What initialization vector (IV) length do most weak WEP implementations use?

What initialization vector (IV) length do most weak WEP implementations use?

• A. 16 bit
• B. 24 bit
• C. 32 bit
• D. 64 bit

Answer: (B)

The key idea is how the IV seeds the RC4 keystream in WEP. In weak WEP, the initialization vector is only twenty-four bits long, which gives 16,777,216 possible IV values. In a busy wireless network, those IVs can start looping back to the same values quickly, causing the same keystream to be reused with different plaintext. When the same keystream is used more than once, an attacker can compare the resulting ciphertexts to reveal information about the plaintext and the key, making the cipher far easier to crack. That small IV space is what makes WEP so vulnerable in practice, so the twenty-four-bit IV is the defining characteristic of those weak implementations.

The key idea is how the IV seeds the RC4 keystream in WEP. In weak WEP, the initialization vector is only twenty-four bits long, which gives 16,777,216 possible IV values. In a busy wireless network, those IVs can start looping back to the same values quickly, causing the same keystream to be reused with different plaintext. When the same keystream is used more than once, an attacker can compare the resulting ciphertexts to reveal information about the plaintext and the key, making the cipher far easier to crack. That small IV space is what makes WEP so vulnerable in practice, so the twenty-four-bit IV is the defining characteristic of those weak implementations.