rfc2268.txt

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   R[i] = R[i] ror s[i];
   R[i] = R[i] - K[j] - (R[i-1] & R[i-2]) - ((~R[i-1]) & R[i-3]);
   j = j - 1;

   In words: R[i] is rotated right by s[i] bits (bits rotated out the
   right end of R[i] are brought back in at the left). Here j is a
   "global" variable so that K[j] is always the key word with greatest
   index in the expanded key which has not yet been used in a "r-mix"
   operation. The key word K[j] is subtracted from R[i], and j is
   decremented. R[i-1] is used to create a "composite" word which is
   subtracted from R[i].  The composite word is identical with R[i-2] in
   those positions where R[i-1] is one, and identical to R[i-3] in those
   positions where R[i-1] is zero.

4.2 R-Mixing round

   An "r-mixing round" consists of the following operations:

   R-Mix up R[3]
   R-Mix up R[2]
   R-Mix up R[1]
   R-Mix up R[0]





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RFC 2268              RC2(r) Encryption Algorithm             March 1998


4.3 R-Mash R[i]

   The primitive "R-Mash R[i]" operation is defined as follows (using
   the previous conventions regarding subscripts for R):

   R[i] = R[i] - K[R[i-1] & 63];

   In words: R[i] is "r-mashed" by subtracting from it one of the words
   of the expanded key. The key word to be used is determined by looking
   at the low-order six bits of R[i-1], and using that as an index into
   the key array K.

4.4 R-Mashing round

   An "r-mashing round" consists of:

   R-Mash R[3]
   R-Mash R[2]
   R-Mash R[1]
   R-Mash R[0]

4.5 Decryption operation

   The entire decryption operation can now be described as follows.
   Here j is a global integer variable which is affected by the mixing
   operations.

        1. Initialize words R[0], ..., R[3] to contain the 64-bit
           ciphertext value.

        2. Expand the key, so that words K[0], ..., K[63] become
           defined.

        3. Initialize j to 63.

        4. Perform five r-mixing rounds.

        5. Perform one r-mashing round.

        6. Perform six r-mixing rounds.

        7. Perform one r-mashing round.

        8. Perform five r-mixing rounds.

5. Test vectors

   Test vectors for encryption with RC2 are provided below.



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   All quantities are given in hexadecimal notation.

   Key length (bytes) = 8
   Effective key length (bits) = 63
   Key = 00000000 00000000
   Plaintext = 00000000 00000000
   Ciphertext = ebb773f9 93278eff

   Key length (bytes) = 8
   Effective key length (bits) = 64
   Key = ffffffff ffffffff
   Plaintext = ffffffff ffffffff
   Ciphertext = 278b27e4 2e2f0d49

   Key length (bytes) = 8
   Effective key length (bits) = 64
   Key = 30000000 00000000
   Plaintext = 10000000 00000001
   Ciphertext = 30649edf 9be7d2c2

   Key length (bytes) = 1
   Effective key length (bits) = 64
   Key = 88
   Plaintext = 00000000 00000000
   Ciphertext = 61a8a244 adacccf0

   Key length (bytes) = 7
   Effective key length (bits) = 64
   Key = 88bca90e 90875a
   Plaintext = 00000000 00000000
   Ciphertext = 6ccf4308 974c267f

   Key length (bytes) = 16
   Effective key length (bits) = 64
   Key = 88bca90e 90875a7f 0f79c384 627bafb2
   Plaintext = 00000000 00000000
   Ciphertext = 1a807d27 2bbe5db1

   Key length (bytes) = 16
   Effective key length (bits) = 128
   Key = 88bca90e 90875a7f 0f79c384 627bafb2
   Plaintext = 00000000 00000000
   Ciphertext = 2269552a b0f85ca6

   Key length (bytes) = 33
   Effective key length (bits) = 129
   Key = 88bca90e 90875a7f 0f79c384 627bafb2 16f80a6f 85920584
         c42fceb0 be255daf 1e



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   Plaintext = 00000000 00000000
   Ciphertext = 5b78d3a4 3dfff1f1

6. RC2 Algorithm Object Identifier

   The Object Identifier for RC2 in cipher block chaining mode is

   rc2CBC OBJECT IDENTIFIER
     ::= {iso(1) member-body(2) US(840) rsadsi(113549)
          encryptionAlgorithm(3) 2}

   RC2-CBC takes parameters

   RC2-CBCParameter ::= CHOICE {
     iv IV,
     params SEQUENCE {
       version RC2Version,
       iv IV
     }
   }

   where

   IV ::= OCTET STRING -- 8 octets
   RC2Version ::= INTEGER -- 1-1024

   RC2 in CBC mode has two parameters: an 8-byte initialization vector
   (IV) and a version number in the range 1-1024 which specifies in a
   roundabout manner the number of effective key bits to be used for the
   RC2 encryption/decryption.

   The correspondence between effective key bits and version number is
   as follows:

   1. If the number EKB of effective key bits is in the range 1-255,
      then the version number is given by Table[EKB], where the 256-byte
      translation table Table[] is specified below. Table[] specifies a
      permutation on the numbers 0-255; note that it is not the same
      table that appears in the key expansion phase of RC2.

   2. If the number EKB of effective key bits is in the range
      256-1024, then the version number is simply EKB.

      The default number of effective key bits for RC2 is 32. If RC2-CBC
      is being performed with 32 effective key bits, the parameters
      should be supplied as a simple IV, rather than as a SEQUENCE
      containing a version and an IV.




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RFC 2268              RC2(r) Encryption Algorithm             March 1998


        0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f

   00: bd 56 ea f2 a2 f1 ac 2a b0 93 d1 9c 1b 33 fd d0
   10: 30 04 b6 dc 7d df 32 4b f7 cb 45 9b 31 bb 21 5a
   20: 41 9f e1 d9 4a 4d 9e da a0 68 2c c3 27 5f 80 36
   30: 3e ee fb 95 1a fe ce a8 34 a9 13 f0 a6 3f d8 0c
   40: 78 24 af 23 52 c1 67 17 f5 66 90 e7 e8 07 b8 60
   50: 48 e6 1e 53 f3 92 a4 72 8c 08 15 6e 86 00 84 fa
   60: f4 7f 8a 42 19 f6 db cd 14 8d 50 12 ba 3c 06 4e
   70: ec b3 35 11 a1 88 8e 2b 94 99 b7 71 74 d3 e4 bf
   80: 3a de 96 0e bc 0a ed 77 fc 37 6b 03 79 89 62 c6
   90: d7 c0 d2 7c 6a 8b 22 a3 5b 05 5d 02 75 d5 61 e3
   a0: 18 8f 55 51 ad 1f 0b 5e 85 e5 c2 57 63 ca 3d 6c
   b0: b4 c5 cc 70 b2 91 59 0d 47 20 c8 4f 58 e0 01 e2
   c0: 16 38 c4 6f 3b 0f 65 46 be 7e 2d 7b 82 f9 40 b5
   d0: 1d 73 f8 eb 26 c7 87 97 25 54 b1 28 aa 98 9d a5
   e0: 64 6d 7a d4 10 81 44 ef 49 d6 ae 2e dd 76 5c 2f
   f0: a7 1c c9 09 69 9a 83 cf 29 39 b9 e9 4c ff 43 ab

A. Intellectual Property Notice

   RC2 is a registered trademark of RSA Data Security, Inc. RSA's
   copyrighted RC2 software is available under license from RSA Data
   Security, Inc.

B. Author's Address

   Ron Rivest
   RSA Laboratories
   100 Marine Parkway, #500
   Redwood City, CA  94065  USA

   Phone: [phone]
   EMail: [e-mail]

















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C.  Full Copyright Statement

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

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS 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.
























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