International Association for Cryptologic Research
Irregular clocking of feedback shift registers is a popular technique to improve parameters of key-stream generators in stream ciphers. Another technique is to implement nonlinear functions. The authors join these techniques and propose modified alternating step generators built with linear and nonlinear feedback shift registers. Adequate nonlinear boolean functions are used as feedbacks or as filtering functions of shift registers in order to increase complexity of sequences produced by individual registers and the whole generator.