Given a 0-1 matrix M the matrix reordering problem is to find  a matrix M ' obtained by permuting the columns of M that minimizes Cr(M ' ) the number of sequences of consecutive ones in M ', this problem is NP hard.,
In this paper, we give a solution of the matrix reordering problem for special cases and we  present  a new modified version of McEliece cryptosystem  using the hardness of this problem.