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Cisco Wireless LAN Security by Andrew Balinsky, Darrin Miller, Krishna Sankar, Sri Sundaralingam

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WEP Keystream and Plaintext Recovery

There are two means of breaking WEP-encrypted data. The most obvious is to discover the key itself. The other is to discover all possible keystreams that a key can generate. This section deals with recovering and using keystreams. The section titled “WEP Key Recovery Attacks” deals with how to crack the keys. Attack Trees 3 and 4 (from earlier in this chapter) show that recovering the key or the keystream enables reading and writing of encrypted data.

RC4 encryption involves XORing the keystream (K) with the plaintext (P) data to produce the ciphertext (C). If an attacker knows any two of these three elements, he can calculate the third. An attacker can always know C because it is broadcast. Thus, if an attacker ...

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