What is RC4?

RC4, also known as Rivest Cipher 4, is a symmetric key stream cipher designed by Ron Rivest in 1987.  The National Institute of Standards and Technology (NIST) has discouraged the use of RC4 in favor of more secure cryptographic algorithms. NIST has published guidelines and recommendations for cryptographic algorithms, and RC4 is generally considered insecure for applications requiring strong security. 

RC4 is one of the most commonly used stream ciphers, having been used in Secure Socket Layer (SSL)/ Transport Layer Security (TLS) protocols, IEEE 802.11 wireless LAN standard, and the Wi-Fi Security Protocol WEP (Wireless Equivalent Protocol). RC4 owes its popularity, relating to stream ciphers, to its ease of use and performance speed. Now, significant flaws mean RC4 is not used nearly as often as before.