Andrew Klapper Jinzhong Xu Register Synthesis for Algebraic Feedback Shift Registers Based on Non-Primes. 227-250 2004 31 Des. Codes Cryptography 3 http://dx.doi.org/10.1023/B:DESI.0000015886.71135.e1 db/journals/dcc/dcc31.html#KlapperX04