密码破译问题中的Mathmatic.doc

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分析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: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 jczhzi 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 pzss 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 jczhzi 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 jczhzi dbst tdkBzzb xhtlba ilbxz jcz yvtTcz yvt tdk pzbj vpvtWct yd pz bznzh ubdp pcvj pznz adj jlss lji adbzHdp xdksy I xvhht dbTcz yvt tdk pzbj vpvtCvkiz Inz 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 beWhen I was dreaming about you babyYou were dreaming of meCall me crazyCall me blindTo still be suffering is stupid after all of this timeDid I lose my love to someone betterAnd does she love you like I doI do, you know I really really doWell heySo much I need to sayBeen lonely since the dayThe day you went awaySo sad but trueFor me theres only youBeen crying since the dayThe day you went awayI remember date and timeSeptember twenty secondSunday twenty five after nineIn the doorway with your caseNo longer shouting at each otherThere were tears on our facesAnd we were letting go of something specialSomething well never have againI know, I guess I really really knowWell heySo much I need to sayBeen lonely since the dayThe day you went awaySo sad but trueFor me theres only youBeen crying since the dayThe day you went awayThe day you went awayThe day you went awayDid I lose my love to someone betterAnd does she love you like I doI do, you know I really really doWell heySo much I need to sayBeen lonely since the dayThe day you went awaySo sad but trueFor me theres only youBeen crying since the dayThe day you went awayWhy do we never know what weve got till its goneHow could I carry onThe day you went awayCause Ive been missing you so much I have to sayBeen