On the efficiency of the Clock Control Guessing Attack.
Erik Zenner · 2002
Many bitstream generators are based on linear feedback shift registers. A widespread technique for the cryptanalysis of those generators is the linear consistency test (LCT). In this paper, we consider an application of the LCT in cryptanalysis of clock-controlled bitstream generators, called clock control guessing. We give a general and very simple method for estimating the eciency of clock control guessing, yielding an upper bound on the e ective key length of a whole group of bitstream generators. Finally, we apply the technique against a number of clock-controlled generators, such as the A5/1, alternating step generator, step1-step2 generator, cascade generator, and others.