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Security Fundamentals & Crypto · Intermediate

Rivest Cipher 4 (RC4)

Legacy stream cipher once used in WEP, WPA-TKIP, and SSL/TLS, now prohibited due to biases.

Definition

RC4 is a simple, fast stream cipher designed by Ron Rivest in 1987. Statistical biases in its keystream enable plaintext recovery, and RFC 7465 prohibits its use in TLS. It should not be used in any modern system.

Example

WEP's use of RC4 with short IVs allowed attackers to crack keys in minutes.

Exam tip

RC4 is the stream cipher behind WEP and TKIP; any answer recommending RC4 is wrong.

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