HardwareSecurity

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ChesterRebeiroIITMadras

Physically Unclonable Functions

PhysicalUnclonableFunc1onsandApplica1ons:ATutorialh8p://ieeexplore.ieee.org/document/6823677/

EdgeDevices

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1000softhemexpectedtobedeployedLowpower(solarorba8erypowered)SmallfootprintConnectedtosensorsandactuatorsExpectedtooperate24x7almostunmanned24x7thesedeviceswillbecon1nuouslypumpingdataintothesystem,whichmayinfluencethewayci1esoperateWillaffectusinmulRpleways,andwemaynotevenknowthattheyexist.

AuthenRcaRngEdgeDevices•  Storedkeys

–  EEPROMmanufactureisanoverhead–  Publickeycryptographyisheavy–  Canbeeasilycopied/cloned

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EncrypRondoneinedgedevicePublickeysstoredinserver

Privatekeys

PhysicallyUnclonableFuncRons•  Nostoredkeys•  Nopublickeycryptography•  Cannotbecloned/copied•  Usesnano-scalevariaRonsinmanufacture.NotwodevicesareexactlyidenRcal

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EncrypRondoneinedgedevicePublickeysstoredinserver

challenge/response

DigitalFingerprints

PUFs

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AfuncRonwhoseoutputdependsontheinputaswellasthedeviceexecuRngit.

WhatisExpectedofaPUF?(InterandIntraDifferences)

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challenge

response

response

challenge

Response

Response

(Reliable)SameChallengetoSamePUFDifferencebetweenresponsesmustbesmallonexpectaRonIrrespecRveoftemperature,noise,aging,etc.

(Unique)SameChallengetodifferentPUFDifferencebetweenresponsesmustbelargeonexpectaRonSignificantvariaRonduetomanufacture

WhatisExpectedofaPUF?(Unpredictability)

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challenge

response

response

DifficulttopredicttheoutputofaPUFtoarandomlychosenchallengewhenonedoesnothaveaccesstothedevice

IntrinsicPUFs•  Completelywithinthechip

–  PUF–  Measurementcircuit–  Post-processing

•  Nofancyprocessingsteps!–  eg.MostSiliconbasedPUFs

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SiliconPUFseg.RingOscillatorPUF

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f = 12nt

FrequencyofringoscillatorNumberofstagesDelayofeachstage

fnt

RingOscillatorwithoddnumberofgates

FrequencyaffectedbyprocessvariaRon.

WhyvariaRonoccurs?

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Whengate voltage is less than threshold no current flows When gate voltate is greater than threshold current flows from source to drain Threshold voltage is a function of doping concentration, oxide thickness

Delaydependsoncapacitance

ProcessVaria1ons•  Oxidethickness•  DopingconcentraRon•  Capacitance

MOSTransistor CMOSInverter

SiliconPUFseg.RingOscillatorPUF

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>enable

counter

counter

Nbitchallenge

1

2

3

N

N-1

N-2

1bitresponse

RA

RB

response = 10

fA > fBfA ≤ fB

⎧⎨⎪

⎩⎪

ResultsofaROPUF15Xilinx,Virtex4FPGAs;1024ROsineachFPGA;EachROhad5inverterstagesand1ANDgate

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Physical Unclonable Functions for Device Authentication and Secret Key Generation https://people.csail.mit.edu/devadas/pubs/puf-dac07.pdf

InterChipVaria1ons(Uniquenessmeasurement)

challenge

response

responseWhen128bitsareproduced,

Avg59.1bitsoutof128bitsdifferent

ResultsofaROPUF15Xilinx,Virtex4FPGAs;1024ROsineachFPGA;EachROhad5inverterstagesand1ANDgate

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Physical Unclonable Functions for Device Authentication and Secret Key Generation https://people.csail.mit.edu/devadas/pubs/puf-dac07.pdf

IntraChipVaria1ons(Reproducabilitymeasurement)

challenge

response

response0.61bitsonaverageoutof128bitsdiffer

120oC1.08V

20oC;1.2V

ArbiterPUF

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0

0

1

1

0

0

1

1

01

IdeallydelaydifferencebetweenRedandBluelinesshouldbe0iftheyaresymmetricallylaidout.InpracRcevariaRoninmanufacturingprocesswillintroducerandomdelaysbetweenthetwopaths

Switch

Arbiter

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DFF

D

clk

Q ?

IfthesignalatDreachesfirstthenQwillbesetto1IfthesignalatclkreachesfirstthenQwillbesetto0

DFF

ArbiterPUF

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…

challenge

rising Edge

1 if toppath is faster,else 0

D Q1

1

0

0

1

1

0

0

1

1

0

0

1 0 10 0 1

01

G

13.56MHzChipForISO14443Aspec.

ResultsforROPUF

18DesignandImplementa1onofPUF-Based“Unclonable”RFIDICsforAn1-Counterfei1ngandSecurityApplica1onsIEEEInt.Conf.onRFID,2008,S.Devdaset.Al.

ComparingROandArbiterPUF

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NumberofChallenge:ResponsePairs:

NumberofChallenge:ResponsePairs:

N2

⎛

⎝⎜

⎞

⎠⎟ 2N

#CRPslinearlyrelatedtothenumberofcomponents

#CRPsexponenRallyrelatedtothenumberofcomponents

WEAKPUF STRONGPUF

WeakPUFvsStrongPUF

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•  ComparaRvelyfewnumberofChallengeResponsePairs(CRPs)

•  HugenumberofChallengeResponsePairs(CRPs)

•  CRPsmustbekeptsecret,becauseana8ackermaybeabletoenumerateallpossibleCRPs

•  WeakPUFsusefulforcreaRngcryptographickeys

•  Itisassumedthatana8ackercannotEnumerateallCRPswithinafixedRmeinterval.ThereforeCRPscanbemadepublic

•  Formally,anadversarygivenapoly-sizedsampleofadapRvelychosenCRPscannotpredictthe

Responsetoanewrandomlychosenchallenge.

•  Typicallyusedalongwithacryptographicscheme(likeencrypRon/HMACetc)tohidetheCRP(sincetheCRPsmustbekeptsecret)

•  Doesnotrequireanycryptographicscheme,sinceCRPscanbepublic.

WeakPUF StrongPUF

•  VeryGoodInterandIntradifferences

PUFBasedAuthenRcaRon(withStrongPUF)

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CRPs

challenge

response

Bootstrapping:Atmanufacture,serverbuildsadatabaseofCRPsforeachdevice.Atdeployment,serverpicksarandomchallengefromthedatabase,queriesthedeviceandvalidatestheresponse

PUFBasedAuthenRcaRonManintheMiddle

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CRPs

challenge

response

ManinthemiddlemaybeabletobuildadatabaseofCRPsTopreventthis,CRPsarenotusedmorethanonce

PUFBasedAuthenRcaRonCRPTables

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CRPs

challenge

response

EachdevicewouldrequireitsownCRPtableandsecurelystoredinatrustedserverTablesmustbelargeenoughtocatertotheenRrelifeRmeofthedeviceorneedtoberechargedperiodically(scalabilityissues)

CRPs

PUFbasedAuthenRcaRon(AlleviaRngCRPProblem)

SecretModelofPUF

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GateDelaysofPUFcomponents Bootstrapping:Atmanufacture,serverbuildsa

databaseofgatedelaysofeachcomponentinthePUF.Atdeployment,serverpicksarandomchallengeconstructsitsexpectedresponsefromsecretmodel,queriesthedeviceandvalidatestheresponse

SRllRequiresSecureBootstrapping

andSecureStorage

PUFbasedAuthenRcaRon(AlleviaRngCRPProblem)

•  PPUF:PublicModelPUF

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GateDelaysofPUFComponents(Public)

Trustedserver(PKI)

Bootstrapping:DownloadthepublicmodelofPUFfromthetrustedserver.Atdeployment,serverpicksarandomchallengeconstructsexpectedresponsefrompublicmodel,queriesthedeviceandvalidatestheresponse.IfRmeforresponseislessthanathresholdacceptresponseelserejects.

AssumpRon:AdevicetakesmuchlessRmetocomputeaPUFresponsethanana8ackerwhomodelsthePUF.

T<T0?

PUFbasedAuthenRcaRon(AlleviaRngCRPProblem)

HomomorphicEncryp1on

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EncryptedCRPs

UntrustedCloud

Response

Conclusions•  DifferenttypesofPUFsbeingexplored

–  AnalogPUFs,SensorPUFsetc.

•  CRPissuesRllabigproblem

•  Severala8acksfeasibleonPUFs.–  Modelbuildinga8acks(SVMs)–  TamperingwithPUFcomputaRon(eg.Forcingasine-waveontheground

plane,canaltertheresultsofthePUF)

•  PUFsareaverypromisingwayforlightweightauthenRcaRonofedgedevices.

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HardwareTrojans

Hardware Security: Design, Threats, and Safeguards; D. Mukhopadhyay and R.S. Chakraborty

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h8ps://www.theguardian.com/technology/2012/may/29/cyber-a8ack-concerns-boeing-chiph8ps://techcrunch.com/2013/09/05/nsa-subverts-most-encrypRon-works-with-tech-companies-for-back-door-access-report-says/h8ps://www.theregister.co.uk/2013/07/29/lenovo_accused_backdoors_intel_ban/h8ps://www.technologyreview.com/s/519661/nsas-own-hardware-backdoors-may-sRll-be-a-problem-from-hell/

ICLifeCycle(VulnerableSteps)

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IP ToolsStd. Cells Models

DesignSpecifications Fab Interface Mask Fab

WaferProbe

Dice and Package

PackageTest

Deploy and

Monitor

Trusted

Either

Untrusted

Wafer

*hbp://www.darpa.mil/MTO/solicita1ons/baa07-24/index.html

Offshore

Third-party

MalwareinThirdPartyIPs

•  ThirdpartyIPs–  Cantheybetrusted?– Willtheycontainmaliciousbackdoors

•  Developersdon’t/can’t

search1000soflinesofcodelookingoutfortrojans.

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FANCI:IdenRficaRonofStealthyMaliciousLogic

•  FANCI:evaluatehardwaredesignsautomaRcallytodetermineifthereisanypossiblebackdoorshidden

•  ThegoalistopointouttotestersofpossibletrojanlocaRonsinahugepieceofcode

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h8p://www.cs.columbia.edu/~simha/preprint_ccs13.pdf(someofthefollowingslidesareborrowedfromWaksman’sCCStalk)

HardwareTrojanStructure

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PayloadTriggerCircuit

TriggerCircuit:Basedonaseldomoccurringevent.Forexample,•  whenaddressonaddressbusis

0xdeadbeef.•  AparRcularlyrarepacketarriveson

network•  SomeRmehaselapsed

Payload:Dosomethingnefarious:•  Makeapageinmemory(un)privileged•  LeakinformaRontotheoutsideworld

throughnetwork,covertchannels,etc•  Causethesystemtofail

Trojancanbeinsertedanywhereinduringthemanufacturingprocess(eg.InthirdpartyIPcorespurchased,byfabricaRonplant,etc.)

Trojan=Trigger+Payload

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Trojan=Trigger+Payload

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BackdoorsareStealthy

•  Small–  Typicallyafewlinesofcode/area

•  Stealth–  CannotbedetectedbyregulartesRngmethodologies(raretriggers)

–  Passivewhennottriggered

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Unfortunately…

WithsomuchofcodeitishighlylikelythatstealthyporRonsofthecodearemissedornottestedproperly.

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FANCI:willdetectthesestealthycircuits.Thesepartsaremostlikelyto

haveTrojans.TheaimistohavenofalsenegaRves.AfewfalseposiRvesareacceptable

ControlValues

A B C O

0 0 0 0

0 0 1 1

0 1 0 1

0 1 1 0

1 0 0 1

1 0 1 1

1 1 0 0

1 1 1 038

ByhowmuchdoesaninputinfluencetheoutputO?

A

B

C

O

ControlValues

A B C O

0 0 0 0

1 0 0 1

0 0 1 1

1 0 1 1

0 1 0 1

1 1 0 0

0 1 1 0

1 1 1 039

Byhowmuchdoesainputinfluencetheoutput0?

A:hasacontrolof0.5ontheoutput(Ama8ersinthisfuncRon)1 1 0 0A B C 0

A

B

C

O

ControlValues

A B C O

0 0 0 0

1 0 0 0

0 0 1 1

1 0 1 1

0 1 0 0

1 1 0 0

0 1 1 0

1 1 1 040

Byhowmuchdoesainputinfluencetheoutput0?

A:hasacontrolof0ontheoutput(Adoesnotma8erinthisfuncRon)(AiscalledunaffecRng)

1 1 0 0A B C 0

A

B

C

O

ControlValuesforaTriggerinaTrojan

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if (addr == 0xdeadbeee) then{ trigger = 1 }

A31 A30 A2 A1 A0 trigger

0 0 … 0 0 0 0

0 0 … 0 0 1 0

0 0 … 0 1 0 0

0 0 … 0 1 1 0

: : : : : :

1 1 1 1 0 1

: : : : : :

1 1 1 1 1 1 0

A31hasacontrolvalue1/232

EasiertohideatrojanwhenlargerinputsetsareconsideredAlowchanceofaffecRngtheoutputLendsitselftostealthinessàeasiertohideamaliciouscode

AnExampleofaMux

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<A,B,C,D,S1,S2>=<0.25,0.25,0.25,0.25,0.5,0.5>Notrojanpresenthere(intuRvely):*Allmuxinputshaveacontrolvaluearoundmidrange(nottoocloseto0)

AnExampleofaMaliciousMux

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66extraselectlineswhichareonlymodifyMwhenwheyaresettoaparRcularvalue

M

ThecontrolvaluesEandS3toS66aresuspiciousbecausetheyrarelyInfluencethevalueofM.Perfectfordisguisingmaliciousbackdoors

JustsearchingforMINvaluesisowennotenough.Be8ermetricsAreneeded.

CompuRngStealthfromControl

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CompuRngStealthfromControl

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FANCI:TheCompleteAlgorithm

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ICLifeCycle(TheFab)

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IP ToolsStd. Cells Models

DesignSpecifications Fab Interface Mask Fab

WaferProbe

Dice and Package

PackageTest

Deploy and

Monitor

Trusted

Either

Untrusted

Wafer

*hbp://www.darpa.mil/MTO/solicita1ons/baa07-24/index.html

Offshore

Third-party

DetecRngTrojansinICs•  OpRcalInspecRonbasedtechniques

ScanningOpRcalMicroscopy(SOM),ScanningElectronMicroscopy(SEM),andpico-secondimagingcircuitanalysis(PICA)

–  Drawbacks:CostandTime!

•  TesRngtechniques–  Notaverypowerfultechnique

•  Sidechannelbasedtechniques–  Nonintrusivetechnique–  Compareside-channelswithagoldenmodel

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ASurveyonHardwareTrojanDetecRonTechniquesh8p://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7169073

SideChannelBasedTrojanDetecRon

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LightweightPRESENTImplementaRonPowerTraces

Hardwaretrojandesignanddetec1on:aprac1calevalua1onh8ps://dl.acm.org/citaRon.cfm?id=2527318

SideChannelBasedTrojanDetecRon(ICwithTrojan)

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DifferenceofDistribuRons

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HardwareTrojanPrevenRon(Ifyoucan’tdetectthenprevent)

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SilencingHardwareBackdoorswww.cs.columbia.edu/~simha/preprint_oakland11.pdfSlidestakenfromAdamWaksman’sOaklandtalk

HardwareTrojanPrevenRon

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EnsurethatahardwareTrojanisneverdeliveredthecorrectTrigger

Example(A5stageprocessor)

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Example(A5stageprocessor)

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TypesofTrojans

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TickingTimebomb

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TickingTimebomb

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CheatCodes

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CheatCodes

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SequenceCheatCodes

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HardwareTrojanSilencing(withObfuscaRon)

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SilencingTickingTimebombs•  PowerResets:flushpipeline,writecurrentIPandregistersto

memory,savebranchhistorytargets

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SilencingTickingTimebombs•  Cantriggerbestoredtoarchitecturalstateandrestoredlater

–  No.UnitvalidaRontestspreventthis–  ReasonfortrusRngvalidaRonepoch

LargevalidaRonteamsOrganizedhierarchically

•  Cantriggersbestoredinnon-volaRlestateinternaltotheunit?–  Eg.Malwareconfiguresahiddennon-volaRlememory

•  UnmaskableInterrupts?–  UseaFIFOtostoreunmaskableinterrupts

•  PerformanceCountersarehiddenRmebombs

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DataObfuscaRon

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HomomorphicEncrypRon(Gentry2009)IdealsoluRonButpracRcalhurdles

DataObfuscaRon

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DataObfuscaRon

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StoreData5toAddress7

DataObfuscaRon(ComputaRonalCase)

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SequenceBreaking(Reordering)

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EnsurefuncRonalityismaintained

SequenceBreaking(InserRngevents)

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Insertarbitraryeventswhenreorderingisdifficult

CatchAll(DuplicaRon)

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Expensive:Non-recurring:design;verificaRoncostsduetoduplicaRonRecurring:Powerandenergycosts