Slovak University of Technology, Bratislava
Faculty of Electrical Engineering and Information Technology
Degree Course: INFORMATICS
Author: Branislav Jarábek
Diploma thesis: Generators of stream cipher based on inverse permutations
Supervisor: RNDr. Hana Lichardová, PhD.
December 2001

The subject of this thesis was to design and implement a system for generating a sequence of key stream of a stream cipher based on the inverse permutation. System also provides a possibility to verify generated sequences by means of universal statistic tests that are also included in the system.

Starting point for this work was streaming ciphers mathematical background analysis especially those ones based on permutations. There was analyzed a lot of cryptographic aspects of sequences in order to achieve the best possible parameters of designed generator. This thesis also points to a security aspect of the generated sequences. From this point of view is important to prevent all generated sequences from well?known basic attacks against the streaming ciphers.

Entire system was implemented in Linux operating system in C language with the use of special library for arbitrary precision arithmetic. System was designed to generate a part of sequence with the period, which is a large Sophie-Germain prime with selected number of bits. It provides a capability to test the final sequence by set of statistic tests, recommended by NIST organization and there is also designed and implemented an attack, which creates an alternate LFSR following the Berlekamp?Massey algorithm, which produces the same sequence.