Editing RC4 (section)

{{short description|Stream cipher}}
{{About|the stream cipher}}
{{Use dmy dates|date=December 2015}}
{{Infobox encryption method
|name           = RC4
|image          =
|caption        =
|designers      = [[Ron Rivest]] ([[RSA Security]])
|publish date   = Leaked in 1994<br/>(designed in 1987)
|series         =
|derived from   =
|related to     =
|certification  =
|key size       = 40–{{val|2048}} bits
|security claim =
|state size     = {{val|2064}} bits ({{val|1684}} effective)
|structure      =
|rounds         = 1
|speed          = 7 cycles per byte on [[Intel P5 (microarchitecture)|original Pentium]]<ref>{{cite conference |author1=P. Prasithsangaree |author2=P. Krishnamurthy |conference=GLOBECOM '03 |publisher=IEEE |year=2003 |title=Analysis of Energy Consumption of RC4 and AES Algorithms in Wireless LANs |url=http://www.sis.pitt.edu/~is3966/group5_paper2.pdf |archive-url=https://web.archive.org/web/20131203082918/http://www.sis.pitt.edu/~is3966/group5_paper2.pdf |archive-date=3 December 2013 |url-status=dead }}</ref><br>Modified Alleged RC4 on Intel Core 2: 13.9 cycles per byte<ref>{{cite web |title=Crypto++ 5.6.0 Benchmarks |url=http://www.cryptopp.com/benchmarks.html |access-date=22 September 2015}}</ref>
|cryptanalysis  =
}}

In [[cryptography]], '''RC4''' (Rivest Cipher 4, also known as '''ARC4''' or '''ARCFOUR''', meaning Alleged RC4, see below) is a [[stream cipher]]. While it is remarkable for its simplicity and speed in software, multiple vulnerabilities have been discovered in RC4, rendering it insecure.<ref name=rfc7465>{{cite IETF |rfc=7465 |author=Andrei Popov |date=February 2015 |title=Prohibiting RC4 Cipher Suites }}</ref><ref>{{cite news |url=http://www.computerworld.com/article/2489395/encryption/microsoft-continues-rc4-encryption-phase-out-plan-with--net-security-updates.html |author=Lucian Constantin |date=14 May 2014 |title=Microsoft continues RC4 encryption phase-out plan with .NET security updates |work=ComputerWorld }}</ref> It is especially vulnerable when the beginning of the output [[keystream]] is not discarded, or when nonrandom or related keys are used. Particularly problematic uses of RC4 have led to very insecure [[Cryptographic protocol|protocol]]s such as [[Wired Equivalent Privacy|WEP]].<ref>{{citation |page=77 |year=2014 |author1=J. Katz |author2=Y. Lindell |title=Introduction to Modern Cryptography |publisher=Chapman and Hall/CRC}}.</ref>

{{As of|2015}}, there is speculation that some state cryptologic agencies may possess the capability to break RC4 when used in the [[Transport Layer Security|TLS protocol]].<ref name=Leyden20130906/> [[IETF]] has published RFC 7465 to prohibit the use of RC4 in TLS;<ref name=rfc7465 /> [[Mozilla]] and [[Microsoft]] have issued similar recommendations.<ref>{{cite web|url=https://wiki.mozilla.org/Security/Server_Side_TLS|title=Mozilla Security Server Side TLS Recommended Configurations|publisher=Mozilla|access-date=2015-01-03}}</ref><ref>{{cite web|url=http://blogs.technet.com/b/srd/archive/2013/11/12/security-advisory-2868725-recommendation-to-disable-rc4.aspx|title=Security Advisory 2868725: Recommendation to disable RC4|date=12 November 2013|publisher=Microsoft|access-date=2013-12-04}}</ref>

A number of attempts have been made to strengthen RC4, notably Spritz, RC4A, [[Variably Modified Permutation Composition|VMPC]], and RC4<sup>+</sup>.