现代密码学02---附件2-频率分析

频率分析林喜军中国海洋大学信息安全实验室第2章《古典密码学》附件22•考虑下面的密文：YIFQFMZRWQFYVECFMDZPCVMRZWNMDZVEJBTXCDDUMJNDIFEFMDZCDMQZKCEYFCJMYRNCWJCSZREXCHZUNMXZNZUCDRJXYYSMRTMEYIFZWDYVZVYFZUMRZCRWNZDZJJXZWGCHSMRNMDHNCMFQCHZJMXJZWIEJYUCFWDJNZDIR3统计密文中各字母的出现次数•Z出现的次数远高于其他字母，所以猜测Ze•出现次数超过10的字母有{C、D、F、J、M、R、Y}，它们可能对应{t、a、o、i、n、s、h、r}，但不能确定是哪一个4考虑形如-e和e-的双字母组合eW出现4次，We一次也没出现W出现的频率为0.048，故猜测WdYIFQFMeRWQFYVECFMDePCVMReWNMDeVEJBTXCDDUMJNDIFEFMDeCDMQeKCEYFCJMYRNCWJCSeREXCHeUNMXeNeUCDRJXYYSMRTMEYIFeWDYVeVYFeUMReCRWNeDeJJXeWGCHSMRNMDHNCMFQCHeJMXJeWIEJYUCFWDJNeDIRYIFQFMeRdQFYVECFMDePCVMRedNMDeVEJBTXCDDUMJNDIFEFMDeCDMQeKCEYFCJMYRNCdJCSeREXCHeUNMXeNeUCDRJXYYSMRTMEYIFedDYVeVYFeUMReCRdNeDeJJXedGCHSMRNMDHNCMFQCHeJMXJedIEJYUCFdDJNeDIR•在Wd的猜测下：•R在密文中频繁出现，Rd出现2次。•n是英文中出现频率较高的字母，nd是英文中常见的字母组合，可以猜测RnYIFQFMendQFYVECFMDePCVMnedNMDeVEJBTXCDDUMJNDIFEFMDeCDMQeKCEYFCJMYnNCdJCSenEXCHeUNMXeNeUCDnJXYYSMnTMEYIFedDYVeVYFeUMneCndNeDeJJXedGCHSMnNMDHNCMFQCHeJMXJedIEJYUCFdDJNeDIn6•Ne是出现较多的字母组合，eN没出现，所以猜测Nh•如果猜测正确，根据明文片段neCndNe，又可以猜测Ca(可能为neandhe形式的明文)YIFQFMendQFYVEaFMDePaVMnedhMDeVEJBTXaDDUMJhDIFEFMDeaDMQeKaEYFaJMYnhadJaSenEXaHeUhMXeheUaDnJXYYSMnTMEYIFedDYVeVYFeUMneandheDeJJXedGaHSMnhMDHhaMFQaHeJMXJedIEJYUaFdDJheDIn•考虑出现次数都很高的De和eD，故猜测D{r,s,t}YIFQFMendQFYVEaFMDePaVMnedhMDeVEJBTXaDDUMJhDIFEFMDeaDMQeKaEYFaJMYnhadJaSenEXaHeUhMXeheUaDnJXYYSMnTMEYIFedDYVeVYFeUMneandheDeJJXedGaHSMnhMDHhaMFQaHeJMXJedIEJYUaFdDJheDIn•考虑频率排第二的M•片段nhM，这说明h可能是某单词的首字母，M可能代表元音•所以猜测M{i,o}•密文中出现aM，因为ai比ao更常出现，所以猜测MiD{r,s,t}•o是常见的明文字母，可以猜测对应的密文中常出现的字母{D,F,J,Y}中的某一个。•密文出现aFi、aJi，如果o对应F或J，明文中将出现aoi的元音组合，不太可能。•猜测YoD{r,s,t}YIFQFiendQFYVEaFiDePaVinedhiDeVEJBTXaDDUiJhDIFEFiDeaDiQeKaEYFaJiYnhadJaSenEXaHeUhiXeheUaDnJXYYSinTiEYIFedDYVeVYFeUineandheDeJJXedGaHSinhiDHhaiFQaHeJiXJedIEJYUaFdDJheDIn•再考虑可能有{D、F、J}{r,s,t}•密文中hiD出现2次，故猜测Ds•这样，hiDhis•这与前面假设D{r,s,t}是一致的D{r,s,t}oIFQFiendQFoVEaFiDePaVinedhiDeVEJBTXaDDUiJhDIFEFiDeaDiQeKaEoFaJionhadJaSenEXaHeUhiXeheUaDnJXooSinTiEoIFedDoVeVoFeUineandheDeJJXedGaHSinhiDHhaiFQaHeJiXJedIEJoUaFdDJheDIn•考虑字母组合HhaiF•可猜测它对应的明文可能是chair。由此猜测Hc，Fr•这样，JtoIFQFiendQFoVEaFisePaVinedhiseVEJBTXassUiJhsIFEFiseasiQeKaEoFaJionhadJaSenEXaHeUhiXeheUasnJXooSinTiEoIFedsoVeVoFeUineandheseJJXedGaHSinhisHhaiFQaHeJiXJedIEJoUaFdsJhesIn{F,J}{r,t}猜测QfoIrQriendQroVEarisePaVinedhiseVEtBTXassUithsIrEriseasiQeKaEorationhadtaSenEXaceUhiXeheUasntXooSinTiEoIredsoVeVoreUineandhesettXedGacSinhischairQacetiXtedIEtoUardsthesIn猜测Iu,VmoIrfriendfroVEarisePaVinedhiseVEtBTXassUithsIrEriseasifeKaEorationhadtaSenEXaceUhiXeheUasntXooSinTiEoIredsoVeVoreUineandhesettXedGacSinhischairfacetiXtedIEtoUardsthesIn猜测EpourfriendfromEarisePaminedhisemEtBTXassUithsurEriseasifeKaEorationhadtaSenEXaceUhiXeheUasntXooSinTiEouredsomemoreUineandhesettXedGacSinhischairfacetiXteduEtoUardsthesun猜测Px，ByourfriendfromparisePaminedhisemptBTXassUithsurpriseasifeKaporationhadtaSenpXaceUhiXeheUasntXooSinTipouredsomemoreUineandhesettXedGacSinhischairfacetiXteduptoUardsthesun猜测XlourfriendfromparisexaminedhisemptyTXassUithsurpriseasifeKaporationhadtaSenpXaceUhiXeheUasntXooSinTipouredsomemoreUineandhesettXedGacSinhischairfacetiXteduptoUardsthesun猜测TgourfriendfromparisexaminedhisemptyTlassUithsurpriseasifeKaporationhadtaSenplaceUhileheUasntlooSinTipouredsomemoreUineandhesettledGacSinhischairfacetilteduptoUardsthesun猜测Uw，Kv，SkourfriendfromparisexaminedhisemptyglassUithsurpriseasifeKaporationhadtaSenplaceUhileheUasntlooSingipouredsomemoreUineandhesettledGacSinhischairfacetilteduptoUardsthesun猜测GbourfriendfromparisexaminedhisemptyglasswithsurpriseasifevaporationhadtakenplacewhilehewasntlookingipouredsomemorewineandhesettledGackinhischairfacetilteduptowardsthesun20最后，恢复完整的明文如下：OurfriendfromParisexaminedhisemptyglasswithsurprise,asifevaporationhadtakenplacewhilehewasn’tlooking.Ipouredsomemorewineandhesettledbackinhischair,facetilteduptowardsthesun.