Chaotic systems perform well as a new rich source of cryptography and pseudo-random coding.Unfortunately their digital dynamical properties would degrade due to the finite computing precision.Proposed in this paper is a modified digital chaotic sequence generator based on chaotic logistic systems with a coupling structure where one chaotic subsystem generates perturbation signals to disturb the control parameter of the other one.The numerical simulations show that the length of chaotic orbits,the output distribution of chaotic system,and the security of chaotic sequences have been greatly improved.Moreover the chaotic sequence period can be extended at least by one order of magnitude longer than that of the uncoupled logistic system and the difficulty in decrypting increases 2 128 2 128 times indicating that the dynamical degradation of digital chaos is effectively improved.A field programmable gate array (FPGA) implementation of an algorithm is given and the corresponding experiment shows that the output speed of the generated chaotic sequences can reach 571.4 Mbps indicating that the designed generator can be applied to the real-time video image encryption.
