Most practical key stream generators are based on shift registers. The shift register has a simple structure and a fast running speed. However, with primitive polynomials, linear feedback shift registers can generate sequences that appear random and have very long cycle periods. Moreover, because the state of the register is limited, it will eventually be a repeated cycle. The initial value assigned to the register is called the "seed", because the operation of the linear feedback shift register is deterministic, so the data stream generated by the register is completely determined by the state of the register at that time or before. The four shift units in the circuit are all composed of dynamic master-slave edge-type flip-flops, and each shift operation requires data to pass through two stages of latches in sequence. In the shift unit of this structure, the master-slave two-pole latch, under the control of the two-phase non-overlapping clock, causes the data to be sampled on the rising edge of the clock and is held until the next rising edge of the clock.
The shift unit in the linear feedback shift register is composed of a master-slave edge trigger.
Therefore, a higher speed can be obtained. Its upper limit shift speed depends on the delay time of the shift unit and the delay time of the two-input XOR gate. The characteristic of this circuit is its simple structure. The two-input XOR gate is used to calculate the characteristic polynomial of the maximum or near maximum length of the feedback function without rectifying the register. Its characteristics are usually characterized by a characteristic polynomial. Linear feedback shift register (LFSR) is usually composed of dynamic or static master-slave flip-flop. The famous sequence and sequence are generated by linear and nonlinear feedback shift registers, respectively. It is divided into two categories: linear and nonlinear. The shift register is a common device for generating signals and sequences.
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