Analysis of Baptista-Type Chaotic Cryptosystem

To solve the two major drawbacks of Baptista-type chaotic cryptosystem - excessive length of ciphertext and unbalance frequency of bit 0 to bit 1, the lower bound of the expectation of the cipher-to-plaintext ratio is worked out by the ciphertext entropy, and the approximation formula is presented to calculate the expectation of bit 0 frequency of ciphertext. In order to improve the efficiency of Baptita-type cryptosystem, the plaintext-block size is analytically influenced upon its lower bound and the encryption time, then N-truncated Huffman coding is introduced into the scheme so as to approximately reach the lower bound. Numerical paradigms prove the validity of the analysis.