The Design And Implementation Of An Encryption Algorithm Based On Alternant Chaotic Sequence

Chaotic encryption is an arisen research subject in recent years. Chaotic mapping has good properties, that it can obtain two entirely different sequences after a few times' iteration on the closely same initial conditions; it is unable to forecast the next numerical value according to the sequence itself; and the generated sequences equiprobably distribute on the range. All of these good properties make chaotic encryption fit for sequence encryption.The key point of design for the sequence encryption algorithm based on chaotic system is the selection of chaotic mapping. Various chaotic mappings are different in complexity of algorithm realization, time and space complexity of the algorithms and security. Logistic is a typical one-dimensional chaotic mapping whose realization algorithm is simple and operation speed is fast. However, its key space is smaller and security is worse. Three-dimension chaotic Lorenz system which is more popular has more complex realization algorithm and slower operation speed, but its key space is bigger and security is higher.In order to increase the security of chaotic encryption algorithm without affecting the operation efficiency, this dissertation proposes a method in which the two chaotic cipher sequences are generated based on the Logistic mapping and tent mapping, and then the plaintexts are encrypted alternately. Compared with encryption algorithm of using Logistic mapping alone, this method has bigger key space and simpler dynamical equation because of the combination of Logistic mapping and tent mapping, thus the operation of computer is only the simple basic ones. In addition, its encryption speed is the same as that of Logistic. This paper does a research on the security of the algorithm in three ways: randomness, linear complexity and intensity of the initial key. The result shows that this method can completely meet the security demand of modern cryptology.Besides, this method is simple to be realized by software. This paper develops the software design of the chaotic encryption using Visual C++ which has many advantages, such as friendly interface, easy operating, good practicability and high security.