Explanation of Shrinking and Self-Shrinking Generators

Question

Give a brief explanation of Shrinking and Self-Shrinking Generators.

Answer 1

The shrinking generator was intended by Coppersmith, Mansour, and Krawczyk. It is a stream cipher which is based on simple interaction between the outputs from two LFSRs. The bits of one output are employed to verify whether the corresponding bits of second output will be employed as part of the whole keystream. The shrinking generator is simple and scalable, and has better security properties. One demerit of shrinking generator is that the output rate of keystream will not be stable unless precautions are taken. A variant of shrinking generator is self-shrinking generator, where rather than using one output from one LFSR to ‘shrink’ the output of another (as in shrinking generator), the output of the single LFSR is employed to extract bits from the same output. There are as yet no results on cryptanalysis of either method.