How fingerprint scanners work — Optical, capacitive, and ...

Just like smartphone cameras, these sensors have a finite resolution. The higher the resolution, the finer details the sensor can discern about ... BestdailydealsLinksonAndroidAuthoritymayearnusacommission. Learnmore. FeaturesHowfingerprintscannerswork:Optical,capacitive,andultrasonicexplainedFingerprintscannersareanessentialfeatureinthesmartphonemarket.ByRobertTriggs•April8,2022RobertTriggs/AndroidAuthorityFingerprintscannersaren’tjustreservedfortheverytop-tiersmartphonesanymore.Evenmanybudgetphonessportthetechthesedays,whichisacornerstoneofappsecurity.Thetechnologyhasalsomovedonalotfromitsearlyiterations,becomingfasterandmoreaccurateatcapturingyourfingerprint.Withallthatinmind,let’stakealookathowthelatestfingerprintscannersworkandwhatthedifferencesare. Staysecure:15bestantivirusappsandbestanti-malwareappsforAndroid Opticalscanners Opticalfingerprintscannersaretheoldestmethodofcapturingandcomparingfingerprints.Asthenamesuggests,thistechniquereliesoncapturinganopticalimage—essentiallyaphotograph.Itthenusesalgorithmstodetectuniquepatternsonthesurface,suchasridgesormarks,byanalyzingthelightestanddarkestareasoftheimage.Justlikesmartphonecameras,thesesensorshaveafiniteresolution.Thehighertheresolution,thefinerdetailsthesensorcandiscernaboutyourfinger,increasingthelevelofsecurity.However,thesesensorscapturemuchhighercontrastimagesthanaregularcamera.Opticalscannerstypicallyhaveaveryhighnumberofdiodesperinchtocapturethesedetailsupclose.Ofcourse,it’sverydarkwhenyourfingerisplacedoverthescanner.Thescanners,therefore,incorporatearraysofLEDsorevenyourphone’sdisplayasaflashtolightupthepicturecomescantime.Themajordrawbackwithopticalscannersisthattheyaren’tdifficulttofool.Asthetechnologyisonlycapturinga2Dpicture,prostheticsandevenpicturesofgoodqualitycanbeusedtofoolthisparticulardesign.Onitsown,thistypeofscannerreallyisn’tsecureenoughtoentrustitwithyourmostsensitivedetails.Assuch,theindustryhasmovedontomoresecurehybridsolutions.Withanincreasingdemandfortoughersecurity,smartphoneshaveunanimouslyadoptedsuperiorcapacitiveandoptical-capacitivehybridscanners.Thesescannersuseopticalfingerprintdata,combinedwithcapacitivesensingtodetectarealfinger.Thefallingcostoftechnologyhasmadethesealternativesviableformid-rangeproductstoo.Withthemovetowardsbezel-lessdisplays,smalleropticalmodulesaremakingmakeacomeback.Theycanbeembeddedunderneaththedisplayglassandonlyrequireasmallareafootprint.Somemodelsonthemarketcanoperatesuccessfullyunder1mmofglassandwithwetfingers—somethingthatmesseswithcapacitivealternatives.Hybridopticalscannersareheretostay. Capacitivescanners Anothercommonfingerprintscannertypeusedtodayisthecapacitivescanner.You’llfindthistypeofscanneronthefrontandbackofsmartphonesandevenusedaspartofcutting-edgein-displayvariants.Capacitivescannersgrewtoprominencebecauseoftheiradditionalsecuritybenefits.Againthenamegivesawaythecorecomponent—thecapacitor.Insteadofcreatingatraditionalimageofafingerprint,capacitivefingerprintscannersusearraysoftinycapacitorcircuitstocollectdata.Ascapacitorsstoreelectricalcharge,connectingthemuptoconductiveplatesonthesurfaceofthescannerallowsthemtobeusedtotrackthedetailsofafingerprint.Thestoredchargewillbechangedslightlywhenafinger’sridgeisplacedovertheconductiveplates.Conversely,anairgapwillleavethechargeatthecapacitorrelativelyunchanged.Anop-ampintegratorcircuitisusedtotrackthesechanges,whichcanthenberecordedbyananalog-to-digitalconverter. Thetheoryandarchitecturebehindacapacitivefingerprintscanningchip. SlideshareOncecaptured,thisdigitaldataisanalyzedtolookfordistinctiveanduniquefingerprintattributes.Theycanthenbesavedforcomparisonatalaterdate.Whatisparticularlysmartaboutthisdesignisthatitismuchtoughertofoolthananopticalscanner.Theresultscan’tbereplicatedwithanimage.Additionally,theyareincrediblytoughtofoolwithsomesortofprosthetic,asdifferentmaterialswillrecordslightlydifferentchangesinchargeatthecapacitor.Theonlyrealsecurityriskscomefromeitherhardwareorsoftwarehacking.Creatingalargeenougharrayofthesecapacitors,typicallyhundredsifnotthousandsinasinglescanner,allowsforahighlydetailedimageoftheridgesandvalleysofafingerprinttobecreatedfromnothingmorethanelectricalsignals.Justliketheopticalscanner,morecapacitorsresultinahigherresolutionscanner.Thisincreasesthelevelofsecurity,uptoacertainpoint.Nevertheless,highdensitycostsalotmoretoproduce. Seealso:ThebestsecurityappsforAndroidthataren’tantivirusappsDuetothelargernumberofcomponentsinthedetectioncircuit,capacitivescannershadpreviouslybeenquitepricey.Someearlyimplementationsattemptedtocutthenumberofcapacitorsneededbyusing“swipe”scanners.Theywouldcollectdatafromasmallernumberofcapacitorcomponentsbyquicklyrefreshingtheresultsasafingerispulledoverthesensor.Asmanyconsumerscomplainedatthetime,thismethodwasveryfinickyandoftenrequiredseveralattemptstoscantheresultcorrectly.Fortunately,thesedays,thesimplepressandholddesignisthedefaultsetup.Youcandomorethanjustreadfingerprintswiththesescanners,however.Newermodelssportgestureandswipefunctionalitytoo.Thesecanbeusedassoftbuttonsupporttoactasnavigationkeys,forcesensingcapabilities,orasawaytointeractwithotherUIelements.However,premium-tiersmartphoneshavemovedontoin-displaytechnologies.DavidImel/AndroidAuthorityUltrasonicscanners Thelatestfingerprintscanningtechnologytoenterthesmartphonespaceistheultrasonicsensor.Itwasfirstannouncedinside2016’sLeMaxProsmartphone.QualcommanditsSenseIDtechnologyareamajorpartofthedesign.Infact,QualcommisnowonitssecondgenerationofUltrasonicfingerprintscanningtechnology(technicallyitsthirdproduct).Itpromisesabiggerreadingareaandfasterprocessingspeeds.Toactuallycapturethedetailsofafingerprint,thehardwareconsistsofbothanultrasonictransmitterandareceiver.Anultrasonicpulseistransmittedagainstthefingerthatisplacedoverthescanner.Someofthispulseisabsorbedandsomeofitisbouncedbacktothesensor,dependingupontheridges,pores,andotherdetailsthatareuniquetoeachfingerprint. Thereisn’tamicrophonelisteningoutforthesereturningsignals.Instead,asensorthatcandetectmechanicalstressisusedtocalculatetheintensityofthereturningultrasonicpulseatdifferentpointsonthescanner.Scanningforlongerperiodsoftimeallowsforadditionaldepthdatatobecaptured.Thisresultsinadetailed3Dreproductionofthescannedfingerprint.The3Dnatureofthiscapturetechniquemakesitanevenmoresecurealternativetocapacitivescanners.Qualcomm3Dultrasonicin-displayfingerprintsensorhassubsequentlybeenadoptedinsideSamsung’sflagshipsincludingthelatestGalaxyS22.Samsungpointsoutthatthisnewscanneris77%largerand50%fasterthanthepreviousgenerationproduct.Thedrawbackoftheultrasonicisthatit’snotassnappyasotherscannersyet.Thisispartlyduetothereasonsmentionedabove.However,Qualcommhasaddressedthiswithsomewhatitssecond-generationtechnology.Ultrasonictechalsodoesn’tplaynicelywithsomescreenprotectors,particularlythethickerones.Theycanlimittheabilityofthescannertoreadfingerprintscorrectly.Ontheplusside,bezelsarethinnerthaneverduetobeingabletohidethescannerunderthedisplay.Awordonin-displayscanners Ultrasonicfingerprintscannersaren’ttheonlyoptionifyouwanttohidethesensorinthedisplay.Optical-capacitivefingerprintscannersarebeingusedforthispurposetoo.Theindustryiscurrentlysplitbetweenthesetwo.However,you’llseldomfindultrasonicscannersatthemoreaffordableendofthemarket.Optical-capacitivescannersaddresssomeprevioussecurityissueswithopticaldesigns.Theycombinethe“realtouch”requirementsofcapacitivescannerswiththespeedandenergyefficiencyofopticaldesigns.Thistechnologyisembeddedbyinsertingasensorunderthedisplay.ItdetectslightreflectedbyafingerprintbackthroughthegapsintheOLEDdisplay.Thisrequiressomeworktointegratewiththedisplay,butitworksquitewell.You’llfindvariousin-displayopticalfingerprinttechnologiesinbothaffordableandpremiumtierhandsets,includingSamsung’sGalaxyAseries.Ultrasonicscanners,bycomparison,arealittleeasiertoimplementandadjusttheirplacementtosuitanyhandset.Thetiny0.2mmthicksensorsitsbehindthescreen,passingitsultrasonicwavesthroughthedisplaytoyourfingertip.Whilethisisgreatfordevelopment,ithasledtoafewsecurityproblemsofitsown.Samsunghadtoissuepatchestoitsflagshipsmartphonestoaddressissuesthatallowedalmostanyfingerprinttounlockthephoneswhenusingascreenprotector.Bothtechnologieshavetheirprosandconsandwilllikelyremainviablechoicesforin-displayfingerprintscannersforyearstocome.However,ultrasonicscannersmaytakeawhilelongertomaketheirwaytomoreaffordablepricepoints. Cryptography,andsecureprocessing Whilemostfingerprintscannersarebasedonverysimilarhardwareprinciples,additionalcomponentsandsoftwarecanalsoplayamajorpartindifferentiatinghowproductsperformandwhatfeaturesareavailabletoconsumers.AccompanyingthephysicalscannerisadedicatedIC.Itinterpretsthescanneddataandtransmitsitinausefulformtoyoursmartphone’smainprocessor.Differentmanufacturersuseslightlydifferentalgorithmstoidentifykeyfingerprintcharacteristics,whichcanvaryinspeedandaccuracy.Typicallythesealgorithmslookforwhereridgesandlinesend,orwherearidgesplitsintwo.Collectively,theseandotherdistinctivefeaturesarecalledminutiae.Ifascannedfingerprintmatchesseveraloftheseminutiaethenitwillbeconsideredamatch.Ratherthancomparingthewholefingerprinteachtime,comparingminutiaereducestheamountofprocessingpowerrequiredtoidentifyeachfingerprint.Additionally,ithelpsavoiderrorsifthescannedfingerprintissmudged.Italsoallowsthefingertoplacedoff-centerorbeidentifiedwithonlyapartialprint.ARMTrustZoneisusedtokeepbiometricandcryptographicdatasecurefromtheRichOS.Ofcourse,thisinformationneedstobekeptsecureonyourdeviceandsavedwellawayfromcodethatcouldcompromiseit.Ratherthanuploadingthisuserdataonline,ARMprocessorscankeepthisinformationsecurelyonthephysicalchipusingitsTrustedExecutionEnvironment(TEE)basedTrustZonetechnology.Thissecureareaisalsousedforothercryptographicprocessesandtocommunicatedirectlywithsecurehardwareplatforms,suchasafingerprintscanner.Approvedpiecesofone’spersonalinformation,suchasapasswordkey,canonlybeaccessedbyapplicationsusingtheTEEclientAPIs.HowFIDOloginworkswithoutsendinganypersonallyidentifiableinformation.Qualcomm’stakeonthisisbuiltintoitsSecureMSMarchitectureandSecureProcessingUnit(SPU).Apple,ontheotherhand,talksthisupasthe“SecureEnclave”.Eitherway,it’sbasedonthesameprincipleofkeepingthissecuredataonaseparatepartoftheprocessor.There,itcannotbeaccessedbyappsoperatingintheregularoperatingsystemenvironment.TheFIDO(FastIDentityOnline)Alliancehasdevelopedstrongcryptographicprotocolsthatusetheseprotectedhardwarezonestoenablepassword-lessauthenticationhandshakesbetweenhardwareandservices.So,youcanlogintoawebsiteoronlineshopusingyourfingerprintwithoutyouruniquedataeverleavingyoursmartphone.Thisisaccomplishedbypassingdigitalkeysratherthanbiometricdatatoservers. Readmore:Thebestphoneswithin-displayfingerprintscannersFingerprintscannershavebecomeaverysecurealternativetorememberingcountlessusernames,pins,andpasswordsstoredonourphones.Theirincreasingspeed,highlevelofsecurity,andhiddenin-displaydesignsensurethatthey’llbestickingarounddespitethegrowingadoptionofexpensivefacialunlockingtechnology.Thewidespreadroll-outofsecuremobilepaymentsystemsmeansthatthesescannersaresuretoremainacrucialsecuritytoolinthefuture. FeaturesFingerprintscannerComments