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Aircrack-ng is a network software suite consisting of a detector, packet sniffer, WEP and WPA/WPA2-PSK cracker and analysis tool for 802.11 wireless LANs.It works with any wireless network interface controller whose driver supports raw monitoring mode and can sniff 802.11a, 802.11b and 802.11g traffic.
Network encryption cracking is the breaching of network encryptions (e.g., WEP, WPA, ...), usually through the use of a special encryption cracking software. It may be done through a range of attacks (active and passive) including injecting traffic, decrypting traffic, and dictionary-based attacks.
A 128-bit WEP key is usually entered as a string of 26 hexadecimal characters. 26 digits of 4 bits each gives 104 bits; adding the 24-bit IV produces the complete 128-bit WEP key (4 bits × 26 + 24-bit IV = 128-bit WEP key). Most devices also allow the user to enter it as 13 ASCII characters (8 bits × 13 + 24-bit IV = 128-bit WEP key).
WEP used the RC4 algorithm for encrypting data, creating a unique key for each packet by combining a new Initialization Vector (IV) with a shared key (it has 40 bits of vectored key and 24 bits of random numbers). Decryption involved reversing this process, using the IV and the shared key to generate a key stream and decrypt the payload.
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.
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.
WEP was superseded in 2003 by WPA, a quick alternative at the time to improve security over WEP. The current standard is WPA2; [3] some hardware cannot support WPA2 without firmware upgrade or replacement. WPA2 uses an encryption device that encrypts the network with a 256-bit key; the longer key length improves security over WEP.
The first public release of Crack was version 2.7a, which was posted to the Usenet newsgroups alt.sources and alt.security on 15 July 1991. Crack v3.2a+fcrypt, posted to comp.sources.misc on 23 August 1991, introduced an optimised version of the Unix crypt() function but was still only really a faster version of what was already available in other packages.