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The original computer applications usually had no or fewsecurity, because the systems of then were exclusive and close,in a brief,though computers did exchange the data and information,the network formed was completely under control by theirorganization. At that time, the communication protocols betweencomputers is not public either, preventing others to access theinformation exchanged. Thus the information secure was not aproblem then and the situation lasted for many years, till datasecurity was realized.In nowadays, the information society, the research ofcommunication secure is not only required for military, politicalor diplomacy use, but also in research of science and techniqueor commerce. Therefore information is compared to life, time andwealth. Due to the sharing and pervasion of information wouldgreatly affect the society, so to keep information security is anemergency in information time. Along with the history flowing into21st Century, information security is more and more highlyrequired, and the protection of information security is more andmore highly expected.Nowadays, as information security is regarded as the importantproblem by the society, Cryptography is paid more and moreattention. Cryptography mainly cares about secrecy incommunication. Encrypting the transmitting data could preventothers from stealing important information, but this only solvesthe problem on the one hand, as for how to prevent them fromdestroying important data, to ensure the dealer identification orto abstain denying when dissension is occurred would be additionalproblems. We apply digital signature in use. Digital signature isa further application beyond data encryption. Digital signatureis always companioned with Hash functions, which is a kernel ofmodern Cryptography. The most common Hash methods are MD5, SHA andSnefru. MD5 is a typical Hash encryption technique and it is quitepopular. In the paper we made a research on MD5 to optimize therealization.The full name of MD5 is Message-Digest Algorithm 5. It is ahash algorithm to generate digital signatures. MD5 is irreversiblearithmetic, which means doing reversing to cipher text will leadto infinitude reverses. It was proposed at the beginning of 90’sby Ronald L. Rivest from MIT Laboratory for Computer Science andRSA Data Security Inc, through MD2, MD3 and MD4. The algorithm wasdesigned to compress big block of information to a secret formbefore signing with private key, which is to transform a randomlength bit sequence with an irreversible string to a certain lengthof 128 bit big integer. In other words, having seen the source codeand the algorithm description, one still cannot function backwardsfrom a MD5 value to the original sequence. MD5 is widely used inelectric business, encryption and decryption, information login,database and file system integrity.After getting to know MD5, we introduce the MD5 main functionto realize the testing program of file manipulation. We also adda timing function to record the time cost for manipulation, so asto obtain MD5 manipulate rate according to different file size.As we all know, two important parameters to value an encryptionfunction is the intensity and the speed. The encryption intensityis the basic essence of encryption arithmetic and the abilityagainst varies attacks. In most applications, beyond certainencryption intensity, encryption/decryption speed is the mostimportant property, especially for high speed required systems.The encryption speed is determined originally by the design of analgorithm, but it can be optimized by using varies tips to bringthe potential into play. In the 3rd chapter of the paper, on thebase of behavior analysis with the MD5, we gave some effectiveoptimizing methods for MD5 algorithm, such as outspreadingencryption circulation, collaboration and paralleling optimizing,memory copy optimizing, reducing iterating times, optimizingarray diversion functions, embedding compilation language andaccommodating different operation systems. We also gave out theexample of optimizing and the measure result, on the platform ofIntel Pentium 4CPU/WindowsXP/IE 6.0. The result shows the speedof MD5 algorithm was for sure improved by the application ofoptimizing methods.During the course of analyzing and optimizing the MD5 algorithm,we learned that varies encryption algorithms, computer conditions,compilers and operation systems could all impact on the speed, sowe must determine suitable strategy in applying optimizing methodsso as to improve speed to the greatest extent.
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