HardwareSecurity

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ChesterRebeiroIITMadras

Physically Unclonable Functions

PhysicalUnclonableFunctionsandApplications:ATutorialhttp://ieeexplore.ieee.org/document/6823677/

EdgeDevices

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1000softhemexpectedtobedeployedLowpower(solarorbatterypowered)SmallfootprintConnectedtosensorsandactuatorsExpectedtooperate24x7almostunmanned24x7thesedeviceswillbecontinuouslypumpingdataintothesystem,whichmayinfluencethewaycitiesoperateWillaffectusinmultipleways,andwemaynotevenknowthattheyexist.

AuthenticatingEdgeDevices•  Storedkeys

–  EEPROMmanufactureisanoverhead–  Publickeycryptographyisheavy–  Canbeeasilycopied/cloned

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EncryptiondoneinedgedevicePublickeysstoredinserver

Privatekeys

PhysicallyUnclonableFunctions•  Nostoredkeys•  Nopublickeycryptography•  Cannotbecloned/copied•  Usesnano-scalevariationsinmanufacture.Notwodevicesareexactlyidentical

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EncryptiondoneinedgedevicePublickeysstoredinserver

challenge/response

DigitalFingerprints

PUFs

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Afunctionwhoseoutputdependsontheinputaswellasthedeviceexecutingit.

WhatisExpectedofaPUF?(InterandIntraDifferences)

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challenge

response

response

challenge

Response

Response

(Reliable)SameChallengetoSamePUFDifferencebetweenresponsesmustbesmallonexpectationIrrespectiveoftemperature,noise,aging,etc.

(Unique)SameChallengetodifferentPUFDifferencebetweenresponsesmustbelargeonexpectationSignificantvariationduetomanufacture

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

Frequencyaffectedbyprocessvariation.

Whyvariationoccurs?

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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

ProcessVariations•  Oxidethickness•  Dopingconcentration•  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

InterChipVariations(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

IntraChipVariations(Reproducabilitymeasurement)

challenge

response

response0.61bitsonaverageoutof128bitsdiffer

120oC1.08V

20oC;1.2V

ArbiterPUF

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0

0

1

10

0

1

1

01

IdeallydelaydifferencebetweenRedandBluelinesshouldbe0iftheyaresymmetricallylaidout.Inpracticevariationinmanufacturingprocesswillintroducerandomdelaysbetweenthetwopaths

Switch

Arbiter

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DFFD

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

GThe image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.

13.56MHzChipForISO14443Aspec.

ResultsforROPUF

18DesignandImplementationofPUF-Based“Unclonable”RFIDICsforAnti-CounterfeitingandSecurityApplicationsIEEEInt.Conf.onRFID,2008,S.Devdaset.Al.

ComparingROandArbiterPUF

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NumberofChallenge:ResponsePairs:

NumberofChallenge:ResponsePairs:

N2

⎛

⎝⎜

⎞

⎠⎟ 2N

#CRPslinearlyrelatedtothenumberofcomponents

#CRPsexponentiallyrelatedtothenumberofcomponents

WEAKPUF STRONGPUF

WeakPUFvsStrongPUF

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•  ComparativelyfewnumberofChallengeResponsePairs(CRPs)

•  HugenumberofChallengeResponsePairs(CRPs)

•  CRPsmustbekeptsecret,becauseanattackermaybeabletoenumerateallpossibleCRPs

•  WeakPUFsusefulforcreatingcryptographickeys

•  ItisassumedthatanattackercannotEnumerateallCRPswithinafixedtimeinterval.ThereforeCRPscanbemadepublic

•  Formally,anadversarygivenapoly-sizedsample

ofadaptivelychosenCRPscannotpredicttheResponsetoanewrandomlychosenchallenge.

•  Typicallyusedalongwithacryptographicscheme(likeencryption/HMACetc)tohidetheCRP(sincetheCRPsmustbekeptsecret)

•  Doesnotrequireanycryptographicscheme,sinceCRPscanbepublic.

WeakPUF StrongPUF

•  VeryGoodInterandIntradifferences

PUFBasedAuthentication(withStrongPUF)

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CRPs

challenge

response

Bootstrapping:Atmanufacture,serverbuildsadatabaseofCRPsforeachdevice.Atdeployment,serverpicksarandomchallengefromthedatabase,queriesthedeviceandvalidatestheresponse

PUFBasedAuthenticationManintheMiddle

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CRPs

challengeresponse

ManinthemiddlemaybeabletobuildadatabaseofCRPsTopreventthis,CRPsarenotusedmorethanonce

PUFBasedAuthenticationCRPTables

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CRPs

challengeresponse

EachdevicewouldrequireitsownCRPtableandsecurelystoredinatrustedserver.Tablesmustbelargeenoughtocatertotheentirelifetimeofthedeviceorneedstoberechargedperiodically(scalabilityissues)

CRPs

PUFbasedAuthentication(AlleviatingCRPProblem)

SecretModelofPUF

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GateDelaysofPUFcomponents Bootstrapping:Atmanufacture,serverbuildsa

databaseofgatedelaysofeachcomponentinthePUF.Atdeployment,serverpicksarandomchallengeconstructsitsexpectedresponsefromsecretmodel,queriesthedeviceandvalidatestheresponse

StillRequiresSecureBootstrapping

andSecureStorage

PUFbasedAuthentication(AlleviatingCRPProblem)

•  PPUF:PublicModelPUF

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GateDelaysofPUFComponents(Public)

Trustedserver(PKI)

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

Assumption:AdevicetakesmuchlesstimetocomputeaPUFresponsethananattackerwhomodelsthePUF.

T<T0?

PUFbasedAuthentication(AlleviatingCRPProblem)

HomomorphicEncryption

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EncryptedCRPs

UntrustedCloud

Response

Conclusions•  DifferenttypesofPUFsbeingexplored

–  AnalogPUFs,SensorPUFsetc.

•  CRPissuestillabigproblem

•  SeveralattacksfeasibleonPUFs.–  Modelbuildingattacks(SVMs)–  TamperingwithPUFcomputation(eg.Forcingasine-waveonthegroundplane,

canaltertheresultsofthePUF)

•  PUFsareaverypromisingwayforlightweightauthenticationofedgedevices.

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HardwareTrojans

Hardware Security: Design, Threats, and Safeguards; D. Mukhopadhyay and R.S. Chakraborty Slides from R. S. Chakraborty, Jayavijayan Rajendran, Adam Waksman

HardwareTrojan

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•  MaliciousanddeliberatelystealthymodificationmadetoanelectronicdevicesuchasanIC

•  ItcanchangethechipsfunctionalitytherebyunderminetrustinsystemsthatusethisIC

cryptoModule

key

inputciphertext

HardwareTrojan

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•  MaliciousanddeliberatelystealthymodificationmadetoanelectronicdevicesuchasanIC

•  ItcanchangethechipsfunctionalitytherebyunderminetrustinsystemsthatusethisIC

cryptoModule

key

inputciphertext

1

0

cryptoModule

key

inputciphertext

ExampleofaHardwareTrojanCheatCode(combinationaltrojans)

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Trigger

If(input==0xcafebeef)select=1elseselect=0

PropertiesofHardwareTrojan:•  verysmall•  mostlypassive

0xcafebeef1

0

cryptoModule

key

inputciphertext

ExampleofaHardwareTrojanSequentialTrojan(Timebombs)

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Trigger

PropertiesofHardwareTrojan:•  verysmall•  mostlypassive

0xca0xaf0xee0xbe0xef

1

0

time

select=1select=0ca

af

eebe

ef

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

*http://www.darpa.mil/MTO/solicitations/baa07-24/index.html

Offshore

Third-party

PropertiesofHardwareTrojan:*verysmall•  mostlypassive•  Canbeaddedatmultiplestages

HardwareTrojanStructure

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PayloadTriggerCircuit

TriggerCircuit:Basedonaseldomoccurringevent.Forexample,•  whenaddressonaddressbusis0xdeadbeef.•  Aparticularlyrarepacketarrivesonnetwork•  Sometimehaselapsed

Payload:Dosomethingnefarious:•  Makeapageinmemory(un)privileged•  Leakinformationtotheoutsideworldthroughnetwork,

covertchannels,etc•  Causethesystemtofail

Trojancanbeinsertedanywhereinduringthemanufacturingprocess(eg.InthirdpartyIPcorespurchased,byfabricationplant,etc.)

TrojansinIPs•  ThirdpartyIPs

–  Cantheybetrusted?–  Willtheycontainmalicious

backdoors

•  Developersdon’t/can’tsearch1000soflinesofcodelookingoutfortrojans.

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FANCI:IdentificationofStealthyMaliciousLogic

•  FANCI:evaluatehardwaredesignsautomaticallytodetermineifthereisanypossiblebackdoorshidden

•  Thegoalistopointouttotestersofpossibletrojanlocationsinahugepieceofcode

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http://www.cs.columbia.edu/~simha/preprint_ccs13.pdf(someofthefollowingslidesareborrowedfromAdamWaksman’sCCStalk)

BackdoorsareStealthy•  Small

–  Typicallyafewlinesofcode/area•  Stealth

–  Cannotbedetectedbyregulartestingmethodologies(raretriggers)–  Passivewhennottriggered

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Unfortunately…Withsomuchofcodeitishighlylikelythatstealthyportionsofthecodearemissedornottestedproperly.

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FANCI:willdetectthesestealthycircuits.ThesepartsaremostlikelytohaveTrojans.Theaimistohavenofalsenegatives.Afewfalsepositivesareacceptable

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 1 039

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 1 040

Byhowmuchdoesainputinfluencetheoutput0?

A:hasacontrolof0.5ontheoutput(Amattersinthisfunction)

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 1 041

Byhowmuchdoesainputinfluencetheoutput0?

A:hasacontrolof0ontheoutput(Adoesnotmatterinthisfunction)(Aiscalledunaffecting)

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

A31hasacontrolvalue1/216

EasiertohideatrojanwhenlargerinputsetsareconsideredAlowchanceofaffectingtheoutputLendsitselftostealthinessàeasiertohideamaliciouscode

AnExampleofaMux

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<A,B,C,D,S1,S2>=<0.25,0.25,0.25,0.25,0.5,0.5>

Notrojanpresenthere(intutively):*Allmuxinputshaveacontrolvaluearoundmidrange(nottoocloseto0)

AnExampleofaMaliciousMux

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66extraselectlineswhichareonlymodifyMwhenwheyaresettoaparticularvalue

M

ThecontrolvaluesEandS3toS66aresuspiciousbecausetheyrarelyinfluencethevalueofM.Perfectfordisguisingmaliciousbackdoors

JustsearchingforMINvaluesisoftennotenough.Bettermetricsareneeded.

ComputingStealthfromControl

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ComputingStealthfromControl

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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

*http://www.darpa.mil/MTO/solicitations/baa07-24/index.html

Third-party

DetectingTrojansinICs•  OpticalInspectionbasedtechniques

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

–  Drawbacks:CostandTime!

•  Testingtechniques–  Notaverypowerfultechnique

•  Sidechannelbasedtechniques–  Nonintrusivetechnique–  Compareside-channelswithagoldenmodel

49ASurveyonHardwareTrojanDetectionTechniqueshttp://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7169073

SideChannelBasedTrojanDetection

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LightweightPRESENTImplementation PowerTraces

Hardwaretrojandesignanddetection:apracticalevaluationhttps://dl.acm.org/citation.cfm?id=2527318

SideChannelBasedTrojanDetection(ICwithTrojan)

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DifferenceofDistributions

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HardwareTrojanPrevention(Ifyoucan’tdetectthenprevent)

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

HardwareTrojanPrevention

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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(withObfuscation)

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SilencingTickingTimebombs•  PowerResets:flushpipeline,writecurrentIPandregistersto

memory,savebranchhistorytargets

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SilencingTickingTimebombs•  Cantriggerbestoredtoarchitecturalstateandrestoredlater

–  No.Unitvalidationtestspreventthis–  Reasonfortrustingvalidationepoch

LargevalidationteamsOrganizedhierarchically

•  Cantriggersbestoredinnon-volatilestateinternaltotheunit?–  Eg.Malwareconfiguresahiddennon-volatilememory

•  UnmaskableInterrupts?–  UseaFIFOtostoreunmaskableinterrupts

•  PerformanceCountersarehiddentimebombs 65

DataObfuscation

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HomomorphicEncryption(Gentry2009)IdealsolutionButpracticalhurdles

DataObfuscation

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DataObfuscation

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StoreData5toAddress7

DataObfuscation(ComputationalCase)

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SequenceBreaking(Reordering)

70Ensurefunctionalityismaintained

SequenceBreaking(Insertingevents)

71Insertarbitraryeventswhenreorderingisdifficult

CatchAll(Duplication)

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Expensive:Non-recurring:design;verificationcostsduetoduplicationRecurring:Powerandenergycosts

PowerAnalysis

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CMOSTechnology•  AlmosteverydigitaldeviceisbuiltusingCMOS

technology.•  CMOS–complimentarymetaloxide

semiconductor

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CMOSInverter

•  Whentheinputswitchesfrom0à1,TransistorT1turnsonandT2turnsoff.CapcitorCLgetscharged.

•  Whentheinputswitchsfrom1à0,transitorT1isturnedoffandT2turnson.CapacitorCLdischarges.

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T1

T2

PowerConsumptionofaCMOSInverter

•  PowerisconsumedwhenCLchargesordischarges(i.e.thereisatransitionintheoutputfrom0à1or1à0)

•  Usinganoscilloscopewecanmeasurethepowertodeterminewhentheinverteroutputchangesstate

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Outputofinverter

Powerconsumption

SynchronousDigitalCircuits•  Mostelectronicequipmentuseaclockasreference•  Allstatetransitionsaredonewithrespecttothisclock

–  Powerconsumptionisthereforeatclockedges

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EssenceofPowerAnalysis•  Wedon’tknowwhatishappeninginsidethedevice,butweknowthepower

consumption•  Canwededucesecretinformationfromthepowerconsumption

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TheTypesofPowerAnalysis•  SPA:SimplePowerAnalysis

•  DPA:DifferentialPowerAnalysis

Requiresmorestrategyandstatisticstogleansecretinformation

•  Templatebasedattacks

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DifferentialPowerAnalysis(asaglance)

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Inputdata

Key

Guessedkey

deviceundertest

Modelof

device

StatisticallyCompare

Powerconsumption Hypotheticalpowerconsumption

HypotheticalPowerConsumption•  CMOScircuitsfollowtheHammingweightandHammingdistancepower

models•  HammingDistanceModel

–  ConsidertransitionsofregisterR

•  HammingWeightModel

TheHammingweightmodelwillwork,whenRisprechargedtoeither0or1

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K

P CFR

(1011)à(1101)à(1001)à(0010)à(0011)3131#toggles

(1011)à(1101)à(1001)à(0010)à(0011)3213#toggles

ASmallExample

P K C

0000 1010 1010

0001 1010 1011

0010 1010 1000

0011 1010 1001

0100 1010 1110

0101 1010 1111

.. … …82

K

P C

Device

Malloryhascontrolofthisdevice.--Shecanmonitoritspowerconsumption--ShecanfeedinputsP--Sheevenknowswhatoperationsgoesoninside.Thethingsshedoesn’tknowisKandCHeraimistoobtainthesecretkeyK

F

DPAAttack

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P Kguess C HypotheticalPower

RealPowerMeasured

0000 1111 1111 4

0001 1111 1110 3

0010 1111 1101 3

0011 1111 1100 2

0100 1111 1011 3

0101 1111 1010 2

⁞ ⁞ ⁞ ⁞ ⁞

notethatthisisawaveformwhichchangesw.r.ttime

P=0000

P=0001

P=0010Chereiscomputedwrttotheguessedkeyi.e.C=F(P,Kguess)

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DPA:WhatwemeanbycorrelationHypotheticalPower

4

3

3

Thesewaveformsarediscrete,theyhaveseveralpointsPerformcorrelationofhypotheticalPowerwrteachpointinthewaveformsConsideronlythemaximumcorrelation

correlate

DPA:Asmallexample

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P Kguess C HypotheticalPower

RealPowerMeasured

0000 1111 1111 4 xx

0001 1111 1110 3 xx

0010 1111 1101 3 xx

0011 1111 1100 2 xx

0100 1111 1011 3 xx

0101 1111 1010 2 xx

⁞ ⁞ ⁞ ⁞ ⁞

correlate

ρ15

P Kguess C HypotheticalPower

RealPowerMeasured

0000 1110 1110 3 xx

0001 1110 1111 4 xx

0010 1110 1100 2 xx

0011 1110 1101 3 xx

0100 1110 1010 2 xx

0101 1110 1011 3 xx

⁞ ⁞ ⁞ ⁞ ⁞correlate

ρ14

P Kguess C HypotheticalPower

RealPowerMeasured

0000 1101 1101 3 xx

0001 1101 1100 2 xx

0010 1101 1111 4 xx

0011 1101 1110 3 xx

0100 1101 1001 2 xx

0101 1101 1000 1 xx

⁞ ⁞ ⁞ ⁞ ⁞correlate

ρ13 ρ12 ρ11 ρ10Findmaximumcorrelation

SampleOutput

86https://iis-people.ee.ethz.ch/~kgf/acacia/acacia.html

StatisticalComparison•  Correlation:

Providesavaluebetween-1and+1.Avalueclosertothesignifieslineardependencebetweenthehypotheticalpowerandtherealpowerconsumption

•  MutualInformationQuantifiesmutualdependencebetweenhypotheticalpowerandrealpowerconsumption

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StatisticalComparison•  BayesAnalysisWhatistheprobabilityofahypothesisgivenaspecificleakage

Pr[Hypothesis|Leakage]•  DifferenceofMeansnext…

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DifferenceofMeans•  Guessakey:kguess•  ComputeCguess=F(P,Kguess)•  Findthekguesssuchthat|AVG(B0)–AVG(B1)|ismaximum

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Device

B0 B1

BIT(Cguess,0)=0

P=0000Cguess=1111

P=0001Cguess=1110

P=0010Cguess=1101

K

P CF

BIT(Cguess,0)=1

PreventingDPA•  Byhardwaremeans

–  Differentiallogic•  ByImplementation

–  Masking

•  ByAlgorithm–  DPAresistantciphers(DRECON)–  Rekeying

90