Conference Paper

Mutually Clock-Controlled Feedback Shift Registers Provide Resistance to Algebraic Attacks.

DOI: 10.1007/978-3-540-79499-8_17 Conference: Information Security and Cryptology, Third SKLOIS Conference, Inscrypt 2007, Xining, China, August 31 - September 5, 2007, Revised Selected Papers
Source: DBLP

ABSTRACT 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.