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2008)“On the security of a class of Image Encryption Scheme
 Department of Electronics Engineering, University of Hong Kong
"... Abstract — Recently four chaosbased image encryption schemes were proposed. Essentially, the four schemes can be classified into one class, which is composed of two basic parts: permutation of position and diffusion of pixel value with the same ciphertext feedback function. The operations involved ..."
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Abstract — Recently four chaosbased image encryption schemes were proposed. Essentially, the four schemes can be classified into one class, which is composed of two basic parts: permutation of position and diffusion of pixel value with the same ciphertext feedback function. The operations involved in the two basic parts are determined by a pseudo random number sequence (PRNS) generated from iterating a chaotic dynamic system. According to the security requirement, the two basic parts are performed alternatively for some rounds. Although the designers claimed that the schemes are of high quality, we found the following security problems: 1) the schemes are not sensitive to the changes of plainimages; 2) the schemes are not sensitive to the changes of the key streams generated by any secret key; 3) there exists a serious flaw of the diffusion function; 4) the schemes can be broken with no more than ⌈log L (MN)⌉+3 chosenimages when the iteration number is equal to one, where MN is the size of the plainimage and L is the number of different pixel values; 5) the cryptanalysis on one scheme proposed by another research group is questionable. I.
On the security of an image encryption scheme
"... This paper studies the security of a recentlyproposed image encryption scheme based on chaos, and points out the following problems: 1) there exist a number of invalid keys and weak keys, and some keys are partially equivalent for the encryption/decryption processes; 2) given one chosen plainimag ..."
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This paper studies the security of a recentlyproposed image encryption scheme based on chaos, and points out the following problems: 1) there exist a number of invalid keys and weak keys, and some keys are partially equivalent for the encryption/decryption processes; 2) given one chosen plainimage, a subkey K10 can be guessed with a smaller computational complexity than that of the simple bruteforce attack; 3) given O(10) (at most 128) chosen plainimages, a chosenplaintext attack may be able to break the following part of the secret key: ({Ki mod 128}9i=4,K10), which works very well when K10 is not too large; 4) when K10 is relatively small, a knownplaintext attack can be mounted with only one known plainimage to recover some visual information of other plainimages encrypted by the same key. Key words: cryptanalysis, image encryption, chaos, knownplaintext attack, chosenplaintext attack 1