  In this paper, a new image encryption scheme using a secret key of 144-bits
is proposed. In the substitution process of the scheme, image is divided into
blocks and subsequently into color components. Each color component is modified
by performing bitwise operation which depends on secret key as well as a few
most significant bits of its previous and next color component. Three rounds
are taken to complete substitution process. To make cipher more robust, a
feedback mechanism is also applied by modifying used secret key after
encrypting each block. Further, resultant image is partitioned into several key
based dynamic sub-images. Each sub-image passes through the scrambling process
where pixels of sub-image are reshuffled within itself by using a generated
magic square matrix. Five rounds are taken for scrambling process. The propose
scheme is simple, fast and sensitive to the secret key. Due to high order of
substitution and permutation, common attacks like linear and differential
cryptanalysis are infeasible. The experimental results show that the proposed
encryption technique is efficient and has high security features.
