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AnIntroduc+ontoAppliedCryptography

ChesterRebeiroIITMadras

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ConnectedandStoredEverythingisconnected!

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Everythingisstored!

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IncreasedSecurityBreaches

81%morein2015

h9p://www.pwc.co.uk/assets/pdf/2015-isbs-execuGve-summary-02.pdf

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SecurityThreats(whydifficulttoprevent?)

A9ackersneedtotargettheweakestlinkinthechain

Networks/CommunicaGonlinks

Hardware

Peripherals

SystemSoPware(OperaGngSystems/Hypervisor)

ApplicaGons

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SecurityStudies(Research)Networks/CommunicaGonlinks

Hardware

Peripherals

SystemSoPware(OperaGngSystems/Hypervisor)

ApplicaGons

NetworkSecurity

HardwareSecurity

SystemSecurity

OSSecurity

CloudSecurityWebSecurity

DBMSSecurity

EmbeddedSecurity

Cryptography

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Cryptography

•  Acrucialcomponentinallsecuritysystems•  Fundamentalcomponenttoachieve

– Confiden+ality

Allowsonlyauthorizedusersaccesstodata

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Cryptography(itsuse)

•  Acrucialcomponentinallsecuritysystems•  Fundamentalcomponenttoachieve

– ConfidenGality– DataIntegrity

CryptographycanbeusedtoensurethatonlyauthorizeduserscanmakemodificaGons(forinstancetoabankaccountnumber)

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Cryptography(itsuse)

•  Acrucialcomponentinallsecuritysystems•  Fundamentalcomponenttoachieve

– ConfidenGality– DataIntegrity– Authen+ca+on

CryptographyhelpsproveidenGGes

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Cryptography(itsuse)

•  Acrucialcomponentinallsecuritysystems•  Fundamentalcomponenttoachieve

– ConfidenGality– DataIntegrity– AuthenGcaGon– Non-repudia+on

Thesenderofamessagecannotclaimthatshedidnotsendit

Ididnotsendthat

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SchemeforConfiden+ality

Alice Bob

messageA9ackatDawn!!

untrustedcommunicaGonlink

MalloryProblem:AlicewantstosendamessagetoBob(andonlytoBob)throughanuntrustedcommunicaGonlink

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Encryp+on

Alice Bob

message“A9ackatDawn!!”

untrustedcommunicaGonlink

MallorySecrets• OnlyAliceknowstheencrypGonkeyKE• OnlyBobknowsthedecrypGonkeyKD

E D

KE KD

“A9ackatDawn!!”encrypGon decrypGon

#%AR3Xf34^$(ciphertext)

Onlyseesciphertext.cannotgettheplaintextmessagebecauseshedoesnotknowthekeys

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Encryp+onAlgorithms

Alice BobuntrustedcommunicaGonlinkE D

KE KD

“A9ackatDawn!!”encrypGon decrypGon

#%AR3Xf34($(ciphertext)

•  ShouldbeeasytocomputeforAlice/Bob(whoknowthekey)•  ShouldbedifficulttocomputeforMallory(whodoesnotknowthekey)•  Whatis‘difficult’?

•  Idealcase:ProvethattheprobabilityofMallorydeterminingtheencrypGon/decrypGonkeyisnobe&erthanarandomguess

•  Computa+onally:ShowthatitisdifficultforMallorytodeterminethekeysevenifshehasmassivecomputaGonalpower

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Ciphers•  SymmetricAlgorithms

–  EncrypGonandDecrypGonusethesamekey–  i.e.KE=KD–  Examples:

•  BlockCiphers:DES,AES,PRESENT,etc.•  StreamCiphers:A5,Grain,etc.

•  AsymmetricAlgorithms–  EncrypGonandDecrypGonkeysaredifferent–  KE≠KD–  Examples:

•  RSA•  ECC

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Encryp+onKeys

•  Howarekeysmanaged– HowdoesAlice&Bobselectthekeys?– Needalgorithmsforkeyexchange

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Alice BobuntrustedcommunicaGonlinkE D

KE KD

“A9ackatDawn!!”encrypGon decrypGon

#%AR3Xf34($(ciphertext)

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AlgorithmicARacks

•  CanMalloryusetrickstobreakthealgorithm

•  Therebyreducingthe‘difficulty’ofgemngthekey.

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CipherImplementa+ons

Cryptographyisalwaysanoverhead!!•  Forsecurity,thealgorithmsneedtobecomputaGon

intensive.•  OPenrequirelargenumbers,complexmathemaGcaloperaGons.

•  DesignChallenges:Performance,Size,Power.•  Algorithmstoachievethis

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Implementa+onARacks(SideChannelAnalysis)

Alice Bob

message“A9ackatDawn!!”

untrustedcommunicaGonlink

MallorySideChannelsEg.Powerconsump+on/radia+onofdevice,execu+on+me,etc.

E D

KE KD

“A9ackatDawn!!”encrypGon decrypGon

#%AR3Xf34($(ciphertext)

GetsinformaGonaboutthekeysbymonitoringSidechannelsofthedevice

sidechannels

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SideChannelAnalysis

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Radia+onfromDevice

0 1 1 1Secretinforma+on 0 1

Alice

message“A9ackatDawn!!”

E

00111

encrypGon

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CiphersDesignChallenges

Wewantcryptoalgorithmstobefastandsmall

Forsecurity,thealgorithmsarecomputaGonallyintensive.Typicallyuselargenumbers,complexoperaGons

Needtoprotectagainstsidechannela9acks.

TradeoffsbetweenSecurity,Speed,Side-ChannelARacks

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CryptographyStudy

•  MathemaGcs+EngineeringMathemaGcs ElectricalEngg.

ComputerSc.

cryptography

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Physics

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SomeHotResearchTrends

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lightweightcryptographypost-quantumcryptography

Leakageresilientcryptographysidechannelanalysis

efficientimplementaGons

cryptanalysis

cloudsecurityhomomorphicencrypGon

privacyenhancingsecurity

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ThePlanAhead•  Howareciphersdesigned?

–  IdealsecurityvsComputaGonalsecurity–  Blockciphers/Streamciphers –  AsymmetricKeyciphers–  TradeoffsbetweensecurityandimplementaGon

•  ARacks–  Algorithmic/ImplementaGonbasedA9acks

•  Applica+ons–  HowaretheyusedtoachieveconfidenGality,integrity,authenGcaGon,

non-repudiaGon

•  CaseStudies–  KeyEstablishments,DigitalSignatures,Bitcoins

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CourseStructure•  ClassicalCryptography•  Shannon’sTheory•  BlockCiphers

–  DES,AES,theirimplementaGonsandtheira9acks•  StreamCiphers•  DigitalSignaturesandAuthenGcaGon

–  HashfuncGons•  Publickeyciphers

–  RSA,implementaGons,anda9acks–  ECC

•  Sidechannelanalysis•  CaseStudies:Bitcoins

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ExpectedLearningOutcomes

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•  Whatyouwouldlearnbytheendofthecourse?§  DisGnguishbetweencipheralgorithms

-  Wheretousewhatalgorithm?

§  EvaluateciphersandtheirimplementaGonsforsecurity-  MathemaGcalcryptanalysisofsomealgorithms-  Sidechannelbaseda9acksoncipherimplementaGons

§  Applyalgorithmstosolvesecurityproblemsinreal-worldsystems

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Books/References

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Textbooks (STINSON) ''Cryptography: Theory and Practice", Third Edition, by Douglas R. Stinson, CRC Press, Taylor and Francis Group References (STALLINGS) ''Cryptography and Network Security: Principles and Practices'', Sixth Edition, by William Stallings (HANDBOOK) ''Handbook of Applied Cryptography'', Fifth Printing, by Alfred J. Menezes, Paul C. van Oorschot, and Scott A. Vanstone, CRC Press

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Grading

•  Quiz1:20%on(18/2/2016)•  Quiz2:20%on(25/3/2016)•  Endsemester:30%on(28/4/2016)•  Assignments:15%•  Tutorials:15%

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CourseWebpages

•  Forslides/syllabus/scheduleetc.

•  Fordiscussions/announcements/submissions

CSEMoodleGoogleGroups(aciitm_2017)

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h9p://www.cse.iitm.ac.in/~chester/courses/17e_ac/index.html

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Logis+cs

•  CS36•  Time:

–  Tuesdays:11:00-11:50AM–  Wednesdays:10:00-10:50AM–  Thursdays:8:00-8:50AM–  Fridays:4:50–5:40PM

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