RC2
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182186371
2008-01-04T22:05:11Z
Admc2006
2310158
moved [[RC2 (cipher)]] to [[RC2]] over redirect: revert
{{Infobox block cipher
| name = RC2
| image = [[Image:RC2 InfoBox Diagram.png|280px|center]]
| 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 2<sup>34</sup> [[chosen plaintext]]s (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 (cipher)|RC4]], [[RC5]] and [[RC6]].
The development of RC2 was sponsored by [[Lotus Software|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 encryption|40-bit]] [[key size]] was treated favourably under US [[Export of cryptography|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 engineering|reverse engineered]].
RC2 is a [[block size (cryptography)|64-bit block]] cipher with a variable size [[key (cryptography)|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 2<sup>34</sup> [[chosen plaintext]]s (Kelsey et al, 1997).
==Sources==
* [[Steven Levy]], [[Crypto: How the Code Rebels Beat the Government Saving Privacy in the Digital Age|Crypto: How the Code Rebels Beat the Government — Saving Privacy in the Digital Age]], ISBN 0-14-024432-8, 2001.
==References==
* [[Lars Knudsen|Lars R. Knudsen]], [[Vincent Rijmen]], Ronald L. Rivest, [[Matt Robshaw|Matthew J. B. Robshaw]]: On the Design and Security of RC2. [[Fast Software Encryption]] 1998: 206–221
* [[John Kelsey (cryptanalyst)|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]
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