This paper deals with the image encryption scheme based on non-linear dynamic chaotic system in stream cipher architecture. The narrowing of the numbers domain interval to [0.2, 0.8] and a double precision floating point format to encode float numbers to binary format were used for pseudo random stream generator. The results of the NIST statistical test suite and security analysis are given. The results show very good cryptographic properties and high security. Key-Words: Image encryption, Non-linear chaotic dynamic system, Stream generator, Security analysis, Cryptography.

This paper deals with the original construction of the cryptographic secure pseudo random number generator based on non-linear dynamic chaotic system. The narrowing of the numbers domain interval to [0.2, 0.8] and a double precision floating point formatting to encode float numbers to binary format were used for getting pseudo random bits. The results of the second level NITS tests for randomness of the proposed pseudo random bit generator (PRBG) are presented. They testify very good cryptographic properties of the proposed PRBG.

Modulation impulse shaping in conventional communication systems usually is realized by the root-raised-cosine filtering. Recently modulation impulse shaping on the basis of wavelet transform was proposed. The present paper deals with the use of quasiorthogonal sequencies for impulse shaping. The main objective is to design the SIMULINK models of communication systems with modulation impulse shaping on the basis of quasi-orthogonal sequencies, wavelets and root-raised-cosine filters and to evaluate the nonlinear amplification sensitivity and the performance of systems corrupted by noise. The main results are: the systems with quasiorthogonal sequences require more bandwith, the performance of them is is some what less and non-linear amplification sensitivity of them is notibly less comparing with other systems. Ill. 16, bibl. 7 (in Lithuanian; summaries in English, Russian and Lithuanian).