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1、密码学第一章第五题：穷尽法解：有i从0到25进行穷举，可以得到如下可能的明文i=0:BEEAKFYDJXUQYHYJIQRYHTYJIQFBQDUYJIIKFUHCQDi=1:CFFBLGZEKYVRZIZKJRSZIUZKJRGCREVZKJJLGVIDREi=2:DGGCMHAFLZWSAJALKSTAJVALKSHDSFWALKKMHWJESFi=3:EHHDNIBGMAXTBKBMLTUBKWBMLTIETGXBMLLNIXKFTGi=4:FIIEOJCHNBYUCLCNMUVCLXCNMUJFUHYCNMMOJYLGUHi=5
2、:GJJFPKDIOCZVDMDONVWDMYDONVKGVIZDONNPKZMHVIi=6:HKKGQLEJPDAWENEPOWXENZEPOWLHWJAEPOOQLANIWJi=7:ILLHRMFKQEBXFOFQPXYFOAFQPXMIXKBFQPPRMBOJXKi=8:JMMISNGLRFCYGPGRQYZGPBGRQYNJYLCGRQQSNCPKYLi=9:KNNJTOHMSGDZHQHSRZAHQCHSRZOKZMDHSRRTODQLZMi=10:LOOKUPINTHEAIRITSABIRDITSAPLANEITSSUPER
3、MANi=11:MPPLVQJOUIFBJSJUTBCJSEJUTBQMBOFJUTTVQFSNBOi=12:NQQMWRKPVJGCKTKVUCDKTFKVUCRNCPGKVUUWRGTOCPi=13:ORRNXSLQWKHDLULWVDELUGLWVDSODQHLWVVXSHUPDQi=14:PSSOYTMRXLIEMVMXWEFMVHMXWETPERIMXWWYTIVQERi=15:QTTPZUNSYMJFNWNYXFGNWINYXFUQFSJNYXXZUJWRFSi=16:RUUQAVOTZNKGOXOZYGHOXJOZYGVR
4、GTKOZYYAVKXSGTi=17:SVVRBWPUAOLHPYPAZHIPYKPAZHWSHULPAZZBWLYTHUi=18:TWWSCXQVBPMIQZQBAIJQZLQBAIXTIVMQBAACXMZUIVi=19:UXXTDYRWCQNJRARCBJKRAMRCBJYUJWNRCBBDYNAVJWi=20:VYYUEZSXDROKSBSDCKLSBNSDCKZVKXOSDCCEZOBWKXi=21:WZZVFATYESPLTCTEDLMTCOTEDLAWLYPTEDDFAPCXLYi=22:XAAWGBUZFTQMUDUFE
5、MNUDPUFEMBXMZQUFEEGBQDYMZi=23:YBBXHCVAGURNVEVGFNOVEQVGFNCYNARVGFFHCREZNAi=24:ZCCYIDWBHVSOWFWHGOPWFRWHGODZOBSWHGGIDSFAOBi=25:ADDZJEXCIWTPXGXIHPQXGSXIHPEAPCTXIHHJETGBPC经过尝试，可以得到当Ii=10的时候为明文正解，即为lookintheair,it’sabird,it’splane,it’ssuperman.第21题：第一小题：首先算出每一个字母出现的频率，如下（包括字母出
6、现的次数，以及频率）：A:5,0.019608B:0,0.000000C:37,0.145098D:8,0.031373E:12,0.047059F:9,0.035294G:23,0.090196H:5,0.019608I:15,0.058824J:7,0.027451K:18,0.070588L:7,0.027451M:5,0.019608N:13,0.050980O:10,0.039216P:6,0.023529Q:1,0.003922R:0,0.000000S:20,0.078431T:0,0.000000U:14,0.05490
7、2V:0,0.000000W:5,0.019608X:7,0.027451Y:15,0.058824Z:13,0.050980可以统计出频率最大的10个字母是:C(0.145098);G(0.090196);K(0.070588);S(0.078431);E(0.047059);I(0.058824);N(0.050980);U(0.054902);Y(0.058824);Z(0.050980).可以确定C->E;ABCDEFGHIJKLMV#EBIWAFDCSYMNOPQRSTUVWXYZLNUJ#O#T#GPRH发现明文段FZCCN
8、,即是W*EE*，通过词典可以猜测为wheel，即是Z->h,N->l；而h,l的频率也满足常规出现的概率，有理由相信是对的。有高频CG(7);ZC(7);AC(5);CK(5);CN(5);NC(5);C
