Fuzzy Logic-Based Security Evaluation of Stream Cipher

The main aim of this chapter is to provide a security evaluation method based on fuzzy logic “for a pseudo-random sequences used (mainly) in stream cipher systems. The designed Fuzzy rules consider two main parameters, which are the length of the maximum period of the key sequence obtained from Linear Feedback Shift Register (LFSR) and the entropy of the result in sequences obtained from different lengths of the shift registers. The security (complexity) evaluation method is applied to the summation generator (a type of non-linear feedback shift register) in this chapter. First it is applied to its original well-known form (with one bit memory); then the evaluation method is applied to the developed summation generator (by varying the number of the delayed bits by two and by three bits). The acceptability of the results of developed evaluation method indicates a goodness of such developed approach in the security evaluation.