits to be
   represented per printable character.  (The extra 33rd character, "=",
   is used to signify a special processing function.)

   The encoding process represents 40-bit groups of input bits as output
   strings of 8 encoded characters.  Proceeding from left to right, a
   40-bit input group is formed by concatenating 5 8bit input groups.
   These 40 bits are then treated as 8 concatenated 5-bit groups, each
   of which is translated into a single character in the base 32
   alphabet.  When encoding a bit stream via the base 32 encoding, the
   bit stream must be presumed to be ordered with the most-significant-
   bit first.  That is, the first bit in the stream will be the high-
   order bit in the first 8bit byte, and the eighth bit will be the low-
   order bit in the first 8bit byte, and so on.

   Each 5-bit group is used as an index into an array of 32 printable
   characters.  The character referenced by the index is placed in the
   output string.  These characters, identified in Table 3, below, are
   selected from US-ASCII digits and uppercase letters.

                     Table 3: The Base 32 Alphabet

     Value Encoding  Value Encoding  Value Encoding  Value Encoding
         0 A             9 J            18 S            27 3
         1 B            10 K            19 T            28 4
         2 C            11 L            20 U            29 5
         3 D            12 M            21 V            30 6
         4 E            13 N            22 W            31 7
         5 F            14 O            23 X
         6 G            15 P            24 Y         (pad) =
         7 H            16 Q            25 Z
         8 I            17 R            26 2

   Special processing is performed if fewer than 40 bits are available
   at the end of the data being encoded.  A full encoding quantum is
   always completed at the end of a body.  When fewer than 40 input bits
   are available in an input group, bits with value zero are added (on
   the right) to form an integral number of 5-bit groups.  Padding at
   the end of the data is performed using the "=" character.  Since all



Josefsson               Expires November 12, 2006              [Page 10]

Internet-Draft              Base-N encodings                    May 2006


   base 32 input is an integral number of octets, only the following
   cases can arise:

   (1) the final quantum of encoding input is an integral multiple of 40
   bits; here, the final unit of encoded output will be an integral
   multiple of 8 characters with no "=" padding,

   (2) the final quantum of encoding input is exactly 8 bits; here, the
   final unit of encoded output will be two characters followed by six
   "=" padding characters,

   (3) the final quantum of encoding input is exactly 16 bits; here, the
   final unit of encoded output will be four characters followed by four
   "=" padding characters,

   (4) the final quantum of encoding input is exactly 24 bits; here, the
   final unit of encoded output will be five characters followed by
   three "=" padding characters, or

   (5) the final quantum of encoding input is exactly 32 bits; here, the
   final unit of encoded output will be seven characters followed by one
   "=" padding character.


7.  Base 32 Encoding With Extended Hex Alphabet

   The following description of base 32 is derived from [7].  This
   encoding may be referred to as "base32hex".  This encoding should not
   be regarded as the same as the "base32" encoding, and should not be
   referred to as only "base32".  This encoding is used by, e.g., NSEC3
   [10]

   One property with this alphabet, that the base64 and base32 alphabet
   lack, is that encoded data maintain its sort order when the encoded
   data is compared bit-wise.

   This encoding is identical to the previous one, except for the
   alphabet.  The new alphabet is found in table 4.













Josefsson               Expires November 12, 2006              [Page 11]

Internet-Draft              Base-N encodings                    May 2006


                 Table 4: The "Extended Hex" Base 32 Alphabet

         Value Encoding  Value Encoding  Value Encoding  Value Encoding
             0 0             9 9            18 I            27 R
             1 1            10 A            19 J            28 S
             2 2            11 B            20 K            29 T
             3 3            12 C            21 L            30 U
             4 4            13 D            22 M            31 V
             5 5            14 E            23 N
             6 6            15 F            24 O         (pad) =
             7 7            16 G            25 P
             8 8            17 H            26 Q







































Josefsson               Expires November 12, 2006              [Page 12]

Internet-Draft              Base-N encodings                    May 2006


8.  Base 16 Encoding

   The following description is original but analogous to previous
   descriptions.  Essentially, Base 16 encoding is the standard case
   insensitive hex encoding, and may be referred to as "base16" or
   "hex".

   A 16-character subset of US-ASCII is used, enabling 4 bits to be
   represented per printable character.

   The encoding process represents 8-bit groups (octets) of input bits
   as output strings of 2 encoded characters.  Proceeding from left to
   right, a 8-bit input is taken from the input data.  These 8 bits are
   then treated as 2 concatenated 4-bit groups, each of which is
   translated into a single character in the base 16 alphabet.

   Each 4-bit group is used as an index into an array of 16 printable
   characters.  The character referenced by the index is placed in the
   output string.

                         Table 5: The Base 16 Alphabet

         Value Encoding  Value Encoding  Value Encoding  Value Encoding
             0 0             4 4             8 8            12 C
             1 1             5 5             9 9            13 D
             2 2             6 6            10 A            14 E
             3 3             7 7            11 B            15 F

   Unlike base 32 and base 64, no special padding is necessary since a
   full code word is always available.





















Josefsson               Expires November 12, 2006              [Page 13]

Internet-Draft              Base-N encodings                    May 2006


9.  Illustrations And Examples

   To translate between binary and a base encoding, the input is stored
   in a structure and the output is extracted.  The case for base 64 is
   displayed in the following figure, borrowed from [5].

            +--first octet--+-second octet--+--third octet--+
            |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
            +-----------+---+-------+-------+---+-----------+
            |5 4 3 2 1 0|5 4 3 2 1 0|5 4 3 2 1 0|5 4 3 2 1 0|
            +--1.index--+--2.index--+--3.index--+--4.index--+

   The case for base 32 is shown in the following figure, borrowed from
   [7].  Each successive character in a base-32 value represents 5
   successive bits of the underlying octet sequence.  Thus, each group
   of 8 characters represents a sequence of 5 octets (40 bits).

                        1          2          3
             01234567 89012345 67890123 45678901 23456789
            +--------+--------+--------+--------+--------+
            |< 1 >< 2| >< 3 ><|.4 >< 5.|>< 6 ><.|7 >< 8 >|
            +--------+--------+--------+--------+--------+
                                                    <===> 8th character
                                              <====> 7th character
                                         <===> 6th character
                                   <====> 5th character
                             <====> 4th character
                        <===> 3rd character
                  <====> 2nd character
             <===> 1st character

   The following example of Base64 data is from [5], with corrections.



















Josefsson               Expires November 12, 2006              [Page 14]

Internet-Draft              Base-N encodings                    May 2006


      Input data:  0x14fb9c03d97e
      Hex:     1   4    f   b    9   c     | 0   3    d   9    7   e
      8-bit:   00010100 11111011 10011100  | 00000011 11011001 01111110
      6-bit:   000101 001111 101110 011100 | 000000 111101 100101 111110
      Decimal: 5      15     46     28       0      61     37     62
      Output:  F      P      u      c        A      9      l      +

      Input data:  0x14fb9c03d9
      Hex:     1   4    f   b    9   c     | 0   3    d   9
      8-bit:   00010100 11111011 10011100  | 00000011 11011001
                                                      pad with 00
      6-bit:   000101 001111 101110 011100 | 000000 111101 100100
      Decimal: 5      15     46     28       0      61     36
                                                         pad with =
      Output:  F      P      u      c        A      9      k      =

      Input data:  0x14fb9c03
      Hex:     1   4    f   b    9   c     | 0   3
      8-bit:   00010100 11111011 10011100  | 00000011
                                             pad with 0000
      6-bit:   000101 001111 101110 011100 | 000000 110000
      Decimal: 5      15     46     28       0      48
                                                  pad with =      =
      Output:  F      P      u      c        A      w      =      =


10.  Test Vectors

   BASE64("") = ""

   BASE64("f") = "Zg=="

   BASE64("fo") = "Zm8="

   BASE64("foo") = "Zm9v"

   BASE64("foob") = "Zm9vYg=="

   BASE64("fooba") = "Zm9vYmE="

   BASE64("foobar") = "Zm9vYmFy"

   BASE32("") = ""

   BASE32("f") = "MY======"

   BASE32("fo") = "MZXQ===="




Josefsson               Expires November 12, 2006              [Page 15]

Internet-Draft              Base-N encodings                    May 2006


   BASE32("foo") = "MZXW6==="

   BASE32("foob") = "MZXW6YQ="

   BASE32("fooba") = "MZXW6YTB"

   BASE32("foobar") = "MZXW6YTBOI======"

   BASE32-HEX("") = ""

   BASE32-HEX("f") = "CO======"

   BASE32-HEX("fo") = "CPNG===="

   BASE32-HEX("foo") = "CPNMU==="

   BASE32-HEX("foob") = "CPNMUOG="

   BASE32-HEX("fooba") = "CPNMUOJ1"

   BASE32-HEX("foobar") = "CPNMUOJ1E8======"

   BASE16("") = ""

   BASE16("f") = "66"

   BASE16("fo") = "666F"

   BASE16("foo") = "666F6F"

   BASE16("foob") = "666F6F62"

   BASE16("fooba") = "666F6F6261"

   BASE16("foobar") = "666F6F626172"


11.  ISO C99 Implementation Of Base64

   Below is an ISO C99 implementation of Base64 encoding and decoding.
   The code assume that the US-ASCII characters are encoding inside
   'char' with values below 255, which holds for all POSIX platforms,
   but should otherwise be portable.  This code is not intended as a
   normative specification of base64.

11.1.  Prototypes: base64.h

   /* base64.h -- Encode binary data using printable characters.



Josefsson               Expires November 12, 2006              [Page 16]

Internet-Draft              Base-N encodings                    May 2006


      Copyright (C) 2004, 2005, 2006 Free Software Foundation, Inc.
      Written by Simon Josefsson.

      This program is free software; you can redistribute it
      and/or modify it under the terms of the GNU Lesser
      General Public License as published by the Free Software
      Foundation; either version 2.1, or (at your option) any
      later version.

      This program is distributed in the hope that it will be
      useful, but WITHOUT ANY WARRANTY; without even the
      implied warranty of MERCHANTABILITY or FITNESS FOR A
      PARTICULAR PURPOSE.  See the GNU Lesser General Public
      License for more details.

      You can retrieve a copy of the GNU Lesser General Public
      License from http://www.gnu.org/licenses/lgpl.txt; or by
      writing to the Free Software Foundation, Inc., 51
      Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */

   #ifndef BASE64_H
   # define BASE64_H

   /* Get size_t. */
   # include <stddef.h>

   /* Get bool. */
   # include <stdbool.h>

   /* This uses that the expression (n+(k-1))/k means the
      smallest integer >= n/k, i.e., the ceiling of n/k.  */
   # define BASE64_LENGTH(inlen) ((((inlen) + 2) / 3) * 4)

   extern bool isbase64 (char ch);

   extern void base64_encode (const char *restrict in,
                              size_t inlen,
                              char *restrict out,
                              size_t outlen);

   extern size_t base64_encode_alloc (const char *in,
                                      size_t inlen,
                                      char **out);

   extern bool base64_decode (const char *restrict in,
                              size_t inlen,
                              char *restrict out,
                              size_t *outlen);



Josefsson               Expires November 12, 2006              [Page 17]

Internet-Draft              Base-N encodings                    May 2006


   extern bool base64_decode_alloc (const char *in,
                                    size_t inlen,
                                    char **out,
                                    size_t *outlen);

   #endif /* BASE64_H */

11.2.  Implementation: base64.c

   /* base64.c -- Encode binary data using printable characters.
      Copyright (C) 1999, 2000, 2001, 2004, 2005, 2006 Free Software
      Foundation, Inc.

      This program is free software; you can redistribute it
      and/or modify it under the terms of the GNU Lesser
      General Public License as published by the Free Software
      Foundation; either version 2.1, or (at your option) any
      later version.

      This program is distributed in the hope that it will be
      useful, but WITHOUT ANY WARRANTY; without even the
      implied warranty of MERCHANTABILITY or FITNESS FOR A
      PARTICULAR PURPOSE.  See the GNU Lesser General Public
      License for more details.

      You can retrieve a copy of the GNU Lesser General Public
      License from http://www.gnu.org/licenses/lgpl.txt; or by
      writing to the Free Software Foundation, Inc., 51
      Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */

   /* Written by Simon Josefsson.  Partially adapted from GNU
    * MailUtils (mailbox/filter_trans.c, as of 2004-11-28).
    * Improved by review from Paul Eggert, Bruno Haible, and
    * Stepan Kasal.
    *
    * Be careful with error checking.  Here is how you would
    * typically use these functions:
    *
    * bool ok = base64_decode_alloc (in, inlen, &out, &outlen);
    * if (!ok)
    *   FAIL: input was not valid base64
    * if (out == NULL)
    *   FAIL: memory allocation error
    * OK: data in OUT/OUTLEN
    *
    * size_t outlen = base64_encode_alloc (in, inlen, &out);
    * if (out == NULL && outlen == 0 && inlen != 0)
    *   FAIL: input too long



Josefsson               Expires November 12, 2006              [Page 18]

Internet-Draft              Base-N encodings                    May 2006


    * if (out == NULL)
    *   FAIL: memory allocation error
    * OK: data in OUT/OUTLEN.
    *
    */

   /* Get prototype. */
   #include "base64.h"

   /* Get malloc. */
   #include <stdlib.h>

   /* Get UCHAR_MAX. */
   #include <limits.h>

   /* C89 compliant way to cast 'char' to 'unsigned char'. */
   static inline unsigned char
   to_uchar (char ch)
   {
     return ch;
   }

   /* Base64 encode IN array of size INLEN into OUT array of
      size OUTLEN.  If OUTLEN is less than
      BASE64_LENGTH(INLEN), write as many bytes as possible.
      If OUTLEN is larger than BASE64_LENGTH(INLEN), also zero
      terminate the output buffer. */
   void
   base64_encode (const char *restrict in, size_t inlen,
                  char *restrict out, size_t outlen)
   {
     static const char b64str[64] =
       "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
       "abcdefghijklmnopqrstuvwxyz0123456789+/";

     while (inlen && outlen)
       {
         *out++ = b64str[to_uchar (in[0]) >> 2];
         if (!--outlen)
           break;
         *out++ = b64str[((to_uchar (in[0]) << 4)
                          + (--inlen ? to_uchar (in[1]) >> 4 : 0))
                         & 0x3f];
         if (!--outlen)
           break;
         *out++ =
           (inlen
            ? b64str[((to_uchar (in[1]) << 2)



Josefsson               Expires November 12, 2006              [Page 19]

Internet-Draft              Base-N encodings                    May 2006


                      + (--inlen ? to_uchar (in[2]) >> 6 : 0))
                     & 0x3f]
            : '=');
         if (!--outlen)
           break;
         *out++ = inlen ? b64str[to_uchar (in[2]) & 0x3f] : '=';
         if (!--outlen)
           break;
         if (inlen)
           inlen--;
         if (inlen)
           in += 3;
       }

     if (outlen)
       *out = '\0';
   }

   /* Allocate a buffer and store zero terminated base64
      encoded data from array IN of size INLEN, returning
      BASE64_LENGTH(INLEN), i.e., the length of the encoded
      data, excluding the terminating zero.  On return, the OUT
      variable will hold a pointer to newly allocated memory
      that must be deallocated by the caller.  If output string
      length would overflow, 0 is returned and OUT is set to
      NULL.  If memory allocation fail, OUT is set to NULL, and
      the return value indicate length of the requested memory
      block, i.e., BASE64_LENGTH(inlen) + 1. */
   size_t
   base64_encode_alloc (const char *in, size_t inlen, char **out)
   {
     size_t outlen = 1 + BASE64_LENGTH (inlen);

     /* Check for overflow in outlen computation.
      *
      * If there is no overflow, outlen >= inlen.
      *
      * If the operation (inlen + 2) overflows then it yields
      * at most +1, so outlen is 0.
      *
      * If the multiplication overflows, we lose at least half
      * of the correct value, so the result is < ((inlen +
      * 2) / 3) * 2, which is less than (inlen + 2) * 0.66667,
      * which is less than inlen as soon as (inlen > 4).
      */
     if (inlen > outlen)
       {
         *out = NULL;



Josefsson               Expires November 12, 2006              [Page 20]

Internet-Draft              Base-N encodings                    May 2006


         return 0;
       }

     *out = malloc (outlen);
     if (*out)
       base64_encode (in, inlen, *out, outlen);

     return outlen - 1;
   }

   /* With this approach this file works independent of the
      charset used (think EBCDIC).  However, it does assume
      that the characters in the Base64 alphabet (A-Za-z0-9+/)
      are encoded in 0..255.  POSIX 1003.1-2001 require that
      char and unsigned char are 8-bit quantities, though,
      taking care of that problem.  But this may be a potential
      problem on non-POSIX C99 platforms.  */
   #define B64(x)                                        \
     ((x) == 'A' ? 0                                \
      : (x) == 'B' ? 1                                \
      : (x) == 'C' ? 2                                \
      : (x) == 'D' ? 3                                \
      : (x) == 'E' ? 4                                \
      : (x) == 'F' ? 5                                \
      : (x) == 'G' ? 6                                \
      : (x) == 'H' ? 7                                \
      : (x) == 'I' ? 8                                \
      : (x) == 'J' ? 9                                \
      : (x) == 'K' ? 10                                \
      : (x) == 'L' ? 11                                \
      : (x) == 'M' ? 12                                \
      : (x) == 'N' ? 13                                \
      : (x) == 'O' ? 14                                \
      : (x) == 'P' ? 15                                \
      : (x) == 'Q' ? 16                                \
      : (x) == 'R' ? 17                                \
      : (x) == 'S' ? 18                                \
      : (x) == 'T' ? 19                                \
      : (x) == 'U' ? 20                                \
      : (x) == 'V' ? 21                                \
      : (x) == 'W' ? 22                                \
      : (x) == 'X' ? 23                                \
      : (x) == 'Y' ? 24                                \
      : (x) == 'Z' ? 25                                \
      : (x) == 'a' ? 26                                \
      : (x) == 'b' ? 27                                \
      : (x) == 'c' ? 28                                \
      : (x) == 'd' ? 29                                \



Josefsson               Expires November 12, 2006              [Page 21]

Internet-Draft              Base-N encodings                    May 2006


      : (x) == 'e' ? 30                                \
      : (x) == 'f' ? 31                                \
      : (x) == 'g' ? 32                                \
      : (x) == 'h' ? 33                                \
      : (x) == 'i' ? 34                                \
      : (x) == 'j' ? 35                                \
      : (x) == 'k' ? 36                                \
      : (x) == 'l' ? 37                                \
      : (x) == 'm' ? 38                                \
      : (x) == 'n' ? 39                                \
      : (x) == 'o' ? 40                                \
      : (x) == 'p' ? 41                                \
      : (x) == 'q' ? 42                                \
      : (x) == 'r' ? 43                                \
      : (x) == 's' ? 44                                \
      : (x) == 't' ? 45                                \
      : (x) == 'u' ? 46                                \
      : (x) == 'v' ? 47                                \
      : (x) == 'w' ? 48                                \
      : (x) == 'x' ? 49                                \
      : (x) == 'y' ? 50                                \
      : (x) == 'z' ? 51                                \
      : (x) == '0' ? 52                                \
      : (x) == '1' ? 53                                \
      : (x) == '2' ? 54                                \
      : (x) == '3' ? 55                                \
      : (x) == '4' ? 56                                \
      : (x) == '5' ? 57                                \
      : (x) == '6' ? 58                                \
      : (x) == '7' ? 59                                \
      : (x) == '8' ? 60                                \
      : (x) == '9' ? 61                                \
      : (x) == '+' ? 62                                \
      : (x) == '/' ? 63                                \
      : -1)

   static const signed char b64[0x100] = {
     B64 (0), B64 (1), B64 (2), B64 (3),
     B64 (4), B64 (5), B64 (6), B64 (7),
     B64 (8), B64 (9), B64 (10), B64 (11),
     B64 (12), B64 (13), B64 (14), B64 (15),
     B64 (16), B64 (17), B64 (18), B64 (19),
     B64 (20), B64 (21), B64 (22), B64 (23),
     B64 (24), B64 (25), B64 (26), B64 (27),
     B64 (28), B64 (29), B64 (30), B64 (31),
     B64 (32), B64 (33), B64 (34), B64 (35),
     B64 (36), B64 (37), B64 (38), B64 (39),
     B64 (40), B64 (41), B64 (42), B64 (43),



Josefsson               Expires November 12, 2006              [Page 22]

Internet-Draft              Base-N encodings                    May 2006


     B64 (44), B64 (45), B64 (46), B64 (47),
     B64 (48), B64 (49), B64 (50), B64 (51),
     B64 (52), B64 (53), B64 (54), B64 (55),
     B64 (56), B64 (57), B64 (58), B64 (59),
     B64 (60), B64 (61), B64 (62), B64 (63),
     B64 (64), B64 (65), B64 (66), B64 (67),
     B64 (68), B64 (69), B64 (70), B64 (71),
     B64 (72), B64 (73), B64 (74), B64 (75),
     B64 (76), B64 (77), B64 (78), B64 (79),
     B64 (80), B64 (81), B64 (82), B64 (83),
     B64 (84), B64 (85), B64 (86), B64 (87),
     B64 (88), B64 (89), B64 (90), B64 (91),
     B64 (92), B64 (93), B64 (94), B64 (95),
     B64 (96), B64 (97), B64 (98), B64 (99),
     B64 (100), B64 (101), B64 (102), B64 (103),
     B64 (104), B64 (105), B64 (106), B64 (107),
     B64 (108), B64 (109), B64 (110), B64 (111),
     B64 (112), B64 (113), B64 (114), B64 (115),
     B64 (116), B64 (117), B64 (118), B64 (119),
     B64 (120), B64 (121), B64 (122), B64 (123),
     B64 (124), B64 (125), B64 (126), B64 (127),
     B64 (128), B64 (129), B64 (130), B64 (131),
     B64 (132), B64 (133), B64 (134), B64 (135),
     B64 (136), B64 (137), B64 (138), B64 (139),
     B64 (140), B64 (141), B64 (142), B64 (143),
     B64 (144), B64 (145), B64 (146), B64 (147),
     B64 (148), B64 (149), B64 (150), B64 (151),
     B64 (152), B64 (153), B64 (154), B64 (155),
     B64 (156), B64 (157), B64 (158), B64 (159),
     B64 (160), B64 (161), B64 (162), B64 (163),
     B64 (164), B64 (165), B64 (166), B64 (167),
     B64 (168), B64 (169), B64 (170), B64 (171),
     B64 (172), B64 (173), B64 (174), B64 (175),
     B64 (176), B64 (177), B64 (178), B64 (179),
     B64 (180), B64 (181), B64 (182), B64 (183),
     B64 (184), B64 (185), B64 (186), B64 (187),
     B64 (188), B64 (189), B64 (190), B64 (191),
     B64 (192), B64 (193), B64 (194), B64 (195),
     B64 (196), B64 (197), B64 (198), B64 (199),
     B64 (200), B64 (201), B64 (202), B64 (203),
     B64 (204), B64 (205), B64 (206), B64 (207),
     B64 (208), B64 (209), B64 (210), B64 (211),
     B64 (212), B64 (213), B64 (214), B64 (215),
     B64 (216), B64 (217), B64 (218), B64 (219),
     B64 (220), B64 (221), B64 (222), B64 (223),
     B64 (224), B64 (225), B64 (226), B64 (227),
     B64 (228), B64 (229), B64 (230), B64 (231),
     B64 (232), B64 (233), B64 (234), B64 (235),



Josefsson               Expires November 12, 2006              [Page 23]

Internet-Draft              Base-N encodings                    May 2006


     B64 (236), B64 (237), B64 (238), B64 (239),
     B64 (240), B64 (241), B64 (242), B64 (243),
     B64 (244), B64 (245), B64 (246), B64 (247),
     B64 (248), B64 (249), B64 (250), B64 (251),
     B64 (252), B64 (253), B64 (254), B64 (255)
   };

   #if UCHAR_MAX == 255
   # define uchar_in_range(c) true
   #else
   # define uchar_in_range(c) ((c) <= 255)
   #endif

   bool
   isbase64 (char ch)
   {
     return uchar_in_range (to_uchar (ch)) && 0 <= b64[to_uchar (ch)];
   }

   /* Decode base64 encoded input array IN of length INLEN to
      output array OUT that can hold *OUTLEN bytes.  Return
      true if decoding was successful, i.e. if the input was
      valid base64 data, false otherwise.  If *OUTLEN is too
      small, as many bytes as possible will be written to OUT.
      On return, *OUTLEN holds the length of decoded bytes in
      OUT.  Note that as soon as any non-alphabet characters
      are encountered, decoding is stopped and false is
      returned.  This means that, when applicable, you must
      remove any line terminators that is part of the data
      stream before calling this function.  */
   bool
   base64_decode (const char *restrict in, size_t inlen,
                  char *restrict out, size_t *outlen)
   {
     size_t outleft = *outlen;

     while (inlen >= 2)
       {
         if (!isbase64 (in[0]) || !isbase64 (in[1]))
           break;

         if (outleft)
           {
             *out++ = ((b64[to_uchar (in[0])] << 2)
                       | (b64[to_uchar (in[1])] >> 4));
             outleft--;
           }




Josefsson               Expires November 12, 2006              [Page 24]

Internet-Draft              Base-N encodings                    May 2006


         if (inlen == 2)
           break;

         if (in[2] == '=')
           {
             if (inlen != 4)
               break;

             if (in[3] != '=')
               break;

           }
         else
           {
             if (!isbase64 (in[2]))
               break;

             if (outleft)
               {
                 *out++ = (((b64[to_uchar (in[1])] << 4) & 0xf0)
                           | (b64[to_uchar (in[2])] >> 2));
                 outleft--;
               }

             if (inlen == 3)
               break;

             if (in[3] == '=')
               {
                 if (inlen != 4)
                   break;
               }
             else
               {
                 if (!isbase64 (in[3]))
                   break;

                 if (outleft)
                   {
                     *out++ = (((b64[to_uchar (in[2])] << 6) & 0xc0)
                               | b64[to_uchar (in[3])]);
                     outleft--;
                   }
               }
           }

         in += 4;
         inlen -= 4;



Josefsson               Expires November 12, 2006              [Page 25]

Internet-Draft              Base-N encodings                    May 2006


       }

     *outlen -= outleft;

     if (inlen != 0)
       return false;

     return true;
   }

   /* Allocate an output buffer in *OUT, and decode the base64
      encoded data stored in IN of size INLEN to the *OUT
      buffer.  On return, the size of the decoded data is
      stored in *OUTLEN.  OUTLEN may be NULL, if the caller is
      not interested in the decoded length.  *OUT may be NULL
      to indicate an out of memory error, in which case *OUTLEN
      contain the size of the memory block needed.  The
      function return true on successful decoding and memory
      allocation errors.  (Use the *OUT and *OUTLEN parameters
      to differentiate between successful decoding and memory
      error.)  The function return false if the input was
      invalid, in which case *OUT is NULL and *OUTLEN is
      undefined. */
   bool
   base64_decode_alloc (const char *in, size_t inlen, char **out,
                        size_t *outlen)
   {
     /* This may allocate a few bytes too much, depending on
        input, but it's not worth the extra CPU time to compute
        the exact amount.  The exact amount is 3 * inlen / 4,
        minus 1 if the input ends with "=" and minus another 1
        if the input ends with "==".  Dividing before
        multiplying avoids the possibility of overflow.  */
     size_t needlen = 3 * (inlen / 4) + 2;

     *out = malloc (needlen);
     if (!*out)
       return true;

     if (!base64_decode (in, inlen, *out, &needlen))
       {
         free (*out);
         *out = NULL;
         return false;
       }

     if (outlen)
       *outlen = needlen;



Josefsson               Expires November 12, 2006              [Page 26]

Internet-Draft              Base-N encodings                    May 2006


     return true;
   }


12.  Security Considerations

   When implementing Base encoding and decoding, care should be taken
   not to introduce vulnerabilities to buffer overflow attacks, or other
   attacks on the implementation.  A decoder should not break on invalid
   input including, e.g., embedded NUL characters (ASCII 0).

   If non-alphabet characters are ignored, instead of causing rejection
   of the entire encoding (as recommended), a covert channel that can be
   used to "leak" information is made possible.  The ignored characters
   could also be used for other nefarious purposes, such as to avoid a
   string equality comparison or to trigger implementation bugs.  The
   implications of ignoring non-alphabet characters should be understood
   in applications that do not follow the recommended practice.
   Similarly, when the base 16 and base 32 alphabets are handled case
   insensitively, alteration of case can be used to leak information or
   make string equality comparisons fail.

   When padding is used, there are some non-significant bits that
   warrant security concerns, they may be abused to leak information,
   used to bypass string equality comparisons, or to trigger
   implementation problems.

   Base encoding visually hides otherwise easily recognized information,
   such as passwords, but does not provide any computational
   confidentiality.  This has been known to cause security incidents
   when, e.g., a user reports details of a network protocol exchange
   (perhaps to illustrate some other problem) and accidentally reveals
   the password because she is unaware that the base encoding does not
   protect the password.

   Base encoding adds no entropy to the plaintext, but it does increase
   the amount of plaintext available and provides a signature for
   cryptanalysis in the form of a characteristic probability
   distribution.


13.  Changes Since RFC 3548

   Added the "base32 extended hex alphabet", needed to preserve sort
   order of encoded data.

   Reference IMAP for the special Base64 encoding used there.




Josefsson               Expires November 12, 2006              [Page 27]

Internet-Draft              Base-N encodings                    May 2006


   Fix the example copied from RFC 2440.

   Add security consideration about providing a signature for
   cryptoanalysis.

   Add test vectors and C99 implementation.

   Typo fixes.


14.  Acknowledgements

   Several people offered comments and/or suggestions, including John E.
   Hadstate, Tony Hansen, Gordon Mohr, John Myers, Chris Newman and
   Andrew Sieber.  Text used in this document are based on earlier RFCs
   describing specific uses of various base encodings.  The author
   acknowledges the RSA Laboratories for supporting the work that led to
   this document.

   This revised version is based in parts on comments and/or suggestions
   made by Roy Arends, Eric Blake, Brian E Carpenter, Elwyn Davies, Bill
   Fenner, Sam Hartman, Ted Hardie, Per Hygum, Jelte Jansen, Clement
   Kent, Tero Kivinen, Paul Kwiatkowski, and Ben Laurie.


15.  Copying Conditions

   Copyright (c) 2000-2006 Simon Josefsson

   Regarding the abstract and section 1, 3, 8, 10, 12, 13, and 14 of
   this document, that were written by Simon Josefsson ("the author",
   for the remainder of this section), the author makes no guarantees
   and is not responsible for any damage resulting from its use.  The
   author grants irrevocable permission to anyone to use, modify, and
   distribute it in any way that does not diminish the rights of anyone
   else to use, modify, and distribute it, provided that redistributed
   derivative works do not contain misleading author or version
   information and do not falsely purport to be IETF RFC documents.
   Derivative works need not be licensed under similar terms.


16.  References

16.1.  Normative References

   [1]  Cerf, V., "ASCII format for network interchange", RFC 20,
        October 1969.




Josefsson               Expires November 12, 2006              [Page 28]

Internet-Draft              Base-N encodings                    May 2006


   [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

16.2.  Informative References

   [3]   Linn, J., "Privacy Enhancement for Internet Electronic Mail:
         Part I: Message Encryption and Authentication Procedures",
         RFC 1421, February 1993.

   [4]   Freed, N. and N. Borenstein, "Multipurpose Internet Mail
         Extensions (MIME) Part One: Format of Internet Message Bodies",
         RFC 2045, November 1996.

   [5]   Callas, J., Donnerhacke, L., Finney, H., and R. Thayer,
         "OpenPGP Message Format", RFC 2440, November 1998.

   [6]   Eastlake, D., "Domain Name System Security Extensions",
         RFC 2535, March 1999.

   [7]   Klyne, G. and L. Masinter, "Identifying Composite Media
         Features", RFC 2938, September 2000.

   [8]   Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
         4rev1", RFC 3501, March 2003.

   [9]   Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
         Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986,
         January 2005.

   [10]  Laurie, B., "DNSSEC Hash Authenticated Denial of Existence",
         draft-ietf-dnsext-nsec3-04 (work in progress), March 2006.

   [11]  Myers, J., "SASL GSSAPI mechanisms", Work in
         progress draft-ietf-cat-sasl-gssapi-01, May 2000.

   [12]  Wilcox-O'Hearn, B., "Post to P2P-hackers mailing list", World
         Wide Web http://zgp.org/pipermail/p2p-hackers/2001-September/
         000315.html, September 2001.













Josefsson               Expires November 12, 2006              [Page 29]

Internet-Draft              Base-N encodings                    May 2006


Author's Address

   Simon Josefsson
   SJD

   Email: simon@josefsson.org













































Josefsson               Expires November 12, 2006              [Page 30]

Internet-Draft              Base-N encodings                    May 2006


Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.


Disclaimer of Validity

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Copyright Statement

   Copyright (C) The Internet Society (2006).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.


Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.




Josefsson               Expires November 12, 2006              [Page 31]


Html markup produced by rfcmarkup 1.107, available from http://tools.ietf.org/tools/rfcmarkup/