分组密码的工作模式

《分组密码的工作模式》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

1、第6章分组密码的工作模式MultipleEncryption&3DESclearareplacementforDESwasneededtheoreticalattacksthatcanbreakitdemonstratedexhaustivekeysearchattacksAESisanewcipheralternativepriortothisalternativewastousemultipleencryptionwithDESimplementationsTripleDES(3DES)isthechosenformWhynotDouble-DE

2、S?coulduse2DESencryptsoneachblockC=E(K2,E(K1,P))P=D(K1,D(K2,C))issueofreductiontosinglestage(约化为单次加密),andhave“meet-in-the-middle”attackworkswheneveruseaciphertwicesinceX=E(K1,P)=D(K2,C),attackbyencryptingPwithallkeysandstore,thendecryptCwithkeysandmatchXvaluecanshowtakesO(256)s

3、tepsRequireknow…Triple-DESwithTwo-Keyshencemustuse3encryptionswouldseemtoneed3distinctkeysbutcanuse2keyswithE-D-EsequenceC=EK1(DK2(EK1(P)))nbencrypt&decryptequivalentinsecurityifK1=K2thencanworkwithsingleDESstandardizedinANSIX9.17&ISO8732nocurrentknownpracticalattacksO(2112)穷举攻

4、击/1052差分密码分析Triple-DESwithThree-Keysalthougharenopracticalattacksontwo-keyTriple-DEShavesomeindicationscanuseTriple-DESwithThree-KeystoavoideventheseC=EK3(DK2(EK1(P)))hasbeenadoptedbysomeInternetapplications,egPGP,S/MIMEModesofOperationblockciphersencryptfixedsizeblockseg.DESen

5、crypts64-bitblockswith56-bitkeyneedsomewaytoen/decryptarbitraryamountsofdatainpractiseNIST(SP800-38A)ModesofUsedefines5possiblemodesdefinedforAES&DEShaveblockandstreammodestocoverawidevarietyofapplicationscanbeusedwithanyblockcipherElectronicCodebookBook(ECB)messageisbrokeninto

6、independentblockswhichareencryptedeachblockisavaluewhichissubstituted,likeacodebook,hencenameeachblockisencodedindependentlyoftheotherblocksCi=DESK1(Pi)uses:securetransmissionofsinglevaluesElectronicCodebookBook(ECB)AdvantagesandLimitationsofECBmessagerepetitionsmayshowincipher

7、textifalignedwithmessageblockparticularlywithdatasuchgraphicsorwithmessagesthatchangeverylittle,whichbecomeacode-bookanalysisproblemweaknessisduetotheencryptedmessageblocksbeingindependentmainuseissendingafewblocksofdataCipherBlockChaining(CBC)messageisbrokenintoblockslinkedtog

8、etherinencryptionoperationeachpreviouscipherblocksisch