This paper puts forward a novel image encryption scheme based on ordinary differential equation system. Firstly, a hyper-chaotic differential equation system is used to generate two hyper-chaotic orbit sequences. Introducing the idea of hybrid orbit, two orbits are mixed to generate a hybrid hyper-chaotic sequence which is used to be the initial chaotic key stream. Secondly, the final encryption key stream is generated through two rounds of diffusion operation which is related to the initial chaotic key stream and plain-image. Therefore, the algorithm’s key stream not only depends on the cipher keys but also depends on plain-image. Last but not least, the security and performance analysis have been performed, including key space analysis, histogram analysis, correlation analysis, information entropy analysis, peak signal-to-noise ratio analysis, key sensitivity analysis, differential analysis etc. All the experimental results show that the proposed image encryption scheme is secure and suitable for practical image and video encryption.

A secure image encryption scheme based on 2D skew tent map is proposed for the encryption of color images. The proposed encryption scheme is composed of one permutation process and one substitution process. The 3D color plain-image matrix is converted to 2D image matrix first, then 2D skew tent map is utilized to generate chaotic sequences, which are used for both permutation process and substitution process. The chaotic sequence for permutation process is dependent on plain-image and cipher keys, resulting in good key sensitivity and plaintext sensitivity. The substitution process is first initiated with the initial vectors generated by the cipher keys and 2D skew tent map, then the gray values of row and column pixels of 2D image matrix are mixed with the pseudorandom number sequences via bitxoring operation. Both permutation process and substitution process are executed row-by-row and column-by-column instead of pixel-by-pixel to improve the speed of encryption. The security and performance of the proposed image encryption have been analyzed, including histograms, correlation coefficients, information entropy, key sensitivity analysis, key space analysis, differential analysis, encryption/decryption rate analysis etc. All the experimental results suggest that the proposed image encryption scheme is robust and secure and can be used for secure image and video communication applications.

A novel image encryption scheme based on chaotic system is proposed. The proposed encryption scheme utilizes one tent map to generate a pseudo-random sequence and then shift the bits of the expanding 0-1 image circularly so as to shuffle the image gray values. To make the encryption scheme resist differential attack efficiently, generalized Arnold maps and Bernoulli shift maps are applied to produce two pseudo-random gray value sequences and then diffuse the gray values bi-directionally. The bit circular shift process and diffusion processes greatly confuse the statistical nature between plain-images and cipher-images. Security analyses including key sensitivity analysis, key space analysis, statistical analysis, differential attack analysis and information entropy analysis are performed. All the experimental results demonstrate that the proposed image encryption scheme possesses large key space to frustrate brute-force attack efficiently and can resist statistical attack, differential attack, etc.