Block image encryption based on modified playfair and chaotic system

Abstract

A new image encryption was done through using chaotic theory in the diffusion and confusion processes. Diffusion process was performed by using the chaotic cross map to permutate the matrix of each image color channel. Confusion process was implemented by a modified Playfair algorithm to generalize the classical one. Playfair algorithm divides the original text of characters into blocks, where each block usually contains two-character. The main limitations of Playfair cipher are that: it encrypts only 25 characters and one cannot use special characters and numbers. In addition, keyword can only take 25 letters alone without duplicates. The new method uses two cross chaotic maps to generate 16×16 playfair matrix as a key. The image is partitioned into a definite number of blocks such that each block has 16×16 bytes. Then, each block will be encrypted by different playfair matrix. All input data such as capital letter, small letter, digits and special characters, etc. can be encrypted by this new method. Experimental results showed that the proposed playfair cipher is more secure than the classical one and very sensitive to a slight change in the secret keys. The actual results of the encryption process showed that the proposed algorithm can defend against different attacks.