# linear feedback shift register (LFSR)

A Linear FeedbackShift Register (LFSR) is a shift register with linear feedback. Here, the data signal is shifted one position further through the shift register with each clock pulse. For the feedback mechanism, some outputs of the flip-flops are linked in an XOR gate whose output is fed to an input of a flip-flop. Linear feedback shift registers are ideal as random number generators for generating statistical random numbers. The only signal they require is a clock signal.

Linear feedback shift registers are used to generate pseudorandom numbers, pseudorandom noise, and in fast counting circuits. For example, in synchronouscurrent ciphers, the key current is generated by a Linear Feedback Shift Register (LFSR). The key current is calculated using a linear feedback function. Such a register consists of several logics that are set by an initialization vector, which is usually the secret key. The behavior of the registers is controlled by the clock signal, and each time the clock signal changes state, the register contents are advanced by one logic. With this procedure, a bit is generated as an output signal with each clock signal change.