WEP encrypts each frame with a per-frame key that consists of the shared RC4 key plus a 24-bit initialization vector that is different for each frame.

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

Answer: (D)

The key idea here is how WEP creates a per-frame encryption key. In WEP, each frame is encrypted using RC4 with a key that combines the shared WEP key (the secret key) with a per-frame 24-bit initialization vector. That IV is included in the frame header in cleartext, and for every new frame a different 24-bit IV is used so the RC4 keystream changes each time. Practically, the per-frame RC4 key is the IV concatenated with the shared WEP key, so you get a unique keystream for each frame. That’s why the statement is true: the per-frame key consists of the shared RC4 key plus a distinct 24-bit IV for each frame.