第12章 Hash和MAC算法

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1、第12章消息认证码MessageAuthenticationmessageauthenticationisconcernedwithprotectingtheintegrityofamessagevalidatingidentityoforiginatornon-repudiationoforigin(disputeresolution)willconsiderthesecurityrequirementsthenthreealternativefunctionsusedmessageencryptionhashfunct

2、ionmessageauthenticationcode(MAC)SecurityRequirementsdisclosuretrafficanalysismasqueradecontentmodificationsequencemodificationtimingmodificationsourcerepudiationdestinationrepudiationSymmetricMessageEncryptionencryptioncanalsoprovidesauthenticationifsymmetricencr

3、yptionisusedthen:receiverknowsendermusthavecreatedit,sinceonlysenderandreceiverknowkeyusedknowcontentcannothavebeenaltered,ifmessagehassuitablestructure,redundancyorachecksumtodetectanychangesPublic-KeyMessageEncryptionifpublic-keyencryptionisused:encryptionprovid

4、esnoconfidenceofsendersinceanyonepotentiallyknowspublic-keyhoweverifsendersignsmessageusingtheirprivate-keythenencryptswithrecipientspublickeyhavebothsecrecyandauthenticationagainneedtorecognizecorruptedmessagesbutatcostoftwopublic-keyusesonmessageHashandMACAlgori

5、thmsHashFunctionscondensearbitrarysizemessagetofixedsizebyprocessingmessageinblocksthroughsomecompressionfunctioneithercustomorblockcipherbasedMessageAuthenticationCode(MAC)fixedsizedauthenticatorforsomemessagetoprovideauthenticationformessagebyusingblockciphermod

6、eorhashfunctionMessageAuthenticationCode(MAC)generatedbyanalgorithmthatcreatesasmallfixed-sizedblockdependingonbothmessageandsomekeylikeencryptionthoughneednotbereversibleappendedtomessageasasignaturereceiverperformssamecomputationonmessageandchecksitmatchestheMAC

7、providesassurancethatmessageisunalteredandcomesfromsenderMessageAuthenticationCodeasmallfixed-sizedblockofdatageneratedfrommessage+secretkeyMAC=C(K,M)appendedtomessagewhensentMessageAuthenticationCodesasshowntheMACprovidesauthenticationcanalsouseencryptionforsecre

8、cygenerallyuseseparatekeysforeachcancomputeMACeitherbeforeorafterencryptionisgenerallyregardedasbetterdonebeforewhyuseaMAC?sometimesonlyauthenticationis