RC2

Infobox block cipher
name = RC2


caption = The MIX transformation of RC2; four of these comprise a MIXING round
designers = Ron Rivest
publish date = leaked in 1996, designed in 1987
derived from =
derived to =
key size = 8–128 bits, in steps of 8 bits; default 64 bits
block size = 64 bits
structure = Source-heavy Feistel network
rounds = 16 of type MIXING, 2 of type MASHING
cryptanalysis = A related-key attack is possible requiring 2³⁴ chosen plaintexts (Kelsey et al, 1997).

In cryptography, RC2 is a block cipher designed by Ron Rivest in 1987. "RC" stands for "Ron's Code" or "Rivest Cipher"; other ciphers designed by Rivest include RC4, RC5 and RC6.

The development of RC2 was sponsored by Lotus, who were seeking a custom cipher that, after evaluation by the NSA, could be exported as part of their Lotus Notes software. The NSA suggested a couple of changes, which Rivest incorporated. After further negotiations, the cipher was approved for export in 1989. Along with RC4, RC2 with a 40-bit key size was treated favourably under US export regulations for cryptography.

Initially, the details of the algorithm were kept secret — proprietary to RSA Security — but on 29th January, 1996, source code for RC2 was anonymously posted to the Internet on the Usenet forum, sci.crypt. A similar disclosure had occurred earlier with RC4. It is unclear whether the poster had access to the specifications or whether it had been reverse engineered.

RC2 is a 64-bit block cipher with a variable size key. Its 18 rounds are arranged as a source-heavy Feistel network, with 16 rounds of one type ("MIXING") punctuated by two rounds of another type ("MASHING"). A MIXING round consists of four applications of the MIX transformation, as shown in the diagram.

RC2 is vulnerable to a related-key attack using 2³⁴ chosen plaintexts (Kelsey et al, 1997).

ources

* Steven Levy, , ISBN 0-14-024432-8, 2001.

References

* Lars R. Knudsen, Vincent Rijmen, Ronald L. Rivest, Matthew J. B. Robshaw: On the Design and Security of RC2. Fast Software Encryption 1998: 206–221
* John Kelsey, Bruce Schneier, David Wagner: Related-key cryptanalysis of 3-WAY, Biham-DES, CAST, DES-X, NewDES, RC2, and TEA. ICICS 1997: 233–246

External links

* RFC 2268 - A Description of the RC2(r) Encryption Algorithm
* [http://www.rsasecurity.com/rsalabs/node.asp?id=2249 RSA FAQ: What is RC2?]
* [http://groups.google.com/groups?selm=4ehmfs%246nq%40utopia.hacktic.nl sci.crypt posting revealing the RC2 algorithm]