27C3 - Version 1.6.3

27th Chaos Communication Congress
We come in peace

Martin Vuagnoux
Day Day 4 - 2010-12-30
Room Saal 2
Start time 17:15
Duration 01:00
ID 4261
Event type Lecture
Track Hacking
Language used for presentation English

News Key Recovery Attacks on RC4/WEP

In this paper, we present several weaknesses in the stream cipher RC4. First, we present a technique to automatically reveal linear correlations in the PRGA of RC4.

With this method, 48 new exploitable correlations have been discovered. Then we bind these new biases in the PRGA with known KSA weaknesses to provide practical key recovery attacks. Henceforth, we apply a similar technique on RC4 as a black box, i.e. the secret key words as input and the keystream words as output. Our objective is to exhaustively find linear correlations between these elements. Thanks to this technique, 9 new exploitable correlations have been revealed. Finally, we exploit these weaknesses on RC4 to some practical examples, such as the WEP protocol. We show that these correlations lead to a key recovery attack on WEP with only 9,800 encrypted packets (less than 20 seconds), instead of 24,200 for the best previous attack.

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