Cryptanalysis and Improvement of a Chaotic Map-Control-Based and the Plain Image-Related Cryptosystem

Due to the characteristics of chaotic systems, different cryptosystems based on chaos have been proposed to satisfy the security of multimedia data. A plain image-related chaotic algorithm is proposed by Luo et al. with high speed and efficiency. Security weaknesses of the cryptosystem are studied in this paper. It is found that the important secret key information is leaked because an important parameter can be obtained after an inverse operation in the last step of the cryptosystems without secret key. Meanwhile, the value zero is processed improperly in quantification algorithm. Based on the weaknesses, chosen plaintext attack on the cryptosystem is proposed, by which, an important parameter, equivalent to secret key, can be calculated with a specific chosen plain image. With the obtained parameter, the plain image of any ciphered image, encrypted by the cryptosystem, can be recovered. Then, an improvement is proposed to solve the problems after modifying the quantification algorithm. It is from the experiments that chosen plaintext attack is valid and improved algorithm possesses better performance.