2012-Privacy Preserving Access Control with Authentication for securing data in clouds

2012 12th IEEE/ACM International Symposium on Cluster, Cloud and Grid Computing

PrivacyPreservingAccessControlwithAuthentication

forSecuringDatainClouds

SushmitaRuj ,MilosStojmenovic ,AmiyaNayak

SEECS,UniversityofOttawa,Canada–{sruj,anayak}@site.uottawa.ca SingidunumUniversity,Belgrade,Serbia–mstojmenovic@singidunum.ac.rs

Abstract—Inthispaper,weproposeanewprivacypreservingauthenticatedaccesscontrolschemeforsecuringdatainclouds.Intheproposedscheme,thecloudveri estheauthenticityoftheuserwithoutknowingtheuser’sidentitybeforestoringinformation.Ourschemealsohastheaddedfeatureofaccesscontrolinwhichonlyvalidusersareabletodecryptthestoredinformation.Theschemepreventsreplayattacksandsupportscreation,modi cation,andreadingdatastoredinthecloud.Moreover,ourauthenticationandaccesscontrolschemeisdecentralizedandrobust,unlikeotheraccesscontrolschemesdesignedforcloudswhicharecentralized.Thecommunication,computation,andstorageoverheadsarecomparabletocentralizedapproaches.

Keywords:Accesscontrol,Authentication,Attribute-basedsig-natures,Attribute-basedencryption,Cloudstorage.

I.INTRODUCTION

Researchincloudcomputingisreceivingalotofattentionfrombothacademicandindustrialworlds.Incloudcomputing,userscanoutsourcetheircomputationandstoragetoservers(alsocalledclouds)usingInternet.Thisfreesusersfromthehasslesofmaintainingresourceson-site.Cloudscanprovideseveraltypesofserviceslikeapplications(e.g.,GoogleApps,Microsoftonline),infrastructures(e.g.,Amazon’sEC2,Eucalyptus,Nimbus),andplatformstohelpdeveloperswriteapplications(e.g.,Amazon’sS3,WindowsAzure).

Sinceservicesareoutsourcedtoaremoteserver,securityandprivacyareofimmenseconcernincloudcomputing.Inonehand,theusershouldauthenticateitselfbeforeinitiatinganytransaction,andontheotherhand,itmustbeensuredthattheclouddoesnottamperwiththedatathatisoutsourced.Userprivacyisalsorequiredsothatthecloudorotherusersdonotknowtheidentityoftheuser.Thecloudcanholdtheuseraccountableforthedataitoutsources,andlikewise,thecloudisitselfaccountablefortheservicesitprovides.Thevalidityoftheuserwhostoresthedataisalsoveri ed.Apartfromthetechnicalsolutionstoensuresecurityandprivacy,thereisalsoaneedforlawenforcement.

Ef cientsearchisalsoanimportantconcerninclouds.Thecloudsshouldnotknowthequerybutshouldbeabletoreturntherecordsthatsatisfythequery.Thisisachievedbymeansofsearchableencryption[1],[2].Thekeywordsaresenttothecloudencrypted,andthecloudreturnstheresultwithoutknowingtheactualkeywordforthesearch.Theproblemhereisthatthedatarecordsshouldhavekeywordsassociatedwiththemtoenablethesearch.Thecorrectrecordsarereturnedonlywhensearchedwiththeexactkeywords.

Securityandprivacyprotectionincloudsarebeingexploredbymanyresearchers.Authenticationofusersusingpublickeycryptographictechniqueshasbeenstudiedin[3].Manyhomo-morphicencryptiontechniqueshavebeensuggested[4],[5]to

ensurethatthecloudisnotabletoreadthedatawhileperformingcomputationsonthem.Usinghomomorphicencryption,thecloudreceivesciphertextofthedataandperformscomputationsontheciphertextandreturnstheencodedvalueoftheresult.Theuserisabletodecodetheresult,buttheclouddoesnotknowwhatdataithasoperatedon.Insuchcircumstances,itmustbepossiblefortheusertoverifythatthecloudreturnscorrectresults.Theothercloselyrelatedproblemisthatofcodeobfuscation[6],inwhichtheusersendsthecodeinanencodedform,andthecloudcanexecutethecodeandreturnstheresultwithoutknowingtheactualcode.

Accountabilityofcloudsisaverychallengingtaskandinvolvestechnicalissuesandlawenforcement.Neithercloudsnorusersshoulddenyanyoperationsperformedorrequested.Itisimportanttohavelogofthetransactionsperformed;however,itisanimportantconcerntodecidehowmuchofinformationtokeepinthelog.AccountabilityhasbeenaddressedinTrustCloud[7].Letusnowconsiderthefollowingsituation.SupposeaLawstudent,Alice,wantstosendaseriesofreportsaboutsomemalpracticesbyauthoritiesofUniversityXtoalltheprofessorsofUniversityX,Researchchairsofuniversitiesinthecountry,andstudentsbelongingtoLawdepartmentinalluniversitiesintheprovince.Shewantstoremainanonymouswhilepublishingallevidenceofmalpractice.Shestorestheinformationinthecloud.Accesscontrolisimportantinsuchcase,sothatonlyauthorizeduserscanaccessthedata.Itisalsoimportanttoverifythattheinformationcomesfromareliablesource.Theproblemsofaccesscontrol,authentication,andprivacyprotectionshouldbesolvedsimultaneously.Weaddressthisprobleminentiretyinthispaper.Accesscontrolincloudsisgainingattentionbecauseitisimportantthatonlyauthorizedusershaveaccesstovalidservice.Ahugeamountofinformationisbeingstoredinthecloud,andmuchofthisissensitiveinformation.Careshouldbetakentoensureaccesscontrolofthissensitiveinformationwhichcanoftenberelatedtohealth,importantdocuments(asinGoogleDocsorDropbox)orevenpersonalinformation(asinsocialnetworking).Therearebroadlythreetypesofaccesscontrol:UserBasedAccessControl(UBAC),RoleBasedAccessControl(RBAC),andAttributeBasedAccessControl(ABAC).InUBAC,theaccesscontrollist(ACL)containsthelistofuserswhoareauthorizedtoaccessdata.Thisisnotfeasibleincloudswheretherearemanyusers.InRBAC(introducedby[8]),usersareclassi edbasedontheirindividualroles.Datacanbeaccessedbyuserswhohavematchingroles.Therolesarede nedbythesystem.Forexample,onlyfacultymembersandseniorsecretariesmighthaveaccesstodatabutnotthejuniorsecretaries.TheABACismoreextendedinscope,inwhichusersaregivenattributes,andthedatahas