Abstract   In this work the use of nonlinear filtering functions applied to Linear Feedback Shift Registers (LFSRs) to generate cryptographic sequences has been studied. Emphasis is on the class of equivalent nonlinear filter generators whose elements produce exactly the same sequence. Given a pair (filtering function, LFSR), the work develops a method of computing equivalent filtering functions applied to different LFSRs, where all these filters generate exactly the same cryptographic sequence. The security of a cipher is that of its weakest equivalent. Thus this article allows one to compute weaker equivalents of apparently secure generators.
['Amparo Fúster-Sabater', 'Sara D. Cardell']
Cryptographic Properties of Equivalent Ciphers