The Design And Implementation Of E-mail Encryption System Based On Chaotic

With the rapid development of computer networks and communication technology, E-mail has become an important application. And most of e-mails transmit information through plaintext, it may bring about information security problems. Chaos has some special properties which make a natural relationship with cryptography, such as sensitive to initial conditions, non-periodic, etc. Recently, designing some chaotic encryption algorithms which is used to secure communication has become a focal topic for research. In traditional cryptography algorithms, although symmetry encryption has a high encryption speed, its key space is very small and will be break easily; asymmetry encryption algorithm has the advantages of complexity and large key space, but its speed is low and not suitable for encryption of enormous attachments. Compared to traditional encryption algorithms, chaotic streamcipher encryption algorithms have some properties such as high encryption speed, high sensitive to initial conditions, large key space and so on, which can improve the anti-attack of cryptography. This paper studies the design and implementation of e-mail encryption which based on chaotic, the main work of this paper includes:(1) Studying the basic theory of chaos, based on the noted Sprott system, a new and modified chaotic system can be constructed with change equation coefficient. And the dynamical behavior of the modified chaotic system is further investigated, including: symmetry, the balance point, stability, Lyapunov exponents'spectrum, and bifurcation analysis. Besides, the analog circuits of the modified system is designed on EWB, experimental results show that the attractors of the modified chaotic system are the same with which emulation by MATLAB ,which verifies the nature of chaotic system.(2) Studying the basic theory of cryptography, and introducing several classification method of cryptography. Several designing ideas based on chaotic system are summed and described through analyzing and comparing the relationship between cryptography and chaotic from different angles. Chaotic cryptography will be applied in the field of network security communications which lay the theoretical foundation in the future.(3) In order to implement the PR sequences, the continuous systems are discredited and quantized into theoretical model. Then, FPGA development board developed by Altera, DSP Builder, MATLAB/Simulink and Quartus II, are used to implenting chaotic sequences. And the attractors obtained through D/A conversion are same with the emulation result.(4) The performance of PR sequences plays an important role in cryptography security, so evaluate the performance of chaotic sequence is important for a chaotic cryptosystem. Now the popular method is use NIST (National Institute of Standards and Technology) to test sequences, it includes 15 test indexes. Experimental results show that the PR sequences successfully passes the statistical tests.(5) Through analyzing and comparing various traditional encryption algorithms, e-mail encryption system is designed and implemented which based on chaotic system. At the same time, three measures including key sensitivity analysis, key space, and encryption speed analysis are used to analysis the performance of e-mail encryption system. The results show that the proposed e-mail encryption software has some properties such as large key space, high encryption speed, sensitive to initial conditions, and convenience of key management.