WEP was previously known to be insecure. In 2001 Scott Fluhrer, Itsik Mantin, and Adi Shamir published an analysis of the RC4 stream cipher. Some time later, it was shown that this attack can be applied to WEP and the secret key can be recovered from about 4,000,000 to 6,000,000 captured data packets. In 2004 a hacker named KoReK improved the attack: the complexity of recovering a 104 bit secret key was reduced to 500,000 to 2,000,000 captured packets. In 2005, Andreas Klein presented another analysis of the RC4 stream cipher. Klein showed that there are more correlations between the RC4 keystream and the key than the ones found by Fluhrer, Mantin, and Shamir which can additionally be used to break WEP in WEP like usage modes.
We were able to extend Klein's attack and optimize it for usage against WEP. Using our version, it is possible to recover a 104 bit WEP key with probability 50% using just 40,000 captured packets. For 60,000 available data packets, the success probability is about 80% and for 85,000 data packets about 95%. Using active techniques like deauth and ARP re-injection, 40,000 packets can be captured in less than one minute under good condition. The actual computation takes about 3 seconds and 3 MB main memory on a Pentium-M 1.7 GHz and can additionally be optimized for devices with slower CPUs. The same attack can be used for 40 bit keys too with an even higher success probability.
http://www.cdc.informatik.tu-darmstadt.de/aircrack-ptw/
Erik Tews, Andrei Pychkine and Ralf-Philipp Weinmann are cryptographic researchers at the cryptography and computer algebra group at the technical university Darmstadt in Germany. Head of the group is Prof. Dr. Dr. Johannes Buchmann.
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