Design and analysis of chaotic map and chaotic key based encryption algorithms for digital images

Abstract

The availability and increased usage of multimedia applications has led features such as compression and security gain considerable importance. Digital images are used in many applications such as defense, space, medicine, industry and education. Secure storage and transmission of digital images are essential to avoid major threats and attacks. Cryptography plays an important role in protecting sensitive images from theft and alteration. Conventional data encryption techniques cannot be used on images due to the inherent features of the images such as bulky data, redundancy and high correlation among pixels. Discrete chaotic map based image encryption schemes are most popular in view of their excellent features such as extreme sensitivity to small variations in initial conditions, ergodicity and unpredictability. One of the popular one-dimensional chaotic maps used in the literature is the logistic map considering its low computational cost and simplicity. The focus of this research work is on three major objectives. The first objective is to construct a novel key generation algorithm and to realize a computationally secure double image cryptosystem that possesses combined encryption and compression characteristics and also a single image encryption scheme without compression. The second objective is to design a onedimensional chaotic map suitable for cryptographic applications and to mathematically and experimentally prove the existence of chaos in the designed chaotic map. The third objective is to construct an authenticated secure image cryptosystem using a novel integer-based key generation algorithm designed using a proposed chaotic map and to compare and analyze the encryption algorithms with the existing techniques. In the first part of the research, a key generation algorithm was proposed and a double image symmetric encryption scheme with combined compression and encryption was constructed. The keys used for encryption process have been generated using a novel modified convolution and chaotic mapping technique. First, the four most significant bits of the two images were extracted and combined after permutation employing the proposed logistic mapping. Also, cellular automata based diffusion was performed on the resultant image to strengthen the security further. In this work, both confusion and diffusion have been integrated thereby improvising the encryption scheme. Since two images are compressed and encrypted simultaneously, it is useful in real - time scenarios. Also, a single image encryption scheme without compression was proposed. The test of randomness of the key and the performance results for the proposed single image and double image encryption algorithms were found to be successful. These algorithms provide good robustness to occlusion and noise attack. Therefore, the proposed algorithms can be used for both storage and image newline