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In Shared Key authentication, the WEP key is used for authentication in a four-step challenge–response handshake: The client sends an authentication request to the access point. The access point replies with a clear-text challenge. The client encrypts the challenge-text using the configured WEP key and sends it back in another authentication ...
Injecting traffic means inserting forged encrypted messages into the network. It may be done if either the key is known (to generate new messages), or if the key is not known and only an encrypted message and plaintext message is gathered, through comparison of the two. Programs able to do the latter are Aireplay and WepWedgie.
To prevent this from happening, WEP includes a 24-bit initialization vector (IV) in each message packet. The RC4 key for that packet is the IV concatenated with the WEP key. WEP keys have to be changed manually and this typically happens infrequently. An attacker therefore can assume that all the keys used to encrypt packets share a single WEP key.
TKIP employs a per-packet key, meaning that it dynamically generates a new 128-bit key for each packet and thus prevents the types of attacks that compromised WEP. [ 4 ] WPA also includes a Message Integrity Check , which is designed to prevent an attacker from altering and resending data packets.
Weak PSK passphrases can be broken using off-line dictionary attacks by capturing the messages in the four-way exchange when the client reconnects after being deauthenticated. Wireless suites such as aircrack-ng can crack a weak passphrase in less than a minute. Other WEP/WPA crackers are AirSnort and Auditor Security Collection. [25]
Stream ciphers are vulnerable to attack if the same key is used twice (depth of two) or more. Say we send messages A and B of the same length, both encrypted using same key, K. The stream cipher produces a string of bits C(K) the same length as the messages. The encrypted versions of the messages then are: E(A) = A xor C E(B) = B xor C
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In cryptography, a pre-shared key (PSK) is a shared secret which was previously shared between the two parties using some secure channel before it needs to be used. [ 1 ] Key