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Nonlinear System as a Stream-Cipher

A new stream cipher based on a nonlinear system. The scheme follow the structure of a Nonlinear-feedback Shift Register (NLFSR). However, it does not exhibit the cryptographic drawbacks as the NLFSR does such as an unpredictable maximal period of the generated sequences, insufficient randomness level and high probability of falling in a static state. The proposed stream uses a secret key of lentgh 256-bit and generates a keystream of length 16-bits in each iteration. The produced output sequences are pseudorandom. That means that they cannot be distinguished from a random sequence and the cipher can resist to common stream-cipher attacks like the distinguishing attack, SAC-r Diffusion test and SAC-c Diffusion test, algebraic attack and correlation analysis. Moreover, the proposed cipher surpass the AES standard and Rabbit cipher in term of encryption-decryption total time.