文献翻译——数字水印

第1页外文文献资料DigitalWatermarkingNasirMemonDepartmentofComputerScienceStevensInstituteofTechnologyPolytechnicUniversityHobokenNJ,07030Brooklyn,NY112011.IntroductionTheadventoftheInternethasresultedinmanynewopportunitiesforthecreationanddeliveryofcontentindigitalform.Applicationsincludeelectronicadvertising,realtimevideoandaudiodelivery,digitalrepositoriesandlibraries,andWebpublishing.Animportantissuethatarisesintheseapplicationsistheprotectionoftherightsofallparticipants.Ithasbeenrecognizedforquitesometimethatcurrentcopyrightlawsareinadequatefordealingwithdigitaldata.Thishasledtoaninteresttowardsdevelopingnewcopydeterrenceandprotectionmechanisms.Onesucheffortthathasbeenattractingincreasinginterestisbasedondigitalwatermarkingtechniques.Digitalwatermarkingistheprocessofembeddinginformationintodigitalmultimediacontentsuchthattheinformation(whichwecallthewatermark)canlaterbeextractedordetectedforavarietyofpurposesincludingcopypreventionandcontrol.Digitalwatermarkinghasbecomeanactiveandimportantareaofresearch,anddevelopmentandcommercializationofwatermarkingtechniquesisbeingdeemedessentialtohelpaddresssomeofthechallengesfacedbytherapidproliferationofdigitalcontent.Intherestifthischapterweassumethatthecontentbeingwatermarkedisastillimage,thoughmostdigitalwatermarkingtechniquesare,inprinciple,equallyapplicabletoaudioandvideodata.Adigitalwatermarkcanbevisibleorinvisible.Avisiblewatermarktypicallyconsistsofa第2页conspicuouslyvisiblemessageoracompanylogoindicatingtheownershipoftheimage.Ontheotherhand,aninvisiblywatermarkedimageappearsverysimilartotheoriginal.Theexistenceofaninvisiblewatermarkcanonlybedeterminedusinganappropriatewatermarkextractionordetectionalgorithm.Inthischapterwerestrictourattentiontoinvisiblewatermarks.Aninvisiblewatermarkingtechnique,ingeneral,consistsofanencodingprocessandadecodingprocess.Here,thewatermarkinsertionstepisrepresentedas:W,XEkwhereXistheoriginalimage,Wisthewatermarkinformationbeingembedded,Kistheusersinsertionkey,andErepresentsthewatermarkinsertionfunction.WeadoptthenotationthroughoutthischapterthatforanoriginalimageX,thewatermarkedvariantisrepresentedasX0.Dependingonthewaythewatermarkisinserted,anddependingonthenatureofthewatermarkingalgorithm,thedetectionorextractionmethodcantakeonverydistinctapproaches.Onemajordifferencebetweenwatermarkingtechniquesiswhetherornotthewatermarkdetectionorextractionsteprequirestheoriginalimage.Watermarkingtechniquesthatdonotrequiretheoriginalimageduringtheextractionprocessarecalledoblivious(orpublicorblind)watermarkingtechniques.Forobliviouswatermarkingtechniques,watermarkextractionworksasfollows:)(XDWKwhereXisapossiblycorruptedwatermarkedimage,Kistheextractionkey,Drepresentsthewatermarkextraction/detectionfunction,andWistheextractedwatermarkinformation.Obliviousschemesareattractiveformanyapplicationswhereitisnotfeasibletorequiretheoriginalimagetodecodeawatermark.Invisiblewatermarkingschemescanalsobeclassifiedaseitherrobustorfragile.Robustwatermarksareoftenusedtoproveownershipclaimsandsoaregenerallydesignedtowithstandcommonimageprocessingtaskssuchascompression,cropping,scaling,filtering,contrastenhancement,printing/scanning,第3页etc.,inadditiontomaliciousattacksaimedatremovingorforgingthewatermark.2.ApplicationsDigitalWatermarksarepotentiallyusefulinmanyapplications,including:(1)OwnershipassertionWatermarkscanbeusedforownershipassertion.Toassertownershipofanimage,Alicecangenerateawatermarkingsignalusingasecretprivatekey,andthenembeditintotheoriginalimage.Shecanthenmakethewatermarkedimagepubliclyavailable.Later,whenBobcontendstheownershipofanimagederivedfromthispublicimage,AlicecanproducetheunmarkedoriginalimageandalsodemonstratethepresenceofherwatermarkinBobsimage.SinceAlicesoriginalimageisunavailabletoBob,hecannotdothesame.Forsuchaschemetowork,thewatermarkhastosurviveimageprocessingoperationsaimedatmaliciousremoval.Inaddition,thewatermarkshouldbeinsertedinsuchamannerthatitcannotbeforgedasAlicewouldnotwanttobeheldaccountableforanimagethatshedoesnotown.(2)FingerprintingInapplicationswheremultimediacontentiselectronicallydistributedoveranetwork,thecontentownerwouldliketodiscourageunauthorizedduplicationanddistributionbyembeddingadistinctwatermark(orafingerprint)ineachcopyofthedata.If,atalaterpointintime,unauthorizedcopiesofthedataarefound,thentheoriginofthecopycanbedeterminedbyretrievingthefingerprint.Inthisapplicationthewatermarkneedstobeinvisibleandmustalsobeinvulnerabletodeliberateattemptstoforge,removeorinvalidate.Furthermore,andunliketheownershipassertionapplication,thewatermarkshouldberesistanttocollusion.Thatis,agroupofkuserswiththesameimagebutcontainingdifferentfingerprints,shouldnotbeabletocolludeandinvalidateanyfingerprintorcreateacopywithoutanyfingerprint.(3)Copypreventionorcontrol第4页Watermarkscanalsobeusedforcopypreventionandcontrol.Forexample,inaclosedsystemwherethemultimediacontentneedsspecialhardwareforcopyingand/orviewing,adigitalwatermarkcanbeinsertedindicatingthenumberofcopiesthatarepermitted.Everytimeacopyismadethewatermarkcanbemodifiedbythehardwareandafterapointthehardwarewouldnotcreatefurthercopiesofthedata.AnexampleofsuchasystemistheDigitalVersatileDisc(DVD).Infact,acopyprotectionmechanismthatincludesdigitalwatermarkingatitscoreiscurrentlybeingconsideredforstandardizationandsecondgenerationDVDplayersmaywellincludetheabilitytoreadwatermarksandactbasedontheirpresenceorabsence.Anotherexampleisindigitalcinema,whereinformationcanbeembeddedasawatermarkineveryframeorasequenceofframestohelpinvestigatorslocatethesceneofthepiracymorequicklyandpointoutweaknessesinsecurityinthemoviesdistribution.Theinformationcouldincludedatasuchasthenameofthetheaterandthedateandtimeofthescreening.Thetechnologywouldbemostusefulinfightingaformofpiracythatssurprisinglycommon,i.e.,whensomeoneusesacamcordertorecordthemovieasitsshowninatheater,thenduplicatesitontoopticaldisksorVHStapesfordistribution.(4)FraudandtamperdetectionWhenmultimediacontentisusedforlegalpurposes,medicalapplications,newsreporting,andcommercialtransactions,itisimportanttoensurethatthecontentwasoriginatedfromaspecificsourceandthatithadnotbeenchanged,manipulatedorfalsified.Thiscanbeachievedbyembeddingawatermarkinthedata.Subsequently,whenthephotoischecked,thewatermarkisextractedusingauniquekeyassociatedwiththesource,andtheintegrityofthedataisverifiedthroughtheintegrityoftheextractedwatermark.Thewatermarkcanalsoincludeinformationfromtheoriginalimagethatcanaidinundoinganymodificationandrecoveringtheoriginal.Clearlyawatermarkusedforauthenticationpurposesshouldnotaffectthequalityofanimageandshouldberesistanttoforgeries.Robustnessisnotcriticalasremovalofthewatermarkrendersthecontentinauthenticandhenceofnovalue.第5页(5)IDcardsecurityInformationinapassportorID(e.g.,passportnumber,personsname,etc.)canalsobeincludedinthepersonsphotothatappearsontheID.Byextractingtheembeddedinformationandcomparingittothewrittentext,theIDcardcanbeverified.Theinclusionofthewatermarkprovidesanadditionallevelofsecurityinthisapplication.Forexample,iftheIDcardisstolenandthepictureisreplacedbyaforgedcopy,thefailureinextractingthewatermarkwillinvalidatetheIDcard.Theaboverepresentafewexampleapplicationswheredigitalwatermarkscouldpotentiallybeofuse.Inadditiontherearemanyotherapplicationsinrightsmanagementandprotectionliketrackinguseofcontent,bindingcontenttospecificplayers,automaticbillingforviewingcontent,broadcastmonitoringetc.Fromthevarietyofpotentialapplicationsexemplifiedaboveitisclearthatadigitalwatermarkingtechniqueneedstosatisfyanumberofrequirements.Sincethespecificrequirementsvarywiththeapplication,watermarkingtechniquesneedtobedesignedwithinthecontextoftheentiresysteminwhichtheyaretobeemployed.Eachapplicationimposesdifferentrequirementsandwouldrequiredifferenttypesofinvisibleorvisiblewatermarkingschemesoracombinationthereof.Intheremainingsectionsofthischapterwedescribesomegeneralprinciplesandtechniquesforinvisiblewatermarking.Ouraimistogivethereaderabetterunderstandingofthebasicprinciples,inherenttrade-offs,strengths,andweakness,ofdigitalwatermarking.Wewillfocusonimagewatermarkinginourdiscussionsandexamples.Howeveraswementionedearlier,theconceptsinvolvedaregeneralinnatureandcanbeappliedtootherformsofcontentsuchasvideoandaudio.3.RelationshipwithInformationHidingandSteganographyInadditiontodigitalwatermarking,thegeneralideaofhidingsomeinformationindigitalcontenthasawiderclassofapplicationsthatgobeyondmerecopyrightprotectionandauthentication.Thetechniquesinvolvedinsuchapplicationsarecollectivelyreferredtoasinformationhiding.For第6页example,animageprintedonadocumentcouldbeannotatedbyinformationthatcouldleadanusertoitshighresolutionversionasshowninFigure4.Metadataprovidesadditionalinformationaboutanimage.Althoughmetadatacanalsobestoredinthefileheaderofadigitalimage,thisapproachhasmanylimitations.Usually,whenafileistransformedtoanotherformat(e.g.,fromTIFFtoJPEGortobmp),themetadataislost.Similarly,croppingoranyotherformofimagemanipulationdestroysthemetadata.Finally,themetadatacanonlybeattachedtoanimageaslongastheimageexistsinthedigitalformandislostoncetheimageisprinted.Informationhidingallowsthemetadatatotravelwiththeimageregardlessofthefileformatandimagestate(digitaloranalog).Metadatainformationembeddedinanimagecanservemanypurposes.Forexample,abusinesscanembedthewebsiteURLforaspecificproductinapicturethatshowsanadvertisementforthatproduct.Theuserholdsthemagazinephotoinfrontofalow-costCMOScamerathatisintegratedintoapersonalcomputer,cellphone,orapalmpilot.Thedataisextractedfromthelow-qualitypictureandisusedtotakethebrowsertothedesignatedwebsite.AnotherexampleisembeddingGPSdata(about56bits)aboutthecapturelocationofapicture.Thekeydifferencebetweenthisapplicationandwatermarkingistheabsenceofanactiveadversary.Inwatermarkingapplicationslikecopyrightprotectionandauthentication,thereisanactiveadversarythatwouldattempttoremove,invalidateorforgewatermarks.Ininformationhidingthereisnosuchactiveadversaryasthereisnovalueassociatedwiththeactofremovingtheinformationhiddeninthecontent.Nevertheless,informationhidingtechniquesneedtoberobustagainstaccidentaldistortions.Forexample,intheapplicationshowninFigure4,theinformationembeddedinthedocumentimageneedstobeextracteddespitedistortionsincurredintheprintandscanprocess.Butthesedistortionsarejustapartofaprocessandnotcausedbyanactiveadversary.Anothertopicthatisrelatedtowatermarkingissteganography(meaningcoveredwritinginGreek),whichisthescienceandartofsecretcommunication.Althoughsteganographyhasbeenstudiedaspartofcryptographyformanydecades,thefocusofsteganographyissecret第7页communication.Infact,themodernformulationoftheproblemgoesbythenameoftheprisonersproblem.HereAliceandBobaretryingtohatchanescapeplanwhileinprison.Theproblemisthatallcommunicationbetweenthemisexaminedbyawarden,Wendy,whowillplacebothoftheminsolitaryconfinementatthefirsthintofanysuspiciouscommunication.Hence,AliceandBobmusttradeseeminglyinconspicuousmessagesthatactuallycontainhiddenmessagesinvolvingtheescapelan.Therearetwoversionsoftheproblemthatareusuallydiscussedonewherethewardenispassive,andonlyobservesmessagesandtheotherwherethewardenisactiveandmodifiesmessagesinalimitedmannertoguardagainsthiddenmessages.Clearlythemostimportantissuehereisthattheverypresenceofahiddenmessagemustbeconcealed.Whereasindigitalwatermarkingitisnotclearthatagoodwatermarkingtechniqueshouldalsobesteganographic.4.WatermarkingIssuesTheimportantissuesthatariseinthestudyofdigitalwatermarkingtechniquesare:(1)Capacity:whatistheoptimumamountofdatathatcanbeembeddedinagivensignal?Whatistheoptimumwaytoembedandthenlaterextractthisinformation?(2)Robustness:Howdoweembedandretrievedatasuchthatitwouldsurvivemaliciousoraccidentalattemptsatremoval?(3)Transparency:Howdoweembeddatasuchthatitdoesnotperceptuallydegradetheunderlyingcontent?(4)Security:Howdowedeterminethattheinformationembeddedhasnotbeentampered,forgedorevenremoved?Indeed,thesequestionshavebeenthefocusofintensestudyinthepastfewyearsandsomeremarkableprogresshasalreadybeenmade.However,therearestillmorequestionsthananswersinthisrapidlyevolvingresearcharea.Perhapsakeyreasonforthisisthefactthatdigitalwatermarkingisinherentlyamulti-disciplinarytopicthatbuildsondevelopmentsindiversesubjects.Theareasthatcontributetothedevelopmentofdigitalwatermarking第8页includeattheveryleastthefollowing:(5)InformationandCommunicationTheory(6)DecisionandDetectionTheory(7)SignalProcessing(8)CryptographyandCryptographicProtocolsEachoftheseareasdealswithaparticularaspectofthedigitalwatermarkingproblem.Generallyspeaking,informationandcommunicationtheoreticmethodsdealwiththedataembedding(encoder)sideoftheproblem.Forexample,informationtheoreticmethodsareusefulinthecomputationoftheamountofdatathatcanbeembeddedinagivensignalsubjecttovariousconstraintssuchaspeakpower(squareoftheamplitude)oftheembeddeddataortheembeddinginduceddistortion.Thehostsignalcanbetreatedasacommunicationchannelandvariousoperationssuchascompression/decompression,filteringetc.canbetreatedasnoise.Usingthisframework,manyresultsfromclassicalinformationtheorycanbeandindeedhavebeensuccessfullyappliedtocomputethedataembeddingcapacityofasignal.Decisiontheoryisusedtoanalyzedata-embeddingproceduresfromthereceiver(decoder)side.Givenadata-embeddingprocedurehowdoweextractthehiddendatafromthehostsignalwhichmayhavebeensubjectedtointentionalorunintentionalattacks?Thedataextractionproceduremustbeabletoguaranteecertainamountofreliability.Whatarethechancesthattheextracteddataisindeedtheoriginalembeddeddata?Evenifthedata-embeddingalgorithmisnotintelligentorsophisticated,agooddataextractionalgorithmcanoffsetthiseffect.Inwatermarkingapplicationswheretheembeddeddataisusedforcopyrightprotection,decisiontheoryisusedtodetectthepresenceofembeddeddata.Inapplicationslikemediabridging,detectiontheoreticmethodsareneededtoextracttheembeddedinformation.Therefore,decisiontheoryplaysaveryimportantroleinthecontextofdigitalwatermarkingfordataextractionanddetection.Infact,itisshownthatinthecaseofusinginvisiblewatermarksforresolvingrightfulownership,uniquenessproblemsariseduetothedatadetectionprocess第9页irrespectiveofthedataembeddingprocess.Therefore,thereisarealandimmediateneedtodevelopreliable,efficient,androbustdetectorsfordigitalwatermarkingapplications.Avarietyofsignalprocessingalgorithmscanbeandhavebeenusedfordigitalwatermarking.Suchalgorithmsarebasedonaspectsofthehumanvisualsystem,propertiesofsignaltransforms(e.g.,Fourieranddiscretecosinetransform(DCT),noisecharacteristics,propertiesofvarioussignalprocessingattacksetc.Dependingonthenatureoftheapplicationandthecontextthesemethodscanbeimplementedattheencoder,atthedecoder,orboth.Theuserhastheflexibilitytomixandmatchfromdifferenttechniquesdependingonthealgorithmicandcomputationalconstraints.Althoughissuessuchasvisualquality,robustness,andreal-timeconstraintscanbeaccommodated,itisstillnotclearifallthedesirablepropertiesfordigitalwatermarkingdiscussedearliercanbeachievedbyanysinglealgorithm.Inmostcasesthesepropertieshaveaninherenttrade-off.Therefore,developingsignalprocessingmethodstostrikeanoptimalbalancebetweenthecompetingpropertiesofadigitalwatermarkingalgorithmisnecessary.Cryptographicissueslieatthecoreofmanyapplicationsofinformationhidingbuthaveunfortunatelyseenlittleattention.Perhapsthisisduetothefactthatmostworkindigitalwatermarkinghasbeendoneinthesignalprocessingandcommunicationscommunitywhereascryptographershavefocusedmoreonissueslikesecretcommunication(covertchannels,subliminalchannels),andcollusionresistantfingerprinting.Itisoftenassumedthatsimplyusingappropriatecryptographicprimitiveslikeencryption,time-stamps,digitalsignatures,hashfunctions,etc.wouldresultinsecureinformationhidingapplications.Webelievethisisfarfromthetruth.Infact,webelievethatthedesignofsecuredigitalwatermarkingtechniquesrequiresanintricateblendofcryptographyalongwithinformationtheoryandsignalprocessing.第10页5.ConclusionsDigitalwatermarkingisarapidlyevolvingareaofresearchanddevelopment.Weonlydiscussedthekeyproblemsinthisareaandpresentedsomeknownsolutionsinthischapter.Onekeyresearchproblemthatwestillfacetodayisthedevelopmentoftrulyrobust,transparentandsecurewatermarkingtechniquefordifferentdigitalmediaincludingimages,videoandaudio.Anotherkeyproblemisthedevelopmentofsemi-fragileauthenticationtechniques.Thesolutiontotheseproblemwillrequireapplicationofknownresultsanddevelopmentofnewresultsinthefieldsofinformationandcodingtheory,adaptivesignalprocessing,gametheory,statisticaldecisiontheoryandcryptography.Althoughalotofprogresshasalreadybeenmade,therestillremainmanyopenissuesthatneedattentionbeforethisareabecomesmature.Thischapterhasonlyprovidedasnapshotofthecurrentstate-of-the-art.Wehopethesereferenceswillbeusefulbothtoanewcomerandanadvancedresearcher.第11页中文翻译稿数字水印1.介绍互联网的出现创造了许多新在数字形式的创建和交付的内容方面的机会。数字水印的应用包括电子广告、实时视频和音频、数码存储库和库和Web发布。一个重要的问题出现在这些应用程序是所有参与者的权利的保护。已经意识到很长一段时间,目前版权法律处理数字数据是不够的。这导致对开发新副本威慑和保护机制感兴趣。这样的一个努力,已经吸引了越来越多的对基于数字水印技术的兴趣。数字水印就是将信息嵌入到数字多媒体内容的过程,这样的信息(我们称之为水印)可以提取或检测预防和控制各种目的,包括副本。数字水印已成为一个活跃的和重要的研究领域,数字水印技术的发展和商业化是被认为有必要的帮助解决所面临的一些挑战的快速扩散数字内容。如果我们假设的内容有水印的仍然是一个形象,尽管使用了大多数数字水印技术,原则上,同样适用于音频和视频数据。数字水印可以分为可见或不可见。可见水印通常由一个明显可见的消息或一个公司标志指示的所有权图像。另一方面,一个不可见水印图像似乎非常相似原始的。一个不可见水印的存在只能使用一个适当的水印提取或检测算法决定。在这里,我们限制我们的注意力为不可见水印。一个看不见的水印技术,一般来说由一个编码的过程和一个解码的过程。在这里,水印插入步骤被表示为:);(WXEK其中X是原始图像,W水印信息嵌入,K是用户的插入钥匙,和E代表水印插入功能。我们采用原始图像的符号在本章X表示为X有水印的变体。根据水印插入的方式,根据水印算法的性质,检测或提取方法可以在非常不同的方法。数字水印技术的一个主要区别：)(XDWKX在那里可能有损坏水印的图像,提取关键是k,D代表水印提取/检测函数,W是提取的水印信息,。健忘方案对于很多应用程序来说,它的吸引力是不可行的，要求原始图像解码一个水印。第12页不可见水印方案也可以归类为健壮或脆弱。健壮水印通常是用来证明所有权的声明,所以通常旨在抵御常见的图像处理任务,如压缩、剪切、缩放、滤波、对比度增强、打印/扫描,等等,除了恶意攻击旨在消除或伪造水印.2.应用数字水印是潜在有用的在许多应用程序中,包括:（1）所有权声明水印可用于所有权声明。维护一个图像的所有权,爱丽丝可以使用一个秘密私钥生成水印信号,然后嵌入到原始图像。她可以使公开有水印的图像。之后,当鲍勃认为图像的所有权派生从这个公众形象,爱丽丝可以产生没有任何标记的原始图像,也证明她在鲍勃的水印图像的存在。此外,该水印应该插入以这样一种方式,它不能被伪造的爱丽丝不想追究责任,她没有自己的形象。（2）指纹识别在应用电子分布在网络上的多媒体内容,内容所有者想阻止未经授权的复制和分布通过中嵌入不同的水印(或指纹)在每个数据的副本。在稍后的时间点,如果未经授权的拷贝的数据发现,然后复制的起源可以由检索指纹。在这个应用程序中需要对水印不可见,也必须是无懈可击的,故意伪造、删除或无效。此外,与所有权声明应用程序不同,水印应该抵抗共谋。也就是一群k用户提供相同的图像包含不同的指纹,但不能勾结和无效任何指纹或创建一个副本没有任何指纹。（3）复制预防或控制水印也可以用于预防和控制副本。举个例子,在一个封闭的系统,多媒体内容需要特殊的硬件复制和/或查看、数字水