Editing RC2 (section)

{{Short description|Block cipher}}
{{other uses}}
{{Infobox block cipher
| name          = RC2
| image         = RC2 InfoBox Diagram.svg
| image_size    = 280px
| caption       = The MIX transformation of RC2; four of these comprise a MIXING round
| designers     = [[Ron Rivest]]
| publish date  = Leaked in 1996, designed in 1987, officially published in 1998
| derived from  = 
| derived to    = 
| key size      = 1&ndash;128 bytes
| block size    = 64 bits
| structure     = Source-heavy unbalanced [[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''' (also known as '''ARC2''') is a [[Symmetric-key algorithm|symmetric-key]] [[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 few 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 &mdash; proprietary to [[RSA Security]] &mdash; but on 29 January 1996, source code for RC2 was anonymously posted to the Internet on the [[Usenet]] forum [[sci.crypt]]. Mentions of [[CodeView]] and [[SoftICE]] (popular [[debugger]]s) suggest that it had been [[reverse engineering|reverse engineered]]. A similar disclosure had occurred earlier with RC4.

In March 1998, Ron Rivest authored an [[Request for Comments|RFC]] publicly describing RC2 himself.<ref>{{cite IETF|rfc=2268}}</ref>

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 unbalanced [[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.{{sfn|Kelsey|Schneier|Wagner|1997}}