  We study recovering parity check relations for an unknown code from
intercepted bitstream received from Binary Symmetric Channel in this paper. An
iterative column elimination algorithm is introduced which attempts to
eliminate parity bits in codewords of noisy data. This algorithm is very
practical due to low complexity and use of XOR operator. Since, the
computational complexity is low, searching for the length of code and
synchronization is possible. Furthermore, the Hamming weight of the parity
check words are only used in threshold computation and unlike other algorithms,
they have negligible effect in the proposed algorithm. Eventually, experimental
results are presented and estimations for the maximum noise level allowed for
recovering the words of the parity check matrix are investigated.
