Digital Image Encryption Using Improved Hill Cipher Method

Abstract

Images are widely used in the world for different purposes. So, the risk of image sharing is increasing. Because, when images are sharing through unsecured networks unauthorized users can easily hack to images. Therefore, image encryption is more important for users to maintain privacy. In this paper we propose an algorithm to encrypt images by using Self-Invertible Matrix of Hill Cipher method. It is one of the symmetric techniques. We used a self- invertible 4×4 matrix as the secret key and the novelty of this method is to separate the original image pixel values into blocks of size four by four. The advantage of the proposed method is that it has simple steps, no need to find the inverse of the key matrix in the decryption process. In this study, the arithmetic operations of modular arithmetic addition, subtraction, multiplication and division were used to generate the self-invertible matrix for the Hill cipher algorithm. Size 64×64 Baboon, Lenna, Tree color images were used in this study. MATLAB software was used for computational experiments. Moreover, it needs a little time for image encryption. This proposed algorithm has high efficiency than other Hill cipher techniques. To ensure the security of our encryption method, several widely used measures are considered here, including speed analysis, histogram analysis technique, Unified Average Changing Intensity (UACI) and Number of Pixel Changing Rate (NPCR) analysis.