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How Secure Is Your Wireless Network? Safeguarding Your Wi-Fi LAN by CCNA Lee Barken - CISSP MCP, CPA

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Decrypting the WEP Message

Decryption is the same process as encryption, but in reverse. We take the IV (which is sent in clear text) and prepend it to the secret key and plug that into the RC4 cipher to regenerate the key stream. Next, we XOR the key stream with the cipher text, which will give us the plain text value. Finally, we reperform the CRC-32 checksum on the message and ensure that it matches the integrity check value in our decrypted plain text. If the checksums do not match, the packet is assumed to have been tampered with and discarded.

Where Do IVs Come From?

One of the flaws in the implementation of the RC4 cipher in WEP is the fact that the 802.11 protocol does not specify how to generate IVs. Remember that IVs are the 24-bit ...

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