  The Hill cipher is a classical symmetric encryption algorithm that succumbs
to the know-plaintext attack. Although its vulnerability to cryptanalysis has
rendered it unusable in practice, it still serves an important pedagogical role
in cryptology and linear algebra. In this paper, a variant of the Hill cipher
is introduced that makes the Hill cipher secure while it retains the
efficiency. The proposed scheme includes a ciphering core for which a
cryptographic protocol is introduced.
