密码破译问题中的Mathmatic

密码破译问题中的Mathmatic 数 学 实 验 化机0603丁悦 200642058 数学实验 密码破译问题中的Mathmatic 实验名称:单表代替密码破译 问题背景描述:去年初夏，情节跌宕起伏的电视剧《暗算》成了荧屏的一大亮点，其中片子 的第二部《看风》主要是反映破译密码的，《看风》向我们展示的是最困难 的“唯密文攻击”，也就是破译者所能获得的仅仅是密文，这种情况对于破译 者是极其严酷的考验。对于一部设计良好的密码，“唯密文攻击”难如登天～ 对于破译者来说，该部密码的内部结构如果是已知条件，当然对破译出密钥 是一个极大的帮助。如果情况并非如此，则能部分得到密文所对应的明文也 是好的。( 实验目的:通过Mathmatic软件对一组单表代替密码英文文档进行了 实验所用软件和版本:,athematica5.2 实验过程记录(基本步骤，主要程序清单及异常情况记录): 根据大量统计资料,英文中字母出现的相对频率如下: 英文中字母的相对频率 14 12 10 8 6 4 2 0 abcdefghijklmnopqrstuvwxyz 不仅单字母以相对稳定的频率出现,而且双字母组和三字母组同样如此.出现频率最高的 30个双字母组依次是:th he in er an re ed on es st en at to nt ha nd ou ea ng as or ti is et it ar te se hi of ;出现频率最高的三字母组依次是:the ing and her are ent tha nth was eth for dth hat she ion int his sth ers ver. 统计文本文件(" Wzss I pdbyzh xdksy lj wzWczb I pvi yhzvelba vwdkj tdk wvwtYdk pzhz yhzvelba dp ezCvss ez xhvotCvss ez wslbyTd ijlss wz ikppzhlba li ijkfly vpjzh vss dp jcli jlezDly I sdiz et sdnz jd idezdbz wzjjzhAby ydzi icz sdnz tdk sluz I ydI yd, tdk ubdp I hzvsst hzvsst ydWzss cztSd ekxc I bzzy jd ivtBzzb sdbzst ilbxz jcz yvtTcz yvt tdk pzbj vpvtSd ivy wkj jhkzFdh ez jczhz'i dbst tdkBzzb xhtlba ilbxz jcz yvtTcz yvt tdk pzbj vpvtI hzezewzh yvjz vby jlezSzfjzewzh jpzbjt izxdbySkbyvt jpzbjt plnz vpjzh blbzIb jcz yddhpvt pljc tdkh xvizNd sdbazh icdkjlba vj zvxc djczhTczhz pzhz jzvhi db dkh pvxziAby pz pzhz szjjlba ad dp idezjclba ifzxlvsSdezjclba pz'ss bznzh cvnz vavlbI ubdp, I akzii I hzvsst hzvsst ubdpWzss cztSd ekxc I bzzy jd ivtBzzb sdbzst ilbxz jcz yvtTcz yvt tdk pzbj vpvtSd ivy wkj jhkzFdh ez jczhz'i dbst tdkBzzb xhtlba ilbxz jcz yvtTcz yvt tdk pzbj vpvtTcz yvt tdk pzbj vpvtTcz yvt tdk pzbj vpvtDly I sdiz et sdnz jd idezdbz wzjjzhAby ydzi icz sdnz tdk sluz I ydI yd, tdk ubdp I hzvsst hzvsst ydWzss cztSd ekxc I bzzy jd ivtBzzb sdbzst ilbxz jcz yvtTcz yvt tdk pzbj vpvtSd ivy wkj jhkzFdh ez jczhz'i dbst tdkBzzb xhtlba ilbxz jcz yvtTcz yvt tdk pzbj vpvtWct yd pz bznzh ubdp pcvj pz'nz adj jlss lj'i adbzHdp xdksy I xvhht dbTcz yvt tdk pzbj vpvtCvkiz I'nz wzzb eliilba tdk id ekxc I cvnz jd ivtBzzb xhtlba ilbxz jcz yvtTcz yvt tdk pzbj vpvtTcz yvt tdk pzbj vpvtTcz yvt tdk pzbj vpvt ")中每个英文字母出现的频率,并绘制散点图 极高频率字母:z;次高频率字母:b,d,t,v,;中等频率字母:c,h,I,g,k,p,s,y 低频率字母:a,e,f,l,n,o,u,w,x 超低频率字母:g,m,r,s 由于英文字母在文章中频率不均衡,而单表代替密码将这种不均衡性保留了下来,这就为破译 提供了有力的信息,再结合有关的英文知识,做出以下分析和破译: 从而得到原文: Well I wonder could it be When I was dreaming about you baby You were dreaming of me Call me crazy Call me blind To still be suffering is stupid after all of this time Did I lose my love to someone better And does she love you like I do I do, you know I really really do Well hey So much I need to say Been lonely since the day The day you went away So sad but true For me there's only you Been crying since the day The day you went away I remember date and time September twenty second Sunday twenty five after nine In the doorway with your case No longer shouting at each other There were tears on our faces And we were letting go of something special Something we'll never have again I know, I guess I really really know Well hey So much I need to say Been lonely since the day The day you went away So sad but true For me there's only you Been crying since the day The day you went away The day you went away The day you went away Did I lose my love to someone better And does she love you like I do I do, you know I really really do Well hey So much I need to say Been lonely since the day The day you went away So sad but true For me there's only you Been crying since the day The day you went away Why do we never know what we've got till it's gone How could I carry on The day you went away Cause I've been missing you so much I have to sayBeen crying since the day The day you went away The day you went away The day you went away 实验:通过这次实验，我们很容易就能发现单表代替密码比较简单，只要掌握一定的数 学知识和英语常识就极易被敌方破译，为了增强重要文件的安全性，应采用其他 更安全的设密方式( 大连理工大学 化工学院 化机,,,,班 丁悦 ,,,,,,,,,