A Technique for Securing Multiple Digital Images Based on 2D Linear Congruential Generator, Silver Ratio, and Galois Field

Security of multiple digital images over an unsecured channel is a current area of research in the field of image cryptography. Several techniques have been proposed for this purpose. However, the main drawbacks of the existing techniques are as follows: the existing techniques can be applied merely to the grayscale or the truecolor images; the size of the cipher (output) image is bigger than that of the plain (input) images; the authors have used a large number of parameters in the encryption/decryption process, besides the secret key; and the cipher/decipher rounds use the same key for encryption/decryption process. The proposed technique, which is based on a two-dimensional (2D) Linear Congruential Generator (LCG), silver ratio, and Galois field, is designed not merely to secure multiple digital images, namely, three truecolor, nine grayscale, and seventy-two binary images of different sizes, simultaneously, but also to address the above drawbacks. The designed technique achieves both confusion and diffusion properties essential for a secure cryptosystem. Also, the technique is empirically assessed via several statistical and security evaluation metrics, such as key sensitivity, histogram, chi-square, entropy, number of pixel change rate, structural similarity index measure, processing time, etc. The results of these evaluation metrics prove the efficiency and robustness of the designed technique.