Description of non-endomorphic maximum perfect ciphers with two-valued plaintext alphabet

This paper deals with non-endomorphic perfect (according to Shannon) ciphers, which are absolutely immune against the ciphertext-only attacks in the case when plaintext alphabet consists of two elements. Matrices of probabilities of cipher keys are described in terms of linear algebra on the basis of Birkhoff's theorem (about the classification of doubly stochastic matrices). The set of possible values of a priori probabilities for elements in ciphertext alphabet of a perfect cipher is constructed.