Image encryption is the most direct and effective technical means for protecting the security of image information. Based on the space filling property of the Hilbert curve and the infinite property of the H-geometric fractal, a new image encryption technique is proposed, which combines the pseudo-randomness of a hyperchaotic system and the sensitivity to initial values. First, the hash value of a plaintext image is calculated using the Secure Hash Algorithm 3 (SHA-3) as the initial value of the piece-wise linear chaotic map (PWLCM) and Rossler chaotic systems, which associates the key with the plaintext. In addition, the chaotic sequences that are generated by the chaotic systems are used to scramble the global pixel positions and the pixel values of the images, thereby disturbing the distribution of the pixel positions and the pixel values. Second, the Hilbert curve and H-fractal are alternately used to scramble the local pixel positions and diffuse the pixel values twice. Finally, the ciphertext feedback is used to further enhance the confusion and diffusion characteristics of the algorithm in order to achieve higher security. The experimental results and security analysis show that the encryption technique has enough key space to resist exhaustive attacks and can effectively resist statistical attacks, differential attacks, noise attacks and cropping attacks. It can be used for military, judicial, and other privacy-related digital image secure storage and network security transmissions.

To enhance the security of image data transmission, and address the weaknesses of existing image encryption schemes based on chaotic systems, particularly concerning resistance to differential attacks and the unstable performance of chaotic systems, this article introduces an improved four-dimensional chaotic system and integrates evolutionary operators to propose an image encryption scheme. Firstly, a method for generating pseudo-random sequences associated with the plaintext is designed. The change rate of the ciphertext pixel value exceeds 0.9967 after a slight modification of the plaintext pixel value, significantly improving the plaintext sensitivity and the scheme's ability to resist selected plaintext attacks. Secondly, an individual rearrangement operation is introduced to achieve bit-level scrambling, and pixel-level scrambling is achieved by selection strategy. Subsequently, crossover and mutation operations are incorporated into image encryption. To reflect the randomness of the pairing, we adopt the pseudo-random sequence generated by the chaotic system to control the crossover and mutation operators, and a diffusion operation is performed on selected pixel pairs. Finally, ciphertext feedback is applied. Experimental results and performance analysis demonstrate that the proposed scheme not only enhances the security of encrypted images but also effectively resists noise and cropping attacks. This method effectively meets the high-security requirements of images in network transmission and provides new ideas for further research in the field of image encryption.

Based on the Feistel network and dynamic DNA encoding technology, an image encryption method is proposed using the "permutation-diffusion-scrambling" structure. First, the SHA-3 algorithm is used to calculate the hash value of the plaintext image as the initial value of the hyper-chaotic system, and the chaos-generated sequence is used to generate the Hill cipher matrix to replace the image pixel. Second, the DNA sequence operation is used as the F function of the Feistel network. The DNA sequence database is used as the key K of Feistel network, and the image pixel value diffusion is realized by the Feistel network. Finally, further diffusion is carried out through the ciphertext feedback and through the ciphertext confusion and diffusion of three rounds of "chaotic scrambling-DNA encoding-Feistel transformation-DNA decoding", making the ciphertext more random and resistant to attacks and ensuring that the encrypted ciphertext is more secure. The experimental results show that the proposed method can effectively encrypt the image and has prominent characteristics, such as strong plaintext sensitivity, a large key space and excellent ciphertext statistical properties.

The vast parallelism, exceptional energy efficiency and extraordinary information density inherent in DNA molecules are being explored for computing, data storage and cryptography. DNA cryptography is a new field of cryptography arising with the research of DNA computing in recent years. In this paper, an encryption scheme is designed by using the technologies of DNA synthesis, PCR amplification and DNA digital coding as well as the theory of traditional cryptography. By applying the special function of primers to PCR amplification, the primers and coding mode are used as the key of the scheme. The traditional encryption method and DNA digital coding are used to preprocess to the plaintext, which can effectively prevent attack from a possible word as PCR primers. Biological difficult issues and cryptography computing difficulties provide a double security safeguards for the scheme. And the security analysis shows that the encryption scheme has high confidential strength. To demonstrate the performance, we present an interesting example to encode and decode message just between specific two persons using the proposed scheme.