Distinguishing attacks on stream ciphers based on arrays of pseudo-random words

In numerous modern stream ciphers, the internal state consists of a large array of pseudo-random words, and the output key-stream is a relatively simple function of the state. In [16], it was heuristically shown that in various cases this structure may lead to distinguishing attacks on the cipher. In this paper we further investigate this structural attack. We present a rigorous proof of the main probabilistic claim used in the attack in the basic cases, and demonstrate by examining a concrete example (the cipher sn3 [11]) that the heuristic assumptions of the attack are remarkably precise in more complicated cases. Furthermore, we use the general technique to devise a distinguishing attack on the stream cipher mv3 [9] requiring 282 words of key-stream. Unlike the attacks in [16], our attack does not concentrate on the least significant bits of the words, thus allowing to handle the combination of more operations (xors, modular additions and multiplications, and rotations by a fixed...

• Type: Journal
• Year: 2010
• Where: IPL
• Authors: Nathan Keller, Stephen D. Miller
• Keywords: Cipher, Distinguishing Attack, IPL 2010, Stream Cipher