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Published in:
2008 | OriginalPaper | Chapter
Mutually Clock-Controlled Feedback Shift Registers Provide Resistance to Algebraic Attacks
Authors : Sultan Al Hinai, Lynn Margaret Batten, Bernard Colbert
Published in: Information Security and Cryptology
Publisher: Springer Berlin Heidelberg
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Algebraic attacks have been applied to several types of clock-controlled stream ciphers. However, to date there are no such attacks in the literature on mutually clock-controlled ciphers. In this paper, we present a preliminary step in this direction by giving the first algebraic analysis of mutually clock-controlled feedback shift register stream ciphers: the bilateral stop-and-go generator, A5/1, Alpha 1 and the MICKEY cipher. We show that, if there are no regularly clocked shift registers included in the system, mutually clock-controlled feedback shift register ciphers appear to be highly resistant to algebraic attacks. As a demonstration of the weakness inherent in the presence of a regularly clocked shift register, we present a simple algebraic attack on Alpha 1 based on only 29 keystream bits.