What is the main security weakness of WEP that makes it susceptible to rapid key cracking?

What is the main security weakness of WEP that makes it susceptible to rapid key cracking?

• A. No encryption
• B. Strong encryption
• C. Frequent key rotation
• D. Weak IVs

Answer: (D)

The vulnerability being tested is the weak initialization vector (IV) used by WEP. WEP relies on RC4, a stream cipher, where each packet is encrypted with a keystream generated from a secret key plus a per-packet 24-bit IV. Since the IV space is only 2^24 values, IVs repeat very quickly as traffic flows. When two or more packets are encrypted with the same IV, the same portion of the keystream is used, so XORing those ciphertexts cancels that keystream portion and yields the XOR of the two plaintexts. With enough captured traffic, an attacker can exploit these repeated keystreams (and the known biases in RC4’s early keystream bytes) to recover the keystream or even the WEP key itself, allowing rapid decryption of traffic. In short, the small, reused IVs make the keystream predictable and crackable, which is why weak IVs are the core weakness here.

The vulnerability being tested is the weak initialization vector (IV) used by WEP. WEP relies on RC4, a stream cipher, where each packet is encrypted with a keystream generated from a secret key plus a per-packet 24-bit IV. Since the IV space is only 2^24 values, IVs repeat very quickly as traffic flows. When two or more packets are encrypted with the same IV, the same portion of the keystream is used, so XORing those ciphertexts cancels that keystream portion and yields the XOR of the two plaintexts. With enough captured traffic, an attacker can exploit these repeated keystreams (and the known biases in RC4’s early keystream bytes) to recover the keystream or even the WEP key itself, allowing rapid decryption of traffic. In short, the small, reused IVs make the keystream predictable and crackable, which is why weak IVs are the core weakness here.