Cryptanalysis of the BBCRS system on Reed-Muller binary codes

The paper considers the BBCRS system which is a modification of the McEliece cryptosystem proposed by M. Baldi and some others. In this modification matrix of the public key is the product of three matrices: a non-singular -matrix , a generator matrix of a secret -code , and a non-singular -matrix . The difference between the modified system and the original system is that the permutation matrix used in the McEliece system is replaced by a non-singular matrix . The matrix is obtained as the sum of a permutation matrix and a matrix of small rank . Later, V. Gauthier and some others constructed an attack that allows decrypting messages in the case when is a generalized Reed-Solomon code (GRS code) and . The key stages of the constructed attack are, firstly, finding the intersection of the linear span and that spanned on the rows of the matrices and respectively, and secondly, finding the code by the subcode . In this paper we present an attack in the case when is the Reed-Muller binary code of order , length and . The stages of finding the codes and in this paper are completely different from the corresponding steps in attack by V. Gauthier and some others and other steps are the adaptation of the known results of cryptanalysis that applied in the case of GRS codes.