This study proposes a self-adaptive image encryption algorithm based on the quantum logistic map. First, the initial values are substituted into the quantum logistic map based on an iteration process to generate three random sequences. After preprocessing, three new random sequences with better randomicity were obtained from the generated random sequences. In particular, the correlation coefficients for random sequences before and after preprocessing are compared to determine the best model to make the correlation coefficients closer to zero. Second, one random sequence in the scrambling stage is selected with respect to the plain image. The selected random sequence is then used to perform row-column perturbation on the plain image. Finally, the remaining two random sequences are used to perform forward and reverse diffusion to obtain the final cipher image. Because of the dependence on the plain image, the algorithm can frustrate the chosen-plaintext and known-plaintext attacks. Experimental results show that the proposed encryption algorithm can achieve secure communications.

A visually meaningful image encryption scheme with an asymmetric structure based on the discrete wavelet transform (DWT) and Schur decomposition is proposed in this study. First, the RSA algorithm is used to generate the initial values for the chaotic system to produce the random sequence. Then, both scrambling and diffusion operations are performed on the plain image to obtain the preencrypted image. Moreover, the Schur decomposition is applied on the preencrypted plain image to obtain the upper triangular and orthogonal matrices. Second, the cover image is scrambled followed by a DWT operation. Four subbands are then formed, namely, LL, HL, LH, and HH. Finally, the former upper triangular matrix and orthogonal matrix are embedded into subbands LH and HH produced by the cover image. After the application of the inverse DWT and inverse scrambling operation, the final visually meaningful cover image embedded with a secret plain image can be obtained. No one can identify any useful information about the plain image from the final embedded cover image, nor can anybody know that there is any hidden secret image. Experimental simulations show that the normalized correlation values between the original cover image and the final visually meaningful cover image are approximately 0.9997. Therefore, the proposed encryption scheme is imperceptible for secret image communications.

We propose a new asymmetric pixel confusion algorithm for images based on the Rivest-Shamir-Adleman (RSA) public-key cryptosystem and Arnold map. First, the RSA asymmetric algorithm is used to generate two groups of Arnold transform parameters to address the problem of symmetrical distribution of Arnold map parameters. Second, the image is divided into blocks, and the first group of parameters is used to perform Arnold confusion on each sub-block. Then, the second group of parameters is used to perform Arnold confusion on the entire image. The image correlation is thereby fully weakened, and the image confusion degree and effect are further enhanced. The experimental results show that the proposed image pixel confusion algorithm has better confusion effect than the classical Arnold map based confusion and the row-column exchange based confusion. Specifically, the values of gray difference are close to one. In addition, the security of the new confusion operation is dependent on RSA, and it can act as one part of a confusion-substitution structure in a cipher.

This study proposes a new image encryption scheme based on a generalized Arnold map and Rivest–Shamir–Adleman (RSA) algorithm. First, the parameters of the generalized Arnold map are generated by an asymmetric encryption-system RSA algorithm, and the keystream is produced iteratively. To change the distribution of pixel values, the image data are hidden by XOR diffusion. Second, both rows and columns of the image are cyclically confused to hide the image data again. Then, the additive mode diffusion operation is performed to realize third-layer hiding for image content. The overall diffusion and confusion operations are conducted twice to obtain the final cipher image. Test results prove that the encryption scheme proposed in this study is effective and has strong antiattack capabilities and key sensitivity. In addition, because the scheme security relies on the RSA algorithm, it has high security.