安卓的机制与安全性毕业论文外文翻译.doc

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1、附录A 外文翻译-原文部分Android security mechanismThenextgenerationofopenoperatingsystemswontbeondesktopsormainframesbutonthesmallmobiledeviceswecarryeveryday.Theopennessofthesenewenvironmentswillleadtonewapplicationsandmarketsandwillenablegreaterintegrationwithexistingonlineservices.However,astheimportanceoft

2、hedataandservicesourcellphonessupportincreases,sotoodotheopportunitiesforvulnerability.Itsessentialthatthisnextgenerationofplatformsprovidesacomprehensiveandusablesecurityinfrastructure.DevelopedbytheOpenHandsetAlliance(visiblyledbyGoogle),Androidisawidelyanticipatedopensourceoperatingsystemformobil

3、edevicesthatprovidesabaseoperatingsystem,anapplicationmiddlewarelayer,aJavasoftwaredevelopmentkit(SDK),andacollectionofsystemapplications.AlthoughtheAndroidSDKhasbeenavailablesincelate2007,thefirstpubliclyavailableAndroidready“G1”phonedebutedinlateOctober2008.Sincethen,Androidsgrowthhasbeenphenomena

4、l:T-MobilesG1manufacturerHTCestimatesshipmentvolumesofmorethan1millionphonesbytheendof2008,andindustryinsidersexpectpublicadoptiontoincreasesteeplyin2009.Manyothercellphoneprovidershaveeitherpromisedorplantosupportitinthenearfuture.AlargecommunityofdevelopershasorganizedaroundAndroid,andmanynewprodu

5、ctsandapplicationsarenowavailableforit.OneofAndroidschiefsellingpointsisthatitletsdevelopersseamlesslyextendonlineservicestophones.Themostvisibleexampleofthisfeatureis,unsurprisingly,thetightintegrationofGooglesGmail,Calendar,andContactsWebapplicationswithsystemutilities.Androiduserssimplysupplyause

6、rnameandpassword,andtheirphonesautomaticallysynchronizewithGoogleservices.Othervendorsarerapidlyadaptingtheirexistinginstantmessaging,socialnetworks,andgamingservicestoAndroid,andmanyenterprisesarelookingforwaystointegratetheirowninternaloperations(suchasinventorymanagement,purchasing,receiving,ands

7、oforth)intoitaswell.Traditionaldesktopandserveroperatingsystemshavestruggledtosecurelyintegratesuchpersonalandbusinessapplicationsandservicesonasingleplatform.AlthoughdoingsoonamobileplatformsuchasAndroidremainsnontrivial,manyresearchershopeitprovidesacleanslatedevoidofthecomplicationsthatlegacysoft

8、warecancause.Androiddoesntofficiallysupportapplicationsdevelopedforotherplatforms:applicationsexecuteontopofaJavamiddlewarelayerrunningonanembeddedLinuxkernel,sodeveloperswishingtoporttheirapplicationtoAndroidmustuseitscustomuserinterfaceenvironment.Additionally,Androidrestrictsapplicationinteractio

9、ntoitsspecialAPIsbyrunningeachapplicationasitsownuseridentity.Althoughthiscontrolledinteractionhasseveralbeneficialsecurityfeatures,ourexperiencesdevelopingAndroidapplicationshaverevealedthatdesigningsecureapplicationsisntalwaysstraightforward.Androidusesasimplepermissionlabelassignmentmodeltorestri

10、ctaccesstoresourcesandotherapplications,butforreasonsofnecessityandconvenience,itsdesignershaveaddedseveralpotentiallyconfusingrefinementsasthesystemhasevolved.ThisarticleattemptstounmaskthecomplexityofAndroidsecurityandnotesomepossibledevelopmentpitfallsthatoccurwhendefininganapplicationssecurity.W

11、econcludebyattemptingtodrawsomelessonsandidentifyopportunitiesforfutureenhancementsthatshouldaidinclarityandcorrectness.AndroidApplicationsTheAndroidapplicationframeworkforcesastructureondevelopers.Itdoesnthaveamain()functionorsingleentrypointforexecutioninstead,developersmustdesignapplicationsinter

12、msofcomponents.ExampleApplicationWedevelopedapairofapplicationstohelpdescribehowAndroidapplicationsoperate.InterestedreaderscandownloadthesourcecodefromourWebsite(http:/siis.cse.psu.edu/android_sec_tutorial.html).Letsconsideralocation-sensitivesocialnetworkingapplicationformobilephonesinwhichusersca

13、ndiscovertheirfriendslocations.Wesplitthefunctionalityintotwoapplications:onefortrackingfriendsandoneforviewingthem.AsFigure1shows,theFriendTrackerapplicationconsistsofcomponentsspecifictotrackingfriendlocations(forexample,viaaWebservice),storinggeographiccoordinates,andsharingthosecoordinateswithot

14、herapplications.TheuserthenusestheFriendViewerapplicationtoretrievethestoredgeographiccoordinatesandviewfriendsonamap.Bothapplicationscontainmultiplecomponentsforperformingtheirrespectivetasks;thecomponentsthemselvesareclassifiedbytheircomponenttypes.AnAndroiddeveloperchoosesfrompredefinedcomponentt

15、ypesdependingonthecomponentspurpose(suchasinterfacingwithauserorstoringdata).ComponentTypesAndroiddefinesfourcomponenttypes:Activitycomponentsdefineanapplicationsuserinterface.Typically,anapplicationdeveloperdefinesoneactivityper“screen.”Activitiesstarteachother,possiblypassingandreturningvalues.Onl

16、yoneactivityonthesystemhaskeyboardandprocessingfocusatatime;allothersaresuspended.Servicecomponentsperformbackgroundprocessing.Whenanactivityneedstoperformsomeoperationthatmustcontinueaftertheuserinterfacedisappears(suchasdownloadafileorplaymusic),itcommonlystartsaservicespecificallydesignedforthata

17、ction.Thedevelopercanalsouseservicesasapplication-specificdaemons,possiblystartingonboot.ServicesoftendefineaninterfaceforRemoteProcedureCall(RPC)thatothersystemcomponentscanusetosendcommandsandretrievedata,aswellasregistercallbacks.Contentprovidercomponentsstoreandsharedatausingarelationaldatabasei

18、nterface.Eachcontentproviderhasanassociated“authority”describingthecontentitcontains.OthercomponentsusetheauthoritynameasahandletoperformSQLqueries(suchasSELECT,INSERT,orDELETE)toreadandwritecontent.Althoughcontentproviderstypicallystorevaluesindatabaserecords,dataretrievalisimplementationspecificfo

19、rexample,filesarealsosharedthroughcontentproviderinterfaces.Broadcastreceivercomponentsactasmailboxesformessagesfromotherapplications.Commonly,applicationcodebroadcastsmessagestoanimplicitdestination.Broadcastreceiversthussubscribetosuchdestinationstoreceivethemessagessenttoit.Applicationcodecanalso

20、addressabroadcastreceiverexplicitlybyincludingthenamespaceassignedtoitscontainingapplication.Figure1showstheFriendTrackerandFriendViewerapplicationscontainingthedifferentcomponenttypes.Thedeveloperspecifiescomponentsusingamanifestfile.Therearenorestrictionsonthenumberofcomponentsanapplicationdefines

21、foreachtype,butasaconvention,onecomponenthasthesamenameastheapplication.Frequently,thisisanactivity,asintheFriendViewerapplication.Thisactivityusuallyindicatestheprimaryactivitythatthesystemapplicationlauncherusestostarttheuserinterface;however,thespecificactivitychosenonlaunchismarkedbymetainformat

22、ioninthemanifest.IntheFriendTrackerapplication,forexample,theFriendTrackerControlactivityismarkedasthemainuserinterfaceentrypoint.Inthiscase,wereservedthename“FriendTracker”fortheservicecomponentperformingthecoreapplicationlogic.TheFriendTrackerapplicationcontainseachofthefourcomponenttypes.TheFrien

23、dTrackerservicepollsanexternalservicetodiscoverfriendslocations.Inourexamplecode,wegeneratelocationsrandomly,butextendingthecomponenttointerfacewithaWebserviceisstraightforward.TheFriendProvidercontentprovidermaintainsthemostrecentgeographiccoordinatesforfriends,theFriendTrackerControlactivitydefine

24、sauserinterfaceforstartingandstoppingthetrackingfunctionality,andtheBootReceiverbroadcastreceiverobtainsanotificationfromthesystemonceitboots(theapplicationusesthistoautomaticallystarttheFriendTrackerservice).TheFriendViewerapplicationisprimarilyconcernedwithshowinginformationaboutfriendslocations.T

25、heFriendVieweractivitylistsallfriendsandtheirgeographiccoordinates,andtheFriendMapactivitydisplaysthemonamap.TheFriendReceiverbroadcastreceiverwaitsforFriendTrackerControlactivity,forinstance,canstartandstoptheFriendTrackerservicethatrunsinthebackground.Thebindactionestablishesaconnectionbetweencomp

26、onents,allowingtheinitiatortoexecuteRPCsdefinedbytheservice.Inourexample,FriendTrackerbindstothelocationmanagerinthesystemserver.Oncebound,FriendTrackerinvokesmethodstoregisteracallbackthatprovidesupdatesonthephoneslocation.Notethatifaserviceiscurrentlybound,anexplicit“stop”actionwontterminatetheser

27、viceuntilallboundconnectionsarereleased.Broadcastreceiverandcontentprovidercomponentshaveuniqueformsofinteraction.ICCtargetedatabroadcastreceiveroccursasanintentsent(broadcast)eitherexplicitlytothecomponentor,morecommonly,toanactionstringthecomponentsubscribesto.Forexample,FriendReceiversubscribesto

28、thedeveloper-defined“FRIEND_NEAR”actionstring.FriendTrackerbroadcastsanintenttothisactionstringwhenitdeterminesthatthephoneisnearafriend;thesystemthenstartsFriendReceiveranddisplaysamessagetotheuser.Contentprovidersdontuseintentsrather,theyreaddressedviaanauthoritystringembeddedinaspecialcontentURIo

29、ftheformcontent:/.Here,indicatesatableinthecontentprovider,andoptionallyspecifiesarecordinthattable.ComponentsusethisURItoperformaSQLqueryonacontentprovider,optionallyincludingWHEREconditionsviathequeryAPI.SecurityEnforcementAsFigure3shows,Androidprotectsapplicationsanddatathroughacombinationoftwoen

30、forcementmechanisms,oneatthesystemlevelandtheotherattheICClevel.ICCmediationdefinesthecoresecurityframeworkandisthisarticlesfocus,butitbuildsontheguaranteesprovidedbytheunderlyingLinuxsystem.Inthegeneralcase,eachapplicationrunsasauniqueuseridentity,whichletsAndroidlimitthepotentialdamageofprogrammin

31、gflaws.Forexample,theWebbrowservulnerabilitydiscoveredrecentlyaftertheofficialreleaseofT-MobileG1phonesonlyaffectedtheWebbrowseritself(Becauseofthisdesignchoice,theexploitcouldntaffectotherapplicationsorthesystem.AsimilarvulnerabilityinApplesiPhonegavewaytothefirst“jailbreaking”technique,whichletusersreplacepartsoftheunderlyingsystem,butwouldalsohaveenabledanetwork-basedadversarytoexploitthisflaw(http:/