WEP uses a 24-bit initialization vector that is different for each frame.

• A. True
• B. False
• C. Not applicable
• D. Not sure

Answer: (A)

WEP uses the RC4 stream cipher seeded with a 24-bit initialization vector that is included with each frame to produce a different keystream for that frame. The IV is sent in the clear, and the receiver combines it with the secret WEP key to initialize RC4, so each frame gets its own keystream and its ciphertext is produced by XORing plaintext with that keystream. The 24-bit IV provides 16,777,216 possible values, which is the mechanism intended to yield a different keystream for every frame. In practice, because the IV space is finite, IVs can repeat over a long stream of frames, which is what creates the security vulnerabilities behind WEP. But the design goal described by the statement is correct: the IV is 24-bit and intended to be different for each frame.