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Medical images contain a large amount of patients' private information. The theft and destruction of medical images will cause irreparable losses to patients and medical institutions. In order to detect the region of interest(ROI) accurately, avoid leakage of ROI position information, and realize lossless recovery of transform domain encryption, we propose a novel lossless medical image encryption scheme based on game theory with optimized ROI parameters and hidden ROI position. In the encryption process, the ROI is a pixel-level transformed to achieve the lossless decryption of medical images and protect medical image information from loss. At the same time, the position information of the ROI is effectively hidden, and leakage of the position information during transmission is avoided. In addition, the quantum cell neural network(QCNN) hyperchaotic system generates random sequence to scramble and diffuse the ROI. Most important of all, the quantitative analysis method of ROI parameters is given, and the optimal balance between encryption speed and encryption security performance is achieved by using game theory. Simulation experiments and numerical analysis verify that the scheme achieves optimized and lossless encryption and decryption of images, and can flexibly and reliably protect the medical images of different types and structures against various attacks.

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Both symmetric and asymmetric color image encryption have advantages and disadvantages. In order to combine their advantages and try to overcome their disadvantages, chaos synchronization is used to avoid the key transmission for the proposed semi-symmetric image encryption scheme. Our scheme is a hybrid chaotic encryption algorithm, and it consists of a scrambling stage and a diffusion stage. The control law and the update rule of function projective synchronization between the 3-cell quantum cellular neural networks (QCNN) response system and the 6th-order cellular neural network (CNN) drive system are formulated. Since the function projective synchronization is used to synchronize the response system and drive system, Alice and Bob got the key by two different chaotic systems independently and avoid the key transmission by some extra security links, which prevents security key leakage during the transmission. Both numerical simulations and security analyses such as information entropy analysis, differential attack are conducted to verify the feasibility, security, and efficiency of the proposed scheme.

In order to guarantee the security of digital images, image encryption is a good tool. This paper puts forward a novel image encryption/decryption algorithm based on bit-level permutation and dynamic overlap diffusion. Firstly, location information set by users is used to scramble the plain image in the bit-level, changing the pixel position of the image while changing the pixel value. Then, using the plaintext related method to control the iteration parameters of Arnold transform. These two parts together form the permutation process of the algorithm. Thirdly, the overlap steps are set according to the encryption security requirements, and dynamic overlap diffusion is performed on the permutation image. At the same time, the plaintext information entropy and variance are used to update the diffusion key in the fivedimensional hyperchaotic system to achieve the plaintext correlation of the encryption key. Arnold transform and dynamic overlap diffusion can ensure that different key streams are generated when encrypting different images. Finally, experimental analysis and numerical simulation show that our algorithm has high efficiency, high security, high sensitivity, and can effectively resist various attacks.INDEX TERMS bit-level permutation, dynamic overlap diffusion, hyperchaotic system, image encryption, plaintext related key