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1、CHAPTER17EmissionSecurityThehumofeitherarmystillysounds,ThatthefixedsentinelsalmostreceiveThesecretwhispersofeachothers’watch;Fireanswersfire,andthroughtheirpalyflamesEachbattleseestheother’sumbredface.—WilliamShakespeare,KingHenryV,ActIV17.1IntroductionEmissionsecurity,
2、orEmsec,isaboutpreventingattacksusingcompromisingemanations,namelyconductedorradiatedelectromagneticsignals.Ithasmanyaspects.MilitaryorganizationsaregreatlyconcernedwithTempestdefenses,whichpreventthestrayRFemittedbycomputersandotherelectronicequipmentfrombeingpickedu
3、pbyanopponentandusedtoreconstructthedatabeingprocessed.Tempesthasrecentlybecomeanissueforelectronicvotingtoo,afteraDutchgroupfoundtheycouldtellatadistancewhichpartyavoterhadselectedonavotingmachine.Thesmartcardindustryhasbeengreatlyexercisedbypoweranalysis,inwhichacom
4、putationbeingperformedbyasmartcardsuchasadigitalsignatureisobservedbymeasuringthecurrentdrawnbytheCPUandthemeasurementsusedtoreconstructthekey.Thesethreatsarecloselyrelated,andhaveanumberofcommoncountermeasures.Researchershavealsodiscoveredattacksthatexploitstrayoptic
5、al,thermalandacousticemanationsfromvariouskindsofequipment.Suchtechniquesarealsoreferredtoassidechannelattacksastheinformationisleakingthroughachannelotherthanthosedeliberatelyengineeredforcommunication.523524Chapter17■EmissionSecurityPeopleoftenunderestimatetheimport
6、anceofEmsec.However,itseemsthattheworldsmilitaryorganizationsspentasmuchonitasoncryptographyduringthelastquarterofthetwentiethcentury.Inthecommercialworld,theuptakeofsmartcardswasmateriallysetbackinthelastfewyearsofthatcenturybytherealizationthatallthesmartcardsthenon
7、themarketwereextremelyvulnerabletosimpleattackswhichrequiredtheattackeronlytotrickthecustomerintousingaspeciallyadaptedterminalthatwouldanalyzethecurrentitdrewduringasmallnumberoftransactions.Theseattacksdidnotinvolvepenetratingthecardandthusmightleavenotrace.Oncefield
8、ed,theywereverymuchcheaperthanprobingattacks,andpotentiallyallowedlarge-scalecard-cloningattacksagainstanunsuspectingcardhol
