| With the vigorous development of the Internet,the amount of data and information transmitted on the network is also exploding.Image is one of the main forms of expression of data information.Once it is stolen or destroyed by lawbreakers,it can bring huge economic losses at a slight scale,and threaten national security in serious cases.Therefore,designing a safe and effective encryption algorithm for digital images has important academic significance and practical application value.In this paper,chaos system and DNA coding technology are used as the starting point,two encryption algorithms are designed for gray image and color image,and performance evaluation experiments are carried out on them.The main contents are as follows:（1）Aiming at the shortcomings of the image encryption algorithm using static DNA encoding that it is easy to be cracked by brute force,a gray image encryption algorithm based on dynamic DNA encoding is proposed.Based on the excellent Standard Map,two sets of keys are used to iterate the chaotic sequence to expand the key space of the encryption algorithm,and the SHA-256 function is introduced to further improve the security of the key.The algorithm uses an image encryption framework of scrambling diffusion.In the scrambling phase,the Fisher-Yates shuffling algorithm is improved,so that it can be applied to pixel scrambling.In the diffusion stage,the scrambled image is dynamically encoded with DNA,and then the diffusion based on the DNA XOR operation is performed,and finally the ciphertext image is obtained through the DNA dynamic decoding.In order to further improve the encryption strength,two linear operations based on image block,translation and rotation,are designed before and after the scrambling and diffusion stage.Experimental analysis from multiple angles shows that the information entropy and sensitivity data of this algorithm are close to ideal values,and are more prominent than other algorithms.（2）Aiming at the shortcomings of insufficient security of a single chaotic system,a color image encryption algorithm based on a hybrid chaotic system is proposed.The hybrid chaotic system used is composed of Tinkerbell map and 4D hyperchaotic system.This paper analyzes and improves the performance of the former.The algorithm first uses the SHA-384 function to obtain the digest of the plaintext image,and uses it to adjust the parameters in the key,so that the algorithm can resist the equivalent key attack.Secondly,a new concept of high and low level grayscale images is proposed,and different algorithms are used to complete image scrambling for reconstructed images of different complexity.Finally,based on DNA dynamic encoding and decoding,a set of unique DNA encoding operation rules is designed,and the image after scrambling has completed two-way diffusion between the R,G and B channels and within the channel.Through multiple experiments,it is verified that the key space of this algorithm reaches 2558;the information entropy of Lena ciphertext image reaches7.9973;and the NPCR and UACI values are close to the theoretical values,and the sensitivity is good;the performance of the algorithm is better than some other methods. |
