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WatermarkingTechniquesforElectronicCircuitDesignEdoardoCharbon1andIlhamiTorunoglu21SwissFederalInstituteofTecnology,Lausanne,Switzerlandedoardo.charbon@epfl.ch2CanestaInc.,SanJose,CaliforniaU.S.A.ilhami@canesta.comAbstract.Enforcingcopyrightlawsrelatedtocircuitdesignisusuallyhard,sincediscoveryandproofofinfringementsarerequiredbeyondrea-sonabledoubt.Provingthatagivencircuitryistriviallyderivedfromapatentedtechniqueormethodisingeneralapainstakinglyslowtask,oftenrequiringreverse-engineeringandforensicanalysisoffabricatedchips.Thesetechniquesaresocomplexthattheirapplicationtolargecollectionsofcommercialproductsisalmostalwaysprohibitive.Water-markingisoneofseveraltechniquesavailabletodaytodetercopyrightinfringementinelectronicsystems.Thetechniqueconsistsofimplantingindeliblestampsinthecircuit'sinnerstructure,whilenotdisruptingitsfunctionalityorsigni cantlydegradingitsperformance.Inthispaperaseriesofmethodsisproposedforthecreationofwatermarksatseveralstagesofthedesigncycle,fromhigh-leveldesigntolayout.Algorithmsaredescribedforimplantingrobustwatermarkstominimizetheover-headand,ultimately,toreducetheimpactonperformance.Detectionmethodsarediscussedinthepresenceofinfringement.Theresilienceofthemethodsinseveraltamperingregimesisestimated.1IntroductionWiththeintroductionoflarge-scalesystem-on-chip(SOC)designparadigms,theVLSIsemiconductorindustryisundergoingarevolution.Asaconsequence,asigni cantincreaseinoperatingspeedsanddesignproductivityisexpected.Circuitcomponentswillbeavailabletointegratorsinelectronicformratherthaninsilicon.Suchcomponents,knownasvirtualcomponents,willbedeliveredforaparticularapplicationaccordingtoaspeci ccontract.Duetothenewmediumofstorageandexchange,virtualcomponentsarepronetoinfringementsandabuses,i.e.usesbeyondtheoriginalcontractsand/orbyunauthorizedintegra-tors.ProtectingtheIntellectualProperty(IP)rightsoftheauthorsofvirtualcomponentisanemergingmulti-disciplinary eldencompassingseveralaspectsoftoday'sICdesignprocess.Existinglegaldevices,suchaspatents,tradesecrets,copyrights,andnon-disclosureagreementsareaimedatdeterringpotentialinfringement.However,therealAchille'shealofthesystemiscurrentlytheenforcementofsuchrights.ThegoalofIPprotectionasawholeistoprovidenecessarytechnologiestomakeenforcementamoremanageabletaskwhiledeterringinfringementatalllevelsofadesign.Apossiblesuchschemerequiresthecapabilityofe ectivelydetectingandsubsequentlytrackingIPinfringementcases.Thistaskcanbeaccomplishedbyaprocessknownaswatermarking.Themethodconsistsofem-beddingauniquecode,orwatermark,whichexploitstheIP'suniquefeatures.Fundamentalrequirementsforawatermarkarethatitbe(1)transparent,i.e.notinterferingwiththedesignfunctionality,(2)robust,i.e.hardtoremoveorforge,(3)detectable,i.e.easytoextractfromthedesign.Theprocessusedformanagingwatermarksmustnotnecessarilybeproprietary,whilethecodeusedintheencryptionprocessshouldbesecretforanyreleasedIP.Thereexistthreebasictypesofvirtualcomponent,basedonitscharacteriza-tionthrough(a)behavioraldescription(softIP),(b)structuraldescription( rmIP),and(c)physicaldescription(hardIP).HardIPsaregenerallyreleasedasaplug-and-playcomponentforoneormoretechnologies,while rmandsoftIPsarepartiallyimplementedversionsofadesign,thusanumberofdegreesoffree-domarestillavailabletotheintegratorandpotentiallyalltechnologiescanbeusedforimplementation.DuetothediversityoftheimplementationlandscapeofIPs,theirprotectionisalsoacomplextask.Recently,watermarkinghasbeenproposedtoprotectdigitalaudio-visualIPs.Theliteratureisveryextensiveonthesubject.Herewementiononlytwoworks[1,2]becausetheyallowustointroducesomeofthetechniquesusedinthispaper.Themainmethoddescribedin[1,2],thoughwithsmallvariations,essentiallyconsistofsuperimposingapseudo-randomnoisetothesignaloftherecord.Suchnoise,thoughcompletelyinaudible,canbeeasilydetectedviadigitalsignalprocessingmethods.SchemesbasedonwatermarkinghavebeenrecentlyproposedforelectronicIPsaswell.In[3,4]thewatermarkassumestheformofaextraneousbitstream,hiddeninsidelargeFieldProgrammableGateArrays(FPGAs).Thewatermarkisstoredinsomeoftheunusedcon gurablecontrollogicblocksoftheFPGA.Eachunusedlookuptableisresponsibleforstoringasinglebitinthecode.Allthecon gurablecontrolelementsusedinthewatermarkarethenroutedinthedesignformimeticpurposes.Thisisdoneinsuchamannertoavoidanyimpactontheoriginalfunctionality.Themethodhaslaterbeenre nedin[5]wherethesignatureismodi edbeforebeingembeddedsoastomimicthestatisticalpropertiesoftheexistingdesign,hencereducingdetectability.Oneissueinouropinionstillremaininginthisapproachisthefactthattodatewatermarkedlookuptablesdonotreectanyfunctionality,thusrepresentingapotentialweakpointinthescheme.In[6,7]itwasproposedtoincorporateseveralwatermarks,distributedoveralltheabstractionlevelsofagivendesign.Thetechniquesdi erdependingontheabstractionleveltheyareapplicableto.Atthephysicaldesignlevel,thewatermarkassumestheformofasetoftopologicalconstraintsgoverningtherelativeposition,orientation,and,possibly,scalingofthedevicesorgatesofthecircuit.AtstructuralandRTLlevel,const