Design criteria and security evaluations on certain stream ciphers

摘要

This paper shows design criteria and security evaluations on nonlinear filter generators (NFGs), a kind of linear feedback shift register (LFSR)-based keystream generators. For the LFSR, two types of configurations are available - a standard LFSR and a modular LFSR. From the point of hardware operation speed, the modular LFSR is preferable. On the contrary, the standard LFSR-based NFGs have high level security by Golic's design criteria. A state transformation matrix is introduced, which translates characteristics of one type NFGs to another. We proposed new design criteria on the modular LFSR-based NFGs, and found their security level nothing less than Golin's, by evaluating with the state transformation matrix.