ENHANCED CRYPTANALYSIS OF A CLOCK–CONTROLLED RUNNING KEY GENERATOR

Milan Vojvoda

   One simple running key generator which combines the outputs of two asynchronously clocked LFSRs has been proposed in [15]. In this paper the period of the keystream and several theorems concerning the number of runs in a ml-sequence are proved. Conditions for passing the Golomb’s randomness postulates are proposed. Results of applied statistical tests (FIPS 140-1, gap test, serial correlation test) are presented. Finally, a modification of the generator using substitution of FCSRs (feedback with carry shift registers) for LFSRs is studied.

Keywords: stream cipher, running key generator

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