RFC 2268 (rfc2268) - Page 1 of 11

A Description of the RC2(r) Encryption Algorithm

Network Working Group                                          R. Rivest
Request for Comments: 2268           MIT Laboratory for Computer Science
Category: Informational                      and RSA Data Security, Inc.
                                                              March 1998


            A Description of the RC2(r) Encryption Algorithm

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

1. Introduction

   This memo is an RSA Laboratories Technical Note.  It is meant for
   informational use by the Internet community.

   This memo describes a conventional (secret-key) block encryption
   algorithm, called RC2, which may be considered as a proposal for a
   DES replacement. The input and output block sizes are 64 bits each.
   The key size is variable, from one byte up to 128 bytes, although the
   current implementation uses eight bytes.

   The algorithm is designed to be easy to implement on 16-bit
   microprocessors. On an IBM AT, the encryption runs about twice as
   fast as DES (assuming that key expansion has been done).

1.1 Algorithm description

   We use the term "word" to denote a 16-bit quantity. The symbol + will
   denote twos-complement addition. The symbol & will denote the bitwise
   "and" operation. The term XOR will denote the bitwise "exclusive-or"
   operation. The symbol ~ will denote bitwise complement.  The symbol ^
   will denote the exponentiation operation.  The term MOD will denote
   the modulo operation.

   There are three separate algorithms involved:

     Key expansion. This takes a (variable-length) input key and
     produces an expanded key consisting of 64 words K[0],...,K[63].





Rivest                       Informational