Research On Chosen Plaintext Attack For Plaintext-related Chaotic Image Encryption

The chaotic system has the characteristics of extremely sensitive to the initial values and parameters,aperiodic,the unpredictability of long-term evolution orbits etc.,and the image has the characteristics of the large data capacity,high redundancy,and high correlation between adjacent pixels etc.Therefore,chaos has been widely used in image encryption.Digital image encryption technology is widely used in the transportation field.For example,the calibrated road crack detection pictures have commercial value.Once the image information is illegally intercepted,tampered or even forged by hackers during the network transmission process,it will cause losses to customers or companies.The encryption algorithm based on chaotic system achieves good encryption effect.However,the existing image encryption schemes are not necessarily secure,and there are still security holes that can be attacked or deciphered by cryptanalysts.Therefore,this thesis focuses on cryptanalysis of two recently proposed plaintext-related image encryption algorithms,finds out the vulnerabilities of the algorithms,and improves the original algorithm to enhance the security of the original scheme.The main work and innovation of this thesis are as follows:(1)Focusing on the hidden security problems of a plaintext-related image encryption scheme based on a hyper-chaotic system has been proposed by Li et al.This thesis analyzes two vulnerabilities of Li's encryption scheme: 1)During the diffusion process,the gray values of the nine specific pixels do not change,that is,the pixel values of nine special pixels did not change before and after the diffusion;2)The permutation process is reversible,that is,the plaintext image can be obtained after applying the same permutation operation on the permuted image.Then,a selective plaintext attack scheme is proposed to crack the original scheme.Finally,the original algorithm is improved to solve the problem that the original algorithm cannot effectively resist the selection of plaintext attacks,and the security of the original scheme is enhanced.(2)Focusing on the issue that a pixel-level chaotic image encryption algorithm proposed by Ye et al.,There are security loopholes.This thesis analyzes two vulnerabilities of Ye's encryption scheme: 1)Both the rewriting and the diffusion operations are performed by modular addition,which can be equivalent to One-step equivalent diffusion operation,the effect of rewriting can be eliminated;2)The rewriting parameters and the diffusion matrix are both independent of the plaintext.Then,a selective plaintext attack scheme is proposed to crack the original scheme.Finally,some improvements for Ye's encryption scheme are provided to enhance the security.