On Effectiveness of Clock Control in Stream Ciphers

Shinsaku KIYOMOTO  Kazuhide FUKUSHIMA  Toshiaki TANAKA  Kouichi SAKURAI  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E90-A   No.9   pp.1780-1787
Publication Date: 2007/09/01
Online ISSN: 1745-1337
DOI: 10.1093/ietfec/e90-a.9.1780
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Information Theory and Its Applications)
stream cipher,  clock control,  irregular clocking,  

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In this paper, we examine the effectiveness of clock control in protecting stream ciphers from a distinguishing attack, and show that this form of control is effective against such attacks. We model two typical clock-controlled stream ciphers and analyze the increase in computational complexity for these attacks due to clock control. We then analyze parameters for the design of clock-controlled stream ciphers, such as the length of the LFSR used for clock control. By adopting the design criteria described in this paper, a designer can find the optimal length of the clock-control sequence LFSR.