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 twocharacter. 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 16xc3x9716 playfair matrix as a key. The image is partitioned into a definite number of blocks such that each block has 16xc3x9716 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.

A Bijective Image Encryption System Based on Hybrid Chaotic Map Diffusion and DNA Confusion Modern multimedia communications technology requirements have raised security standards, which allows for enormous development in security standards. This article presents an innovative symmetric cryptosystem that depends on the hybrid chaotic Lorenz diffusion stage and DNA confusion stage. It involves two identical encryption and decryption algorithms, which simplifies the implementation of transmitting and receiving schemes of images securely as a bijective system. Both schemes utilize two distinctive nonconsecutive chaotic diffusion stages and one DNA scrambling stage in between. The generation of the coded secret bit stream employs a hybrid chaotic system, which is employed to encrypt or decrypt the transmitted image and is utilized in the diffusion process to dissipate the redundancy in the original transmitted image statistics. The transmitted image is divided into eight scrambled matrices according to the position of the pixel in every splitting matrix. Each binary matrix is converted using a different conversion rule in the Watsonxe2x80x93Crick rules. The DNA confusion stage is applied to increase the complexity of the correlation between the transmitted image and the utilized key. These stages allow the proposed image encryption scheme to be more robust against chosenknown plaintext attacks, differential attacks, cipher image attacks, and information entropy. The system was revealed to be more sensitive against minimal change in the generated secret key. The analysis proves that the system has superior statistical properties, bulkier key space, better plain text sensitivity, and improved key sensitivity compared with former schemes.