An efficient cryptanalysis of a chaotic cryptosystem and its improvement

Recently, a new block encryption system has been proposed based on iterating a logistic map. This paper studies the security of the new encryption scheme and reports the following findings: (1) the sub-keys of any ciphertext can be obtained by using only two chosen ciphertexts; (2) the underlying chaotic key stream sequence can be reconstructed as an equivalent key by some chosen plaintext and ciphertext pairs. Experimental results are given to demonstrate the feasibility of the proposed attacks. Furthermore, a remedial improvement is suggested, which avoids the flaws while keeping all the merits of the original cryptosystem.