Cryptanalysis Of A Class Of Plaintext-related Chaotic Image Encryption Schemes

The problem of network security,which is urgent today,has aroused with the improvement of Internet.More and more multimedia data have been uploaded to the network.As we know,the network is public and open,and everyone can access it.Therefore,there may be some illegal users intercepting or destroying the uploaded data.In order to protect the privacy,the technique of encryption has been widely used.Because digital image is one of the most important resources on the network,the research of image encryption is becoming hot.In this paper,we analyzed the new image encryption schemes,especially for the plaintext-related schemes,so as to make improvement.The main contents are listed below: First,study on a class of plaintext-related chaotic image encryption schemes,in which the characteristics of the plaintext can be found after image encryption.The security leakage of the plaintext-unrelated image encryption schemes has been analyzed.The advantages of plaintext-related image encryption schemes have been pointed out.Based on full investigation,the encryption model,as well as the attack model of the plaintext-related image encryption schemes leaking the plaintext characteristics has been proposed.Second,based on the proposed attack model,some cryptanalysis works have been made.The bit plane-based chaotic image encryption scheme is cryptanalyzed.The characteristics of plaintext can be found in the cipher text.Therefore,the plaintext can be chosen with the same property of the encrypted image to be attacked,and the equivalent key stream should be the same as that used in the target image.By analyzing the relationship between plaintext and cipher text,all the mappings can be found,instead of the secret keys.And the encryption scheme can be cracked by the mappings.Then,the butterfly-like chaotic image encryption scheme is cryptanalyzed by using the proposed attack model.Because the attacker knows the possibilities of the key parameter,he can try exhaust search to break the encryption scheme.The correct cracked result can be picked up from the 256 candidates by calculating the spatial correlation coefficients.The permutation and diffusion can also be broken by the method of finding mappings,showing that this method can be widely used.Third,an improved image encryption scheme has been proposed,in which the initial value of chaotic system is highly related to the plaintext,and the characteristics of plaintext cannot be found by the attacker either from the cipher text or from the algorithm.Experimental results(key space analysis,key sensitive analysis,histogram analysis,correlation analysis,information entropy analysis,resistance of differential attack)show that the proposed scheme resists chosen plaintext attack,and equips higher security.