RFC 3492 (rfc3492) - Page 1 of 35


Punycode: A Bootstring encoding of Unicode for Internationalized Domain Names in Applications (IDNA)



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Network Working Group                                        A. Costello
Request for Comments: 3492                 Univ. of California, Berkeley
Category: Standards Track                                     March 2003


              Punycode: A Bootstring encoding of Unicode
       for Internationalized Domain Names in Applications (IDNA)

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   Punycode is a simple and efficient transfer encoding syntax designed
   for use with Internationalized Domain Names in Applications (IDNA).
   It uniquely and reversibly transforms a Unicode string into an ASCII
   string.  ASCII characters in the Unicode string are represented
   literally, and non-ASCII characters are represented by ASCII
   characters that are allowed in host name labels (letters, digits, and
   hyphens).  This document defines a general algorithm called
   Bootstring that allows a string of basic code points to uniquely
   represent any string of code points drawn from a larger set.
   Punycode is an instance of Bootstring that uses particular parameter
   values specified by this document, appropriate for IDNA.

Table of Contents

   1. Introduction...............................................2
       1.1 Features..............................................2
       1.2 Interaction of protocol parts.........................3
   2. Terminology................................................3
   3. Bootstring description.....................................4
       3.1 Basic code point segregation..........................4
       3.2 Insertion unsort coding...............................4
       3.3 Generalized variable-length integers..................5
       3.4 Bias adaptation.......................................7
   4. Bootstring parameters......................................8
   5. Parameter values for Punycode..............................8
   6. Bootstring algorithms......................................9



Costello                    Standards Track


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