RC4

RC4 (also called ARC4 or ARCFour) is a cryptographic stream cipher, designed by Ron Rivest in 1987. It was originally a trade secret that was licensed for use in proprietary software. It was leaked or reverse-engineered in 1994.

RC4 is unusual in that it is purely a stream cipher, not a CBC (cipher block chaining) mode of a block cipher.

Though not completely broken (as far as we know), several cryptographic weaknesses have been found in it. Its use is discouraged.

Software

 * OpenSSL
 * MCrypt

Links

 * Wikipedia article
 * RC4 Tutorial with Animation
 * Cryptography - RC4 Algorithm
 * Attack of the week: RC4 is kind of broken in TLS
 * Have spooks smashed RC4?
 * RFC 7465: Prohibiting RC4 Cipher Suites