Editing RC4 (section)

===RC4-based random number generators===
Several [[operating system]]s include {{code|arc4random}}, an API originating in [[OpenBSD security features|OpenBSD]] providing access to a random number generator originally based on RC4. The API allows no seeding, as the function initializes itself using [[/dev/random]]. The use of RC4 has been phased out in most systems implementing this API. [[Man page]]s for the new arc4random include the [[backronym]] "A Replacement Call for Random" for ARC4 as a mnemonic, as it provides better random data than [[rand()]] does.<ref name=arc4random-obsd>{{cite web |url=http://man.openbsd.org/arc4random.3 |title=arc4random(3) |publisher=OpenBSD}}</ref>

* In OpenBSD 5.5, released in May 2014, {{code|arc4random}} was modified to use [[ChaCha20]].<ref>{{cite web |title=OpenBSD 5.5 |url=http://www.openbsd.org/55.html |access-date=21 September 2014}}</ref><ref>{{cite web |url=http://bxr.su/OpenBSD/lib/libc/crypt/arc4random.c |title=libc/crypt/arc4random.c |website=BSD Cross Reference, OpenBSD src/lib/ |editor=deraadt |editor-link=Theo de Raadt |date=21 July 2014 |access-date=2015-01-13 |quote=ChaCha based random number generator for OpenBSD.}}</ref> The implementations of arc4random in [[FreeBSD]], [[NetBSD]]<ref>{{cite web |url=http://bxr.su/NetBSD/lib/libc/gen/arc4random.c |title=libc/gen/arc4random.c |website=BSD Cross Reference, NetBSD src/lib/ |editor=riastradh |date=16 November 2014 |access-date=2015-01-13 |quote=Legacy arc4random(3) API from OpenBSD reimplemented using the ChaCha20 PRF, with per-thread state.}}</ref><ref>{{cite web |title=arc4random – NetBSD Manual Pages |url=http://netbsd.gw.com/cgi-bin/man-cgi?arc4random++NetBSD-current |access-date=6 January 2015 |archive-date=6 July 2020 |archive-url=https://web.archive.org/web/20200706210612/https://netbsd.gw.com/cgi-bin/man-cgi?arc4random++NetBSD-current |url-status=dead}}</ref> also use ChaCha20.
** Linux typically uses [[glibc]], which did not offer ''arc4random'' until 2022. Instead, a separate library, libbsd, offers the function; it was updated to use ChaCha20 in 2016.<ref>{{cite web |title=Update arc4random module from OpenBSD and LibreSSL |url=https://cgit.freedesktop.org/libbsd/commit/?id=874a0e5 |access-date=6 January 2016}}</ref> In 2022, [[glibc]] added its own version of ''arc4random'', also based on ChaCha20.<ref>{{cite web |title=GNU C Library Finally Adds arc4random Functions For Linux |url=https://www.phoronix.com/news/GNU-Glibc-arc4random-Functions |website=www.phoronix.com |language=en}}</ref>
* According to manual pages shipped with the operating system, in the 2017 release of [[macOS]] and [[iOS]] operating systems, Apple replaced RC4 with AES in its implementation of arc4random. 

Proposed new random number generators are often compared to the RC4 random number generator.<ref>
Bartosz Zoltak.
[//eprint.iacr.org/2013/768.pdf "VMPC-R: Cryptographically Secure Pseudo-Random Number Generator, Alternative to RC4"].
2010?
</ref><ref>
Chefranov, A. G.
[https://ieeexplore.ieee.org/document/4022919/ "Pseudo-Random Number Generator RC4 Period Improvement"].
2006.
</ref>

Several attacks on RC4 are able to [[ciphertext indistinguishability#Indistinguishable from random noise|distinguish its output from a random sequence]].<ref name="mantin" />