Geodesic
A method for building a~cryptographic generator of sequences with specified index of unrepeatability
Prikladnaya Diskretnaya Matematika. Supplement, no. 9 (2016), pp. 65-67.

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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.
Keywords: block cipher, round key, $r$-unrepeatable sequence, $r$-unrepeatable automaton, index of unrepeatability. 
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     author = {D. A. Romanko and V. M. Fomichev},
     title = {A method for building a~cryptographic generator of sequences with specified index of unrepeatability},
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D. A. Romanko; V. M. Fomichev. A method for building a~cryptographic generator of sequences with specified index of unrepeatability. Prikladnaya Diskretnaya Matematika. Supplement, no. 9 (2016), pp. 65-67. http://geodesic.mathdoc.fr/item/PDMA_2016_9_a25/

[1] Fomichev V. M., Metody diskretnoi matematiki v kriptologii, Dialog-MIFI, M., 2010, 424 pp.