A practical attack on WEP involves observing two frames that used the same key.

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Multiple Choice

A practical attack on WEP involves observing two frames that used the same key.

Explanation:
WEP encrypts each frame with RC4 using a seed formed from the shared key and a per-frame IV. Because the IV space is only 24 bits, the same seed (and thus the same keystream) repeats across frames fairly often in practice. When two frames are encrypted with the same keystream, XORing their ciphertexts cancels the keystream and leaves the XOR of the two plaintexts. With knowledge of some plaintext or by exploiting RC4 biases, an attacker can turn this into recovering plaintexts or the keystream itself, enabling further decryption of other frames. This reuse of the keystream from frames that effectively used the same key is the core weakness WEP attacks exploit, making the statement true.

WEP encrypts each frame with RC4 using a seed formed from the shared key and a per-frame IV. Because the IV space is only 24 bits, the same seed (and thus the same keystream) repeats across frames fairly often in practice. When two frames are encrypted with the same keystream, XORing their ciphertexts cancels the keystream and leaves the XOR of the two plaintexts. With knowledge of some plaintext or by exploiting RC4 biases, an attacker can turn this into recovering plaintexts or the keystream itself, enabling further decryption of other frames. This reuse of the keystream from frames that effectively used the same key is the core weakness WEP attacks exploit, making the statement true.

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