Abstract:
Many cryptosystems were designed to prevent
data from unauthorized access, and some are
relatively secure but slow. Others are fast but
relatively not secure enough. One of the most
efficient cryptosystems is Hill Cipher algorithm
which is classified as symmetric encryption. In
this paper we provide a solution for the problem
of non-invertible matrix by modifying the way of
dealing with key matrix, and make all matrices;
including not invertible ones, usable in modified
Hill cipher system. Moreover, it will solve the
known of pair plaintext and cipher text problem
by generating new key matrix for each encrypted
block of plaintext, using SHA-512. Since SHA-
512 generates 64 integers we can manipulate
these integers to become 128 different integers
and use them as an input for the matrix; based on
the concept that any acceptable data must not be
prime.
