Security Examination of a Cellular Automata Based Pseudorandom Bit Generator Using an Algebraic Replica Approach

A recently proposed scheme for key stream generators based on the programmable cellular automata and a read only memory is considered. It is shown that, the effective secret key size is significantly smaller than its formal length. The scheme is cryptanalyzed assuming ciphertext only attack, and novel cryptanalytic approach is proposed much more efficient than the reported one based on the known plaintext attack. As a development of the proposed basic algorithm for the secret key reconstruction the fast one is also given. Efficiency of the fast algorithm originates from the iterative error-correction procedure based on the algebraic replica approach.