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1、云南大学数学与与统计学院上机实践报告一、实验目的理解古典密码学、统计分析攻击、信息熵与密码体制的关系二、实验内容1.古典密码体制Caesar密码的编程（参阅数据结构与算法主讲课教材的3.1.4节）2.任取一段较长的且有意义的英文片段，计算其明文熵。3.用Caesar密码加密上述英文片段，计算其密文熵。4.奔阅英文字母的频度分介规律，对上述密文进行统计分析攻击。三、实验环境个人计算机，Java平台对于非信息与汁算科学专业的宁生，可以选择任意编程平台四、实验记录与实验结果分析Caesar密码基本思想：通过把字母移动一定的位数来实现加密和解密。明文中的
2、所有字母都在字母表上向后（或向前）按照一个固定数H进行偏移后被替换成密文。例如，当偏移量是3的时候，所有的字母A将被替换成D,B变成E,以此类推X将变成A,Y变成B,Z变成C。由此可见，位数就是凯撒密码加密和解密的密钥。所选英文八段：Xi’anwasoncecalled‘‘Chang’an”intheHanDynasty.Theconnotationofthisnameis“permanentpeace”.Xi’anmarkedthestartingpointoftheworldfamousSilkRoad.Itobtaineditspresen
3、tnameintheyear1369.Xi’anranksfirstonthelistofthecountry’ssevenlargestancientcapitals.From11thcenturyB.C.onwards,andforaslongasmorethan1100years,Xi’anwassuccessivelyestablishedasthecapitalcityby15kingdomsorfeudaldynasties,includingtheWesternZhou,theQin,theHan,theSuiandtheTang.
4、Itservesasanancientcapitalcitybeyondcomparisonwithregardtothenumberofdynastiesandspanoftime.Anditwasregardedasoneofthe“FourAncientCapitalsoftheWorld”，theotherthreebeingRome,Athens,andIstanbul.运行结果：加密输入0,解密输入1:0明文字符串：Xi'anwasoncecalled‘‘Chang’an”intheHanDynasty.Theconnotationo
5、fthisnameis“permanentpeace”•Xi’anmarkedthestartingpointoftheworldfamousSilkRoad.Itobtaineditspresentnameintheyear1369.Xi’anranksfirstonthelistofthecountry’ssevenlargestancientcapitals.From11thcenturyB.C.onwards,andforaslongasmorethan1100years,Xi’anwassuccessivelyestablishedas
6、thecapitalcityby15kingdomsorfeudaldynasties,includingtheWesternZhou,theQin,theHan,theSuiandtheTang.Itservesasanancientcapitalcitybeyondcomparisonwithregardtothenumberofdynastiesandspanoftime.Anditwasregardedasoneofthe“FourAncientCapitalsoftheWorld”，theotherthreebeingRome,Athe
7、ns,andIstanbul.移动位数：3所得密文为：str=ATdqzdvrqfhfdoohg“Fkdqj’dq”lqwkhKdqGbqdvwb.Wkhfrqqrwdwlrqriwklvqdphlv“shupdqhqwshdfh”•ATdqpdunhgwkhvwduwlqjsrlqwriwkhzruogidprxvVIonUrdg.Lwrewdlqhglwvsuhvhqwqdphlqwkhbhdu1369.Al’dqudqnviluvwrqwkholvwriwkhfrxqwub’vvhyhqodujhvwdqflhqwfdslwdov.Iurp
8、1lwkfhqwxubE.F.rqzdugv,dqgirudvorqjdvpruhwkdq1100bhduv,Al'dqzdvvxffh
