Chapter: Cryptography and Network Security

Linear Feedback Shift Register (LFSR)

An LFSR of length m consists of m stages numbered 1, 2, . . . ,m, each storing one bit and having one input and one output; together with a clock which controls the movement of data.

LINEAR FEEDBACK SHIFT REGISTER (LFSR)

An LFSR of length m consists of m stages numbered 1, 2, . . . ,m, each storing one bit and having one input and one output; together with a clock which controls the movement of data.

The vector (k1, k2, · · · , km) would be used to initialize the shift register. During each unit of time the following operations would be performed concurrently

k1 would be tapped as the next keystream bit

k2, · · · , km would each be shifted one stage to the left

the “new” value of km would be computed to be

the linear feedback is carried out by tapping certain stages of the register (as specified by the constants cj having the value “1”) and computing a sum modulo 2 (which is an exclusive-or).

Applications:

· Pseudo-random number

· Pseudo-noise sequences

· Digital counters

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Cryptography and Network Security : Linear Feedback Shift Register (LFSR) |