View source for RC2

{{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"<ref>{{cite web| url = http://people.csail.mit.edu/rivest/faq.html#Ron| title = Rivest FAQ at csail.mit.edu}}</ref> (see also [[RC2]], [[RC5]] and [[RC6]]), but generally called simply RC2. Other ciphers designed by Ron 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}}

==References==
{{Reflist}}

==Bibliography==
{{refbegin}}
* {{cite book |last1=Kelsey |first1=John |author-link1=John Kelsey (cryptanalyst) |last2=Schneier |first2=Bruce |author-link2=Bruce Schneier |last3=Wagner |first3=David |title=Information and Communications Security |chapter=Related-key cryptanalysis of 3-WAY, Biham-DES, CAST, DES-X, NewDES, RC2, and TEA |series=Lecture Notes in Computer Science |author-link3=David A. Wagner |editor1-last=Han |editor1-first=Y. |editor2-last=Okamoto |editor2-first=T. |editor3-last=Qing |editor3-first=S. |date=1997 |volume=1334 |pages=233–246 |doi=10.1007/BFb0028479 |chapter-url=https://www.schneier.com/academic/archives/1997/11/related-key_cryptana.html |access-date=2018-10-10 |publisher=Springer, Berlin, Heidelberg|isbn=978-3-540-63696-0 }}
* {{cite book |last1=Knudsen |first1=Lars R. |last2=Rijmen |first2=Vincent |last3=Rivest |first3=Ronald L. |last4=Robshaw |first4=Matthew J. B. |title=Fast Software Encryption |chapter=On the Design and Security of RC2 |author-link1=Lars Knudsen |author-link2=Vincent Rijmen |author-link4=Matt Robshaw |series=Lecture Notes in Computer Science |date=1998-08-16 |volume=1372 |pages=206–221 |doi=10.1007/3-540-69710-1_14 |chapter-url=https://people.csail.mit.edu/rivest/pubs/KRRR98.pdf |access-date=2018-10-10 |publisher=Springer Berlin Heidelberg |isbn=978-3-540-64265-7 |language=en|doi-access=free }}
* {{cite book |last1=Levy |first1=Steven |author-link1=Steven Levy |title=[[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]] |date=2001 |publisher=Penguin Books |isbn=0-14-024432-8}}
{{refend}}

==External links==
* {{IETF RFC|2268|link=no}} - A Description of the RC2(r) Encryption Algorithm
* [http://security.nknu.edu.tw/crypto/faq/html/3-6-2.html RSA FAQ: What is RC2?] {{Webarchive|url=https://web.archive.org/web/20160303204419/http://security.nknu.edu.tw/crypto/faq/html/3-6-2.html |date=2016-03-03 }}
* [https://groups.google.com/g/sci.crypt/c/m1UFiFMC89Y/m/cLyO5tr1g_MJ sci.crypt posting revealing the RC2 algorithm]

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[[Category:Broken block ciphers]]