The Design And Application Of The Stream Cipher Algorithm Based On Chaos And RC4

With the rapid development of computer and internet technology, it is necessary to develop safe, effective and reliable encryption technology to meet the safety requirements of information. The chaotic system is complex in dynamics, hard to estimate the long-term behavior, sensitive to initial conditions and able to create massive high security sequence with high performance in cryptography, so it seems very suitable for modern cryptography.Therefore, in this thesis, the chaotic system is applied to the encryption algorithm, and two kinds of algorithms are proposed. The performance of two algorithms is tested from several aspects. Moreover, the two algorithms are applied to image encryption. The main efforts of the thesis are as follows:1)Due to the chaos degradation caused by limited precision effort in chaos system, an pseudo-random sequence generator based on spatiotemporal chaos mapping is designed and an pseudo-random sequence generator based on variable parameter multistage chaos system is created. The property of sequence generated by the two pseudo-random is evaluated from three aspects as follows: cycle length, correlation, NIST statistic testing. Experiment shows that the pseudo-randomness of the sequences is excellent.2)A improved sequence encryption algorithm called CS-RC4 is developed based on the combination of chaos s-box and RC4 algorithm, which generate initial key by the chaos mapping and use the unpredictability of chaos orbit to destroy the dynamic regularity of s-box in RC4 algorithm. the safety of CS-RC4 is enhanced.3)Another improved sequence encryption algorithm called SC-RC4 based on spatiotemporal chaos system and RC4 algorithm is proposed. The new algorithm make a xor operation between the spatiotemporal chaotic key stream and plaintext data at first, and then encrypt the processed data by RC4 algorithm under the control of 128 bit chaos key.Compared with RC4 algorithm, it has the higher security.4)We implement encryption and decryption of image through using the CS-RC4 and SC-RC4 algorithms respectively. Then evaluate the two algorithms from six aspects: greylevel histogram, adjacent pixels correlation, key space, key sensitivity, encryption speed and computational cost. Experiments shows that the two improved algorithms both have high security and high encryption speed. To verify the practicability of CS-RC4 and SC-RC4 algorithms, a mobile phone application about chaos image encryption is designed with user-friendly control, high security, as well as high encryption speed.