全套英文版《计算机网络》ppt电子课件教案_4

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1、Chapter7:NetworksecurityFoundations:whatissecurity?cryptographyauthenticationmessageintegritykeydistributionandcertificationSecurityinpractice:applicationlayer:securee-mailtransportlayer:Internetcommerce,SSL,SETnetworklayer:IPsecurity17:NetworkSecurityFriendsandenemies:Alice,Bob,Trudywell-

2、knowninnetworksecurityworldBob,Alice(lovers!)wanttocommunicate“securely”Trudy,the“intruder”mayintercept,delete,addmessagesFigure7.1goeshere27:NetworkSecurityWhatisnetworksecurity?Secrecy:onlysender,intendedreceivershould“understand”msgcontentssenderencryptsmsgreceiverdecryptsmsgAuthenticat

3、ion:sender,receiverwanttoconfirmidentityofeachotherMessageIntegrity:sender,receiverwanttoensuremessagenotaltered(intransit,orafterwards)withoutdetection37:NetworkSecurityInternetsecuritythreatsPacketsniffing:broadcastmediapromiscuousNICreadsallpacketspassingbycanreadallunencrypteddata(e.g.

4、passwords)e.g.:CsniffsB’spacketsABCsrc:Bdest:Apayload47:NetworkSecurityInternetsecuritythreatsIPSpoofing:cangenerate“raw”IPpacketsdirectlyfromapplication,puttinganyvalueintoIPsourceaddressfieldreceivercan’ttellifsourceisspoofede.g.:CpretendstobeBABCsrc:Bdest:Apayload57:NetworkSecurityInter

5、netsecuritythreatsDenialofservice(DOS):floodofmaliciouslygeneratedpackets“swamp”receiverDistributedDOS(DDOS):multiplecoordinatedsourcesswampreceivere.g.,CandremotehostSYN-attackAABCSYNSYNSYNSYNSYNSYNSYN67:NetworkSecurityThelanguageofcryptographysymmetrickeycrypto:sender,receiverkeysidentic

6、alpublic-keycrypto:encryptkeypublic,decryptkeysecretFigure7.3goeshereplaintextplaintextciphertextKAKB77:NetworkSecuritySymmetrickeycryptographysubstitutioncipher:substitutingonethingforanothermonoalphabeticcipher:substituteoneletterforanotherplaintext:abcdefghijklmnopqrstuvwxyzciphertext:m

7、nbvcxzasdfghjklpoiuytrewqPlaintext:bob.iloveyou.aliceciphertext:nkn.sgktcwky.mgsbcE.g.:Q:Howhardtobreakthissimplecipher?:bruteforce(howhard?)other?87:NetworkSecuritySymmetrickeycrypto:DESDES:DataEncryptionStandardUSencryptionstandard[NIST1993]56-bitsymmetricke