资讯安全72课件

資訊安全

NetworkSecurityInstructor:孫宏民hmsun@.tw

Room:EECS6402,Tel:03-5742968,Fax:886-3-572-36941Textbook:

C.Kaufman,R.Perlman,andM.Speciner,NetworkSecurity,SecondEdition,Prentice-HallPTR,2002.

ReferenceBooks:

1.W.Ford,ComputerCommunicationsSecurity:principles,StandardProtocols,andTechniques,PrenticeHall,1994.2.W.Stallings,NetworkSecurityEssentials,SecondEdition,PrenticeHall,2003.

GradingScheme:

Project50%,Paper25%,Exams25%

2Chapter2IntroductiontoCryptographyInstructor:孫宏民3Cipher(Cryptosystem):

secretmethodofwritingCiphertexts:

AnencryptedmessagesSenderReceiverIntruderModelofConventionalCryptosystem5Cryptographyisthestudyofcreatingandusingsecretwriting,ortheartandscienceofkeepingmessagessecure.Encryption(Enciphering):Theencryptionistheprocessofdisguisingamessageinsuchawayastohideitssubstance.Notation:C=E(M)orEK(M)orEK1(M)Decryption(Deciphering):Theprocessofturningciphertextbackintoplaintext.Notation:M=D(C)orDK(C)orDK2(C)6Cryptanalysis:

Theartandscienceofbreakingciphertexts.Cryptographersv.s.CryptanalystsCryptology=Cryptography+Cryptanalysis7FourBasicServicesofCryptographyIntegrity:

Itshouldbepossibleforthereceiverofamessagetoverifythatithasnotbeenmodifiedintransit;anintrudercannotsubstituteafalsemessageforalegitimateone.Nonrepudiation:

Asendershouldnotbeabletofalselydenylaterthathesentamessage.92.2BreakinganEncryptionScheme(1)Acipherisbreakableifitispossibletofindplaintextorkeyfromciphertext,ortofindthekeyfromplaintext-ciphertextpairs.Cryptanalysis=study(methods)ofbreakingsystem,thatis,decipheringwithoutthekey(K2),using:102.2BreakinganEncryptionScheme(2)(a)Ciphertextonly(C)Mostdifficulttobreak(b)Knownplaintext(M,C)E.g.,encryptedprograms(while,if,else,...)(c)Chosenplaintext(M*,C)GetthesendertoencipherM*(yourchoice)foryou.(d)Chosenciphertext(M,C*)GetthereceivertodecipherC*(yourchoice)foryou.11SomeothertypesofCryptanalyticAttacks(1)Adaptive-chosen-plaintextAttacks(aspecialcaseofachosen-plaintextattack):

Theintrudernotonlycanchoosetheplaintextthatisencrypted,buthecanalsomodifyhischoicebasedontheresultsofpreviousencryption.Chosen-keyAttacks:

Theintrduerhassomeknowledgeabouttherelationshipbetweendifferentkeys.13SomeothertypesofCryptanalyticAttacks(2)Bruce-forceAttacks(Exhaustivesearch):

Totryeverypossiblekeyonebyoneandtocheckwhethertheresultingplaintextismeaningful.142.3TypeofCryptographicFunctionHashFunctionSecretKeyFunctionPublicKeyFunction

15plaintextencryptionciphertextkeyciphertextplaintextdecryption17ExampleofaCiphermi,ci

{00,01,02,...,25}Toencipher:M=m1m2m3…C=c1c2c3…18Todecipher:19CodeBookPlaintextwordsorphrasesareenteredintothecodebooktogetherwiththeirciphertextsubstitutes.Thecodebookisthekey.Example:ATTACKJAPAN40085603WordCodeBOMB1701JAPAN5603ATTACK4008NIGHT3790

212.5PublicKeyCryptosystemsPublicKeyCryptosystems:

Encryption&decryptionkeysaredifferent(EK1(M)=C&DK2(C)=M),suchasRSA,ElGamal,andMcEliece.Theencryptionkey(publickey)canbepublicwhilethedecryptionkey(secretkey)cannotbecalculatedfromthepublickey.22Encryptionanddecryptionaretwomathmaticalfunctionsthatincersesofeachother.plaintextencryptionciphertextPrivatekeyciphertextplaintextdecryptionPublickey232.6HashAlgorithmAcryptographichashfunctionisamathematicaltransformationthattakesamessageofarbitrarylengthandcomputesfromitafixed-lengthnumber.Wewillcallthehashofamessagem,h(m).25Ithasthefollowingproperty:Foranymessage,itiseasytocomputeh(m).Givenh(m),thereisnowaytofindamthathashestoh(m)inawaythatissubstantiallyeasierthangoingthroughallpossiblevaluesofmandcomputingh(m)foreachone.Itiscomputationallyinfeasibletofindtwovaluethathashtothesamething.26InterruptionThisisanattackonavailability.Examples:cuttingofacommunicationline,ordestructionofapieceofhardware.InterceptionThisisanattackonsecrecy.Examples:wiretappingtocapturedatainnetwork,orillicitcopyingoffilesorprograms.29ModificationThisisanattackonintegrity.Examples:changingvaluesinadatafile,oralteringaprogramsothatitperformsdifferently.FabricationThisisanattackonauthenticity.Examples:insertionoffakemessagesinnetwork,oradditionofrecordstoafile.30SecurityThreatsPassivethreatsInterception(Secrecy)ActivethreatsInterruption(Availability)Modification(Integrity)Fabrication(Authenticity)31DataSecurity(1)Datasecurityisthescienceandstudyofmethodsofprotectingdataincomputerandcommunicationssystems.Datasecuritystudiesfourkindsofcontrol:CryptographyAccessInformationflowPreventleakageInferencePeopleshouldn'tbeabletoinfersomethingthatshouldn'tbeinferred32DataSecurity(2)ThreatstodataincomputersystemsSecrecyBrowsing,Leakage,InferenceAuthenticityTampering,AccidentaldestructionBrowsingSearchingthroughmainmemoryorsecondarystorage33DataSecurity(3)Leakage

Transmissionofdatatounauthorizedusersbyprocesseswithlegitimateaccesstothedata(e.g.,compilers,texteditors,...)Inference

Inastatisticaldatabase,youmayinfertheinfoofanindividualfromaverage.

34DataSecurity(4)TamperingReplayinsertDeleteAccidentaldestructionUnintentionaloverwritingCausedbyfaultysoftware(e.g.,anarraysubscriptisout-of-range)Accesscontrolsareneededtopreventprogramsfromwritingintomemoryregionsofotherprograms35DataSecurity(5)UnintentionaldeletionCausedbysoftwareorhardwarefailureorusermistakes(e.g.,adiskcrash)Backupisneededtorecoverfromdestruction36OtherThreatstoDataSecurityCiphertextsearching

xyz xyz salary(example)

Youdon'tknowwhatxyzis,butknowtheyarethesame.KnowoneofthemKnowbothMasquerading

Writeprogramstosimulateloginproceduretogetotherpeople'spassword.

37ComputerSystem38CryptographicSystemForagivenK,DKistheinverseofEK;thatis,DK(EK(M))=MRequirementsforcryptosystems:K,EKandDKareefficient(runinpolynomialtime)Systemiseasytouse(no200digitskeyshastobetyped)SecuritydependsonlyonthesecrecyofK,notonEorD39-A2D5G8KbNfQiTlXo#r%v(y0B3E6I9LcOgRjVmYp!t&w)z1C4G7JaMePhSkWnZr$u*x+A2D5H8KbNfQiUlXo#s%v(y0B3F6I9LdOgRjVmYq!t&w-z1C4G7JbMePhTkWnZr$u(x+A2E5H8KcNfRiUlXp#s%v)y0C3F6IaLdOgSjVmYq!t*w-z1D4G7JbMeQhTkWoZr$u(x+B2E5H9KcNfRiUmXp#s&v)y0C3F7IaLdPgSjVnYq$t*w-A1D4G8JbNeQhTlWoZr%u(y+B2E6H9KcOfRiUmXp!s&v)z0C3F7IaMdPgSkVnYq$t*x-A1D5G8JbNeQiTlWo#r%u(y+B3E6H9LcOfRjUmYp!s&w)z0C4F7JaMdPhSkVnZq$t*x-A2D5G8KbNeQiTlXo#r%v(y+B3E6I9LcOgRjUmYp!t&w)z1C4F7JaMePhSkWnZq$u*x+A2D5H8KbNfQiUlXo#s%v(y0B3E6I9LdOgRjVmYp!t&w-z1C4G7JaMePhTkWnZr$u*x+A2E5H8KcNfQiUlXp#s%v)y0B3F6IaLdOgSjVmYq!t*w-z1D4G7JbMeQhTkWoZr$u(x+A2E5H9KcNfRiUlXp#s&v)y0C3F6IaLdPgSjVnYq!t*w-A1D4G8JbMeQhTlWoZr%u(x+B2E6H9KcOfRiUmXp!s&v)z0C3F7IaLdPgSkVnYq$t*w-A1D5G8JbNeQhTlWo#r%u(y+B2E6H9LcOfRjUmXp!s&w)z0C4F7IaMdPhSkVnZq$t*x-A2D5G8KbNeQiTlWo#r%v(y+B3E6H9LcOgRjUmYp!s&w)z1C4F7JaMdPhSkWnZq$u*x-A2D5H8KbNfQiTlXo#s%v(y0B3E6I9LdOgRjVmYp!t&w-z1C4G7JaMePhSkWnZr$u*x+A2D5H8KcNfQiU!s&w)z1C4F7JaMdPhSkWnZq$u*x-A2D5H8KbNfQiTlXo#s%v(y0B3E6I9LcOgRjVmYp!t&w)z1C4G7JaMePhSkWnZr$u*x+A2D5H8KcNfQiUlXo#s%v)y0B3F6I9LdOgSjVmYq!t&w-z1D4G7JbMePhTkWoZr$u(x+A2E5H8KcNfRiUlXp#s%v)y0C3F6IaLdOgSjVnYq!t*w-z1D4G8JbMeQhTkWoZr%u(x+B2E5H9KcOfRiUmXp#s&v)z0C3F7IaLdPgSjVnYq$t*w-A1D4G8JbNeQhTlWoZr%u(y+B2E6H9KcOfRjUmXp!s&v)z0C4F7IaMdPgSkVnZq$t*x-A1D5G8KbNeQiTlWo#r%v(y+B3E6H9LcOfRjUmYp!s&w)z0C4F7JaMdPhSkVnZq$u*x-A2D5G8KbNfQiTlXo#r%v(y0B3E6I9LcOgRjVmYp!t&w)z1C4G7JaMePhSkWnZq$u*x+A2D5H8KbNfQiUlXo#s%v(y0B3F6I9LdOgRjVmYq!t&w-z1C4G7JbMePhTkWnZr$u(x+A2E5H8KcNfRiUlXp#s%v)y0B3F6IaLdOgSjVmYq!t*w-z5H8KbNfQiUlXo#s%v(y0B3F6I9LdOgRjVmYq!t&w-z1C4G7JbMePhTkWnZr$u(x+A2E5H8KcNfQiUlXp#s%v)y0B3F6IaLdOgSjVmYq!t*w-z1D4G7JbMeQhTkWoZr$u(x+B2E5H9KcNfRiUmXp#s&v)y0C3F7IaLdPgSjVnYq!t*w-A1D4G8JbMeQhTlWoZr%u(x+B2E6H9KcOfRiUmXp!s&v)z0C3F7IaMdPgSkVnYq$t*x-A1D5G8JbNeQiTlWo#r%u(y+B3E6H9LcOfRjUmXp!s&w)z0C4F7IaMdPhSkVnZq$t*x-A2D5G8KbNeQiTlXo#r%v(y+B3E6I9LcOgRjUmYp!t&w)z1C4F7JaMePhSkWnZq$u*x-A2D5H8KbNfQiTlXo#s%v(y0B3E6I9LdOgRjVmYp!t&w-z1C4G7JaMePhTkWnZr$u*x+A2E5H8KcNfQiUlXp#s%v)y0B3F6I9LdOgSjVmYq!t&w-z1D4G7JbMePhTkWoZr$u(x+A2E5H9KcNfRiUlXp#s&v)y0C3F6IaLdPgSjVnYq!t*w-A1D4G8JbMeQhTlWoZr%u(x+B2E5H9KcOfRiUmXp#s&v)z0C3F7IaLdPgSkVnu(x+A2E5H9KcNfRiUlXp#s&v)y0C3F6IaLdPgSjVnYq!t*w-z1D4G8JbMeQhTkWoZr%u(x+B2E5H9KcOfRiUmXp#s&v)z0C3F7IaLdPgSkVnYq$t*w-A1D5G8JbNeQhTlWo#r%u(y+B2E6H9LcOfRjUmXp!s&v)z0C4F7IaMdPgSkVnZq$t*x-A1D5G8KbNeQiTlWo#r%v(y+B3E6H9LcOgRjUmYp!s&w)z1C4F7JaMdPhSkWnZq$u*x-A2D5G8KbNfQiTlXo#r%v(y0B3E6I9LcOgRjVmYp!t&w)z1C4G7JaMePhSkWnZr$u*x+A2D5H8KcNfQiUlXo#s%v)y0B3F6I9LdOgRjVmYq!t&w-z1C4G7JbMePhTkWnZr$u(x+A2E5H8KcNfRiUlXp#s%v)y0C3F6IaLdOgSjVnYq!t*w-z1D4G8JbMeQhTkWoZr%u(x+B2E5H9KcNfRiUmXp#s&v)y0C3F7IaLdPgWnZr$u(x+A2E5H8KcNfRiUlXp#s%v)y0C3F6IaLdOgSjVnYq!t*w-z1D4G7JbMeQhTkWoZr$u(x+B2E5H9KcNfRiUmXp#s&v)y0C3F7IaLdPgSjVnYq$t*w-A1D4G8JbNeQhTlWoZr%u(y+B2E6H9KcOfRjUmXp!s&v)z0C3F7IaMdPgSkVnYq$t*x-A1D5G8JbNeQiTlWo#r%u(y+B3E6H9LcOfRjUmYp!s&w)z0C4F7JaMdPhSkVnZq$u*x-A2D5G8KbNeQiTlXo#r%v(y+B3E6I9LcOgRjUmYp!t&w)z1C4F7JaMePhSkWnZq$u*x+A2D5H8KbNfQiUlXo#s%v(y0B3F6IPhSkVnZq$t*x-A2D5G8KbNeQiTlXo#r%v(y+B3E6I9LcOgRjUmYp!t&w)z1C4F7JaMePhSkWnZq$u*x+A2D5H8KbNfQiUlXo#s%v(y0B3E6I9LdOgRjVmYp!t&w-z1C4G7JaMePhTkWnZr$u*x+A2E5H8KcNfQiUlXp#s%v)y0B3F6IaLdOgSjVmYq!t*w-z1D4G7JbMePhTkWoZr$u(x+A2E5H9KcNfRiUlXp#s&v)y0C3F6IaLdPgSjVnYq!t*w-A1D4G8JbMeQhTlWoZr%u(x+B2E6H9KcOfRiUmXp!s&v)z0C3F7IaLhTkWoZr$u(x+A2E5H9KcNfRiUlXp#s&v)y0C3F6IaLdPgSjVnYq!t*w-A1D4G8JbMeQhTlWoZr%u(x+B2E5H9KcOfRiUmXp#s&v)z0C3F7IaLdPgSkVnYq$t*w-A1D5G8JbNeQhTlWo#r%u(y+B2E6H9LcOfRjUmXp!s&w)z0C4F7IaMdPhSkVnZq$t*x-A1D5G8KbNeQiTlWo#r%v(y+B3E6H9LcOgRjUmYp!s&w)z1C4F7JaMdPhSkWnZq$u*x-A2D5H8KbNfQiTlXo#s%v(y0B3E6I9LcOgRjVmYp!t&w)z1C4G7JaMePhSkWnZr$u*x+A2D5H8KcNfQiUlXo#s%v)y0B3F6I9LdOgSjVmYq!t&w-z1D4G7JbMePhTkWnZr$u(x+A2E5H8KcNfRiUlXp#s%v)y0C3F6IaLdSkWnZr$u*x+A2D5H8KcNfQiUlXo#s%v)y0B3F6I9LdOgSjVmYq!t&w-z1C4G7JbMePhTkWnZr$u(x+A2E5H8KcNfRiUlXp#s%v)y0C3F6IaLdOgSjVnYq!t*w-z1D4G8JbMeQhTkWoZr%u(