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This paper analyzes the security issues of the recently proposed image encryption scheme based on paired interpermuting planes. The permutation process of the scheme is designed to permute the pixel values between colour channels and in the diffusion process, the function value of previous cipher is xored to the current pixel, where the function is a permutation map. For a single round encryption/decryption, the chosen plaintext/ciphertext attack is performed to find the permutation map and the keys of the permutation process. A modified scheme is proposed in which the permutation is done in two stages, within the colour channel using generalised cat map and between the colour channels that depends on the values of the pixel after the permutation within the colour channel. The diffusion process chooses the xoring value based on the previous pixel cipher value and the pixel location. These processes are designed to overcome the weaknesses identified and the to resist the chosen plaintext/ciphertext attack. [ABSTRACT FROM AUTHOR]

This paper analyzes the security issues of the recently proposed JPEG image encryption scheme. A new image encryption algorithm using modified logistic map is proposed. The chaotic sequences generated using modified logistic map are used for permutation, bit swapping and random diffusion. These processes impose the confusion and diffusion effect on the image and make the scheme secure. The security parameters such as entropy, correlation, NPCR and UACI are tested and the results show the scheme is secure. [ABSTRACT FROM AUTHOR]

Abstract: In recent years, a number of chaos-based image cryptosystems have been proposed to meet the increasing demand for real-time secure image transmission. In this paper, an improved diffusion scheme named continuous diffusion strategy is proposed to promote the efficiency of the conventional permutation–diffusion type image cipher. The new scheme contains a supplementary diffusion procedure after the conventional diffusion process and the control parameters are altered by the cipher image after the first diffusion procedure. As a result, the difference can be introduced at the beginning and spread out to the whole image, and hence the same level of security can be achieved with fewer overall rounds. Moreover, to further enhance the confusion effect of the diffusion operation, an intensive diffusion approach is proposed, using stretched key stream elements to perform a cyclic shift to the cipher pixels. Extensive cryptanalysis has been performed using differential analysis, key space analysis, key sensitivity analysis and various statistical analyses. Experiment results demonstrate that the new scheme has a high level of security and fast encryption speed for practical image encryption. [Copyright &y& Elsevier]