Decimation attack on nonlinear feedforward sequences

The feedforward sequence is decomposed into the modulo 2 adders of decimation sequences whose decimation distance is the first element of cyclotomic cosets in linear feedback shift register (LFSR) sequence by using the trace representation of feedforward function. Then the corresponding decimation sequences are eliminated one by one with recursive formulas of all decimation sequences, and until one decimation sequence of LFSR sequence is worked out. Finally, the initial state of LFSR can be recovered according to the decimation sequence.