Method for designing pseudorandom binary sequences generators on Nonlinear Feedback Shift Register (NFSR) Dr. N.G BARDIS Department of Automation Technological Education Institutes of Halkis 34400 Psahna, Halkis, Evia, Greece Dr. A.P. MARKOVSKYY Department of Computer Engineering National Technical University of Ukraine 37, Peremohy, pr. Kiev 252056, KPI 2003, Ukraine D.V. ANDRIKOU, MSc Telecommunications and Computer Science Engineer GREECE Abstract: - This paper presents a new method for designing effective nonlinear pseudorandom bits generator for data security systems. The proposed method allows that design of n-bits Nonlinear Feedback Shift Registers (NFSR), which ensure the repeat cycle of 2 n . In contrast to Linear Feedback Shift Registers (LFSR) the pseudorandom sequences whish are generated by NFSR cannot be predicted if 2⋅n bits of the sequence are known. A generator, designed by the proposed method ensures the high performance and effectiveness of hardware realization. Key-Words: - NonLinear Feedback Shift Register (NFSR), pseudorandom binary sequences generators 1 Introduction The dynamic development of the information integration based on telecommunication and computer networks techniques is closely linked with extending the use of the pseudorandom binary sequences. Such sequences are widely used in CDMA and cosmic telecommunication systems, in digital data transmission channels for error detecting and error correcting, in VLSI embedded self- monitoring devices and in data security systems. In contemporary situations where the integration of information expands and the increase of productivity of computer systems which can be used to attack data security components the problem of guaranteeing data security is acquiring a great importance. This problem can be solved by way of perpetually developing data security methods and techniques, including pseudorandom sequence generators. Basically they are an important class of cryptographic algorithms, which are called stream ciphers algorithms. Apart from this, pseudorandom binary sequence generators are widely used to form keys and they are important components of cryptographic protocols and one-way hash functions. The main sphere of pseudorandom sequence generators is utilized in stream cipher algorithms. This class of algorithms ensures the greatest cryptographic coding rate and is oriented for real- time data security systems. So, the stream cipher algorithms are widely used for cryptographic coding of video and voice telecommunications, telemetry and telecontrol systems. From this point of view, one of the most important criterions of pseudorandom sequence generator is the effectiveness of bits generation rate. Another important criterion of pseudorandom sequence generator is the level of crypto-resistance which is characterized by the sample size of sequence forecasting. Most part from modern pseudorandom binary sequence generators is build with Linear Feedback Shift Registers (LFSR), which ensure a repeat of sequence period of 2 n -1 (n- bits length of shift register) and the effectiveness of hardware implementation. The main disadvantage of LFSR utilization is that the binary sequence generated by the LFSR can easily be forecasted if a sample size of 2⋅n bits is known (in case the feedback linear function is unknown). Therefore, in real sequence generators it is necessary to use additional nonlinear transformation which increases the complexity and reduces the generation rate [2, 3]. The Nonlinear Feedback Shift Register (NFSR) does not have the above mentioned disadvantage of the LFSR and the utilization of NFSR ensures a significant increase of the crypto - resistance level of pseudorandom bits sequence. Today there is no mathematical common theory for NFSR design [4,5,6,7]. Thus only one possible way for NFSR practical implementation consists of the development of the particular approaches for the NFSR designing.