Research On Application Of Hyperchaotic Encryption Combined With3DES In Secure E-Mail System

With the rapid development of computer networks and communication technology, moreand more information has been transmitted through the network. Many properties of chaoticsystems, such as non-periodic, randomness, broadband, sensitive dependence on initialconditions and unpredictability, are related to diffusion and confusion of cryptography.Therefore, chaos is very suitable in cryptography field.Chaotic system produce numerous, non-correlation, noise-like and pseudo-random chaossequence, the sequences are difficult to reconstruction and prediction. Recent research resultsshow that the nature and characteristic of low dimensional chaotic system can be conjecturedby phase space reconstruction. To enhance the security, using hyperchaotic is an effectivesolution. Besides, security of classical ciphers can be proved mathematically, so it issuggested that chaotic ciphers should be combined with classical ciphers to construct highlysecure cryptosystems.The work of this thesis is reflected in the following areas:(1) Based on hyperchaoticsequences, the encryption algorithm is improved. Firstly, the real chaotic sequences arepretreated, after pretreated the sequences have good uniform distribution, random statisticaland correlation properties. Secondly, through feedback perturbation to the system variable,speed up the non-correlation process, in order to meet the needs of quick response to the smalldifference of initial status and parameter in the hyperchaotic system. Lastly, through dividingthe interval to quantity generate more binary sequences, improving the speed and randomnessof sequence generation.(2) Evaluating the random performance of chaotic sequences withNIST test sofeware, choosing Frequency test, Block frequency test, Runs test, DFT spectraltest and Approximate entropy test to detect chaotic sequence. Result shows that improvedsequences have stronger pseudo-random.(3) A scheme of cascade cipher based improvedhyperchaotic sequences combined with3DES algorithm is proposed. This algorithm isapplied in Outlook2007E-mail system, realizing the security of email transmission. Theadvantages of classical and chaotic ciphers are fully utilized in cascade cipher algorithm. Thisalgorithm is characterized by large key space, high sensitivity to plaintext and key change,and strong resistance against statistical attacks and differential attacks. Besides, using theimproved chaotic sequence as3DES dynamic key, enhance the security of3DES algorithm.