Research On Digital Chaos Encryption

In this thesis, the background of digital chaotic encryption technology is introduced firstly. Then, Baptista-type chaotic cryptosystem has been carefully studied and new scheme has been proposed accordingly. The main research conents and originality of this thesis can be summarized as follows:Firstly, to solve the two major drawbacks of Baptista-type chaotic cryptosystem, the lower bound of the expectation of the cipher-to-plaintext ratio is worked out by the entropy of the ciphertext. The approximation formula is presented to calculate the expectation of bitO ratio of ciphertext. To improve the efficiency of Baptista-type cryptosystem, the plaintext-block size is analytically influnenced upon its lower bound and the encryption time, the Truncated Huffman coding (THC) is introduced to approximately reach the lower bound. Numerical paradigms prove the validity.Secondly, double look-up table based search mechanism chaotic cryptosystem is proposed, the pretreatment to the plaintext is performed with the Baptista-type Look-up Table (BLUT). With the definition of New-type Look-up Table (NLUT), the pretreated plaintext is encrypted. And the approximation formula is presented to calculate the expectation of bitO ratio of ciphertext. Then combining the expectation of cipher-to-plaintext ratio, the scheme is optimized by adjusting the length of NLUT. It is from experiments that the scheme results in higher security and better ciphertext characteristic.Finally, to settle the dynamical degradation of digital chaos, a control character based chaotic scheme is introduced. Firstly, iterate the chaotic system; the control character is produced according to the chaotic state. The pretreatment to the plaintext is performed with the control character. Then the plaintext after pretreatment is encrypted by the look-up table. Meanwhile, the look-up table is updated according to the control character continuously. Otherwise, the chaotic trajectory is changed continuously according to the control character, which enhances the security of the scheme ulteriorly. At last, analysis and experiments prove the validity of the scheme.