  A During last two decades, there has been a prolific growth in the chaos
based image encryption algorithms. Up to an extent these algorithms have been
able to provide an alternative to exchange large media files (images and
videos) over the networks in a secure way. However, there have been some issues
with the implementation of chaos based image ciphers in practice. One of them
is reduced/small key space due to the fact that chaotic behavior is only
observed for certain range of system parameters/initial conditions of the
chaotic system used in such algorithms. To overcome this difficulty, we propose
a simple, efficient and robust image encryption algorithm based on combined
applications of quasigroups and chaotic standard map. The proposed image cipher
is based on the popular substitution-diffusion architecture (Shanon) where a
quasigroup of order 256 and chaotic standard map have been used for the
substitution and permutation of image pixels respectively. Due to the
introduction of quasigroup as part of the secret key along with the parameter
and initial conditions of the chaotic standard map, the key space has been
increased significantly. The proposed image cipher is very fast due to the fact
that the substitution based on the quasigroup operations is very simple and can
be executed easily through the lookup table operations on Latin squares (which
are Cayley operation tables of quasigroups) and the permutation is performed
row-by-row as well as column-by-column using the pseudo random number sequences
gener-ated through the chaotic standard map. The security and performance have
been analyzed through the histograms, correlation coefficients, information
entropy, key sensitivity analysis, differential analysis, key space analysis
etc. and the results prove the efficiency and robustness of the proposed image
cipher against the possible security threats.
