Securing Wireless Communications at the Physical Layer

401 Pages·2010·7.926 MB·English

by  Zang Li, Roy Yates, Wade Trappe (auth.), Ruoheng Liu, Wade Trappe (eds.)

Securing Wireless Communications
at the Physical Layer
Ruoheng Liu · Wade Trappe
Editors
Securing Wireless
Communications at the
Physical Layer
~
Springer
Editors
RuohengLiu Dr.WadeTrappe
PrincetonUniversity RutgersUniversity
DepartmentofElectricalEngineering TechnologyCentreofNewJersey
OldenStreet WirelessInformation
Princeton,NJ08544 671Route1South
USA NorthBrunswick,NJ08902
[email protected] USA
[email protected]
ISBN978-1-4419-1384-5 e-ISBN978-1-4419-1385-2
DOI10.1007/978-1-4419-1385-2
SpringerNewYorkDordrechtHeidelbergLondon
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(cid:2)c SpringerScience+BusinessMedia,LLC2010
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ToOurFamilies
Preface
Securingcommunicationsisachallengingtask.Afirstattemptatsecurityinvolves
learningbasiccryptography,andapplyingencryptionalgorithmstomakemessages
unintelligibletoadversaries. However, rarelyisthetaskofsecuringamessageex-
changesosimple.Whenonestepsbackandcontemplateshowtosecuretheexchange
of communications, one realizes that the challenge is fundamentally one of build-
ing a complete solution. For example, one must ensure that all entities involved
haveproperandauthenticatedcryptographicmaterial, oronemustensurethatone
verifiablyknowstowhomoneiscommunicating, oronemustunderstandhowthe
communicationprocesstakesplacesoastomakecertaintherearenovulnerabilities
introducedbythecommunicationprocessitself.
Thislastissue,namelythatsecuritymethodsareoftenbuiltwithoutconsideration
to how communication takes place, represents a fundamental gap where much of
modernsecurityresearchhasfallenshort.Thesecurityliteratureisfilledwithamass
ofarticlesoncryptographicprimitivesand,althoughtherearestillmanytheoretical
hurdlestobeovercomebythecryptographiccommunity,mostoftheseshortcomings
areacademicandtherearenownumeroustextbooksoncryptographythatcanprovide
thebasicintroductionneededtoemploycryptographicprimitives.Ontheothersideof
thecoin,thesecurityliteratureisalsofilledwithamassofarticlesdevotedtobuilding
secure protocols and, similarly, there are now numerous textbooks on computer
securitythatprovidetheinstructionneededtodesignsecureprotocols.Unfortunately,
theissueofhowcommunicationtakesplaceor,morespecifically,whetherthereare
anyspecificissuesthatmightariseorbecircumventedbecausemessageexchanges
aretakingplaceononemediumversusanother(e.g.,wirelesscommunicationversus
wiredcommunication),isgenerallyneglected.
Infact,althoughthelayeredapproachtocommunicationsystemdesign,ascorre-
spondstothegeneralOpenSystemsInterconnection(OSI)referencemodel,isoften
referredtointhedesignofnetworksecurityprotocols,theresultingprotocolstend
tobelayer-specificandignorethemostfundamentalofcommunicationlayers—the
physicallayer,wherebydevicescommunicatethroughtheencodingandmodulation
of information into waveforms. This is truly a sad situation, as it means that the
approachestakentosecuremoderncommunicationsystemsareincompleteand,as
vii
viii Preface
isoftenchantedasamantrainthesecuritycircles,weshouldbeconcernedbecause
“asystemisonlyasstrongastheweakestlink.”
Inresponsetothisapparentshortcoming,thisanthologypresentsacollectionof
chaptersdevotedtorecentresearchresultsexaminingsecurityissuesatthephysical
layer. Inparticular, alloftheauthorsamassedinthiscollectiontaketheviewpoint
thatthephysicallayerofwirelesscommunicationsshouldbeconsideredasunique
and different from the physical layer of other communication systems, and thus
the challenges of securing the physical layer should take into account the special
properties of the wireless medium. Throughout this book, a common theme that
frequently emerges is that, in the rich multipath environment typical of wireless
scenarios, the channel response of the medium along any transmit-receive path is
frequency-selective (or in the time domain, dispersive) in a way that is location-
specific (implying that channel responses decorrelate rapidly from one transmit-
receivepathtoanotherifthepathsareseparatedbytheorderofanRFwavelength).
Theseuniquespace,time,andfrequencycharacteristicsofthewirelessphysicallayer
serveasapowerfulbasisforbuildingnewsecurityservicesatthephysicallayer.
The chapters that we have assembled are contributions from a broad variety of
researchgroupsexaminingsecurityissuesatthephysicallayerofwirelesssystems.
Inselectingthecontributions,wehavesoughttocoveraspectrumofsecurityissues
(ranging from confidentiality to authentication to trustworthiness), as well as both
theoretical and practical aspects of securing the physical layer.As such, the chap-
ters in this book have been loosely organized thematically. We start by examining
the issue of confidentiality at the physical layer. Confidentiality typically involves
algorithms, like ciphers, and is concerned with the guarantee that information ex-
change is only able decipherable by legitimate entities. In the context of physical
layersecurity,wearemoreconcernedwithmechanismsthatusethewirelessmedium
to support the confidential exchange of messages. Typically, though, the resulting
mechanismsoperateatcommunicationratesthataremuchlowerthantheirconven-
tionalnon-secret counterparts, andthusphysicallayerconfidentialitymechanisms
shouldbeusedinsupportofconventionalconfidentialitymechanisms.Forexample,
one might use physical layer confidentiality mechanisms to secretly exchange or
establishconventionalcryptographickeys.
Confidentiality mechanisms at the physical layer may be further decomposed
into methods that secretly disseminate information using the properties of the
wireless medium and methods that extract secret information from the wireless
medium.Wehavearrangedtheconfidentialitychaptersbyfirstexaminingtheissue
of disseminating information secretly. Most of these chapters explore the funda-
mentaltheoreticalaspectsrelatedtosecrecydissemination,andseveralfundamental
observationsemerge.First,thefadingprocessexperiencedintypicalwirelesscom-
municationscenariosisveryspecialandcanservetoenhancetheabilitytosecretly
communicatewhencomparedtolessharshcommunicationscenarios. Second, the
broadcastnatureofthewirelessmediumallowsforonetointroduceinterferenceinto
the medium that can harm an adversary’s ability to eavesdrop while strengthening
theabilityfortwolegitimateentitiestocommunicate.Inallcases,knowledgeofthe
channelstateisimportanttotheabilitytocommunicate,andthusunderstandingthe
Preface ix
propertiesofsecretcommunicationwhenthereisincompleteorinaccuratechannel
informationisimportant.Movingawayfromthefoundationalinformation-theoretic
aspectsofsecrecydissemination,aretwochaptersthataredevotedtoexaminingthe
designofspecificcodingschemesandwhichserveasthefirststeptowardsrealistic
implementationsofsecrecydisseminationmethods.
Thesecondsetofconfidentialitychaptersseektousetheuniquespace,timeand
frequency properties of the wireless channel as the source of shared, secret infor-
mationbetweenatransmitterandreceiver.Ifthisshared,secretinformationcanbe
minedfromthewirelesschannel,thenitcanserveasthebasisforestablishingsecret
keys.Secrecyextractiontechniquesareaparticularlypromisingdirectionforusing
the physical layer to enhance security as the basic step needed to support secrecy
extraction,namelytheprobingofthewirelessmediuminordertoobtainachannel
estimate,isalsoafundamentalsteptogeneralcommunication,i.e.,channelestima-
tionisalreadyperformedinthephysicallayerofmostwirelesssystems.Although
thechaptersdevotedtosecrecyextractioninvolvesignificanttheoreticalaspects,they
alsorepresentsomeofthemostsolidevidenceinsupportofreal-worlddeployment
of physical layer security techniques. Many of the chapters include experimental
evidence and, in one case, a real-time implementation, of the validity of physical
layersecuritymechanisms.
Nextweturntotheproblemofauthentication.Authenticationtypicallyinvolves
providing assurance that entities are who they claim to be, or that messages come
from where they claim to originate.At the physical layer, the notion of identity is
different. In this context, we are not as worried with who someone is, but rather
with being able to distinguish between different transmitters. In the general wire-
less authentication problem, we are concerned with an active adversary injecting
communicationsintothemediumandclaimingthatthesetransmissionscomefrom
alegitimatewirelessdevice. Interestingly, therearemanysituationswherecrypto-
graphictechniquesforauthenticationarenoteasytoemploy,andthusitisdesirable
for an entity to differentiate between signals coming from a legitimate entity and
thosecomingfromanillegitimateentity.Physicallayerauthenticationmethodsare
anaturalcomplementtosecrecyextractiontechniquesas,inbothcases,thecharac-
terizationofthewirelesschannelservesasthefundamentalbuildingblock.Whereas
for secrecy extraction the channel estimate serves as the secret information that is
usedtoestablishakey,forphysicallayerauthenticationthechannelestimateserves
astheauthenticatortodistinguishbetweentransmittersandreceivers.Aninteresting
challengethatarisesinphysicallayerauthenticationistheneedtomaintaintheau-
thenticatorwhentheenvironmentisdynamicandentitiesaremovingaround. Our
twochaptersonphysicallayerauthenticationincludediscussiononthetheoretical
limitsofauthentication,aswellasprovideathoroughsurveyofphysicallayerau-
thentication,withspecialattentiondevotedtoaddressingthetime-varyingnatureof
thewirelesschannel.
Lastly, welookattwootheraspectsrelatedtosecurityandphysicallayercom-
munication.Cooperativecommunicationsisanemergingtechniquetoimprovethe
channel capacity of wireless communication systems, and involves multiple enti-
tiesassistingeachotherinthetransmissionanddecodingofmessagesbyrelaying
x Preface
replicasoftransmittedmessages.Unfortunately,traditionalcooperativecommunica-
tionschemesassumethatallentitiesaretruswtworthyandfollowprotocolsprecisely,
andthusthesepromisingcommunicationschemesareparticularlysensitivetosce-
narioswhereentitiesfalselyormaliciouslycooperate.Wehaveincludedachapter
thatexaminesthesecurityissuesthatariseincooperativecommunications,andpro-
posesanimproveddesignforstrengtheningthesecurityofcooperativetransmission
schemesbycarefullyintegratingthenotionoftrustintocooperativecommunication
protocols. Ourfinalchapterdiscussestheissueofmodulationforensics, whichin-
volvesidentifyingthetypeofmodulationthatisbeingemployedwhenthereisno
priorinformationaboutthetransmitter.Thisisparticularlyimportantforemerging
wirelesssystems,suchascognitiveradiosystems,wheretheremaynotbeanyprior
relationshipbetweenatransmitterandareceiver,anditisnecessarytoidentifythe
communicationmethodsbeingemployedbeforecommencingwithcommunication.
Further, such analysis is also important in conducting attacks against the physical
layerasknowingwhatmodulationmethodsarebeingemployedallowsonetobest
adapttheirattacks,whetherattemptingtospoofanentityorinterferewiththatentity.
Wenotethatthephysicallayerforwirelesssystemsprovidesanexcitingcollec-
tionoftoolstoenhancesecuritythatisnotavailabletoonewhostrictlyemploysa
cryptographictoolkit.Traditionalhigher-layersecuritymethodsmustplayanimpor-
tantroleinsecuringcommunicationsandcertainlyphysicallayersecuritytechniques
shouldnotbeconsideredareplacementforwell-testedcryptographyalgorithmsand
securityprotocols. However, thepropertiesofthewirelessmediumareapowerful
sourceofdomain-specificinformationthatcanbeusedtocomplementandenhance
traditionalsecuritymechanismsthathasremained,todate,anuntappedresourceand
thusshouldbeconsideredasexpandingthetoolsavailabletoengineersseekingto
securewirelesssystems.Themethodsdescribedinthisbookwillserveasthebasis
for removing a potential weak link in the design of future wireless systems and,
as wireless systems become increasingly pervasive, we expect that physical layer
securitymethodswillbeveryusefulinthwartingattacksthatcannotbedealtwith
usingconventionalnetworksecuritymechanisms.
Contributors
BabakAzimi-Sadjadi IntelligentAutomationInc.,15400CalhounDrive,Suite
400,Rockville,MD20855,USA,e-mail:[email protected]
ErsenEkrem DepartmentofElectricalandComputerEngineering,Universityof
Maryland,CollegePark,MD20742,USA,e-mail:[email protected]
HeshamElGamal DepartmentofElectricalandComputerEngineering,Ohio
StateUniversity,Columbus,OH43210,USA,e-mail:[email protected]
ElzaErkip DepartmentofElectricalandComputerEngineering,Polytechnic
University,Brooklyn,NY11201,USA,e-mail:[email protected]
SatashuGoel CarnegieMellonUniversity,5000ForbesAvenue,Pittsburgh,PA,
USA,e-mail:[email protected]
LarryGreenstein WirelessInformationNetworkLaboratory(WINLAB),
RutgersUniversity,671Rt.1South,NorthBrunswick,NJ08902,USA,e-mail:
[email protected]
DenizGu¨ndu¨z DepartmentofElectricalEngineering,PrincetonUniversity,
Princeton,NJ08544,USAandDepartmentofElectricalEngineering,Stanford
University,Stanford,CA94305,USA,e-mail:[email protected]
ZhuHan ECEDepartment,UniversityofHouston,Houston,TX77004,USA,
e-mail:[email protected]
XiangHe DepartmentofElectricalandComputerEngineering,PennState
University,UniversityPark,PA16802,USA,e-mail:[email protected]
HisatoIwai DepartmentofElectronics,DoshishaUniversity,Kyoto,Japan,
e-mail:[email protected]
AggelosKiayias DepartmentofComputerandElectricalEngineering,University
ofConnecticut,Storrs,CT,USA,e-mail:[email protected]
DeepaKundur DepartmentofElectricalandComputerEngineering,TexasA&M
University,CollegeStation,TX77843,USA,e-mail:[email protected]
xi
xii Contributors
LifengLai DepartmentofSystemsEngineering,UniversityofArkansasatLittle
Rock,LittleRock,AR72204,USA,e-mail:[email protected]
ZangLi WirelessInformationNetworkLaboratory(WINLAB),Rutgers
University,671Rt.1South,NorthBrunswick,NJ08902,USA,
e-mail:[email protected]
YingbinLiang DepartmentofElectricalEngineering,UniversityofHawaii,
Honolulu,HI96822,USA,e-mail:[email protected]
W.SabrinaLin ECEDepartment,UniversityofMaryland,CollegePark,MD
20742,USA,e-mail:[email protected]
K.J.RayLiu ECEDepartment,UniversityofMaryland,CollegePark,MD
20742,USA,e-mail:[email protected]
RuohengLiu DepartmentofElectricalEngineering,PrincetonUniversity,
Princeton,NJ08544,USA,e-mail:[email protected]
WilliamLuh DepartmentofElectricalandComputerEngineering,TexasA&M
University,CollegeStation,TX77843,USA,e-mail:[email protected]
NarayanMandayam WirelessInformationNetworkLaboratory(WINLAB),
RutgersUniversity,671Rt.1South,NorthBrunswick,NJ08902,USA,e-mail:
[email protected]
SuhasMathur WirelessInformationNetworkLaboratory(WINLAB),Rutgers
University,671Rt.1South,NorthBrunswick,NJ08902,USA,e-mail:
[email protected]
AlejandraMercado ADG,HughesNetworkSystems,Germantown,MD,USA,
e-mail:[email protected]
RohitNegi CarnegieMellonUniversity,5000ForbesAvenue,Pittsburgh,PA,
USA,e-mail:[email protected]
H.VincentPoor DepartmentofElectricalEngineering,PrincetonUniversity,
Princeton,NJ08544,USA,e-mail:[email protected]
AlexReznik InterDigital,781ThirdAvenueKingofPrussia,PA,USA,e-mail:
[email protected]
HideichiSasaoka DepartmentofElectronics,DoshishaUniversity,Kyoto,Japan,
e-mail:[email protected]
ShlomoShamai(Shitz) DepartmentofElectricalEngineering,Technion-Israel
InstituteofTechnology,TechnionCity,Haifa32000,Israel,e-mail:
[email protected]
PredragSpasojevic WirelessInformationNetworkLaboratory(WINLAB),
RutgersUniversity,671Rt.1South,NorthBrunswick,NJ08902,USA,e-mail:
[email protected]