A method for building a cryptographic generator of sequences with specified index of unrepeatability

It is known that iterative symmetric block ciphers may have a few specific keys termed “weak keys” and “semi-weak keys”. Due to this fact, we consider a method for constructing the key schedule providing the absence of duplication in round key sequence. For key generation, we propose the autonomous automaton based on one-two step generator consisting of two maximal period linear feedback shift registers of length $n$ and $m$. The output alphabet of this automaton is $V_m$ and the subsequence of length $2^{m-1}$ does not contain repeating vectors for any initial state of the automaton.