四讲古典置换密码classicaltranspositionciphers.ppt

第四讲古典置换密码(classicaltranspositionciphers)上海交通大学计算机科学系郑东zheng-******@:62932135(O)变换密码transpositionciphers本节考虑变换密码(或置换密码)方法:通过重新编排消息字母隐藏信息特点:,密钥是纸条和圆柱的宽度以不同的行写下消息字母按行读取消息Plain:URDCMIAIOQEECipher:,,按另一规则读出密文。密钥:-Rowtranspositionciphersgroupthemessageandshuffleletterswithineachgroupmoreformallywritelettersacrossrowsthenreorderthecolumnsbeforereadingofftherowsalwayshaveanequivalentpairofkeys(ReadoffvsWriteIn)(续1)Plain:THESIMPLESTPOSSIBLETRANSPOSITIONSXXKey(R):25413Key(W):              41532        THESISTIEH        MPLESEMSLP        TPOSSSTSOP        IBLETEITLB        RANSPSRPNA        OSITITOIIS       ONSXXXOXSNCipher:(续2)可以用一个英文单词做密钥,指定以字母顺序做为读取密文(或明文)Plain:CONVENIENTWAYTOEXPRESSTHEPERMUTATIONKey(W):COMPUTERKey(W):14358726ANOVINCEEWTAOTNYERPETSXSHEPRTUEMAOINZZTZCipher::Key(R):sorcery=>6341257laserbeamscanbemodulatedtocarrymoreintelligencethanradiowaves==>erasblecamsnabdumoleatoedctamoryrreelntliiceentghadnriaoesavw