Secure Localization Services

Badri NathDept. of Computer Science/WINLABRutgers UniversityJointly with Wade Trappe, Yanyong Zhang WINLAB IAB meetingNovember, 2004

badri@cs.rutgers.edu

Importance of localization

Wireless/ Ad-hoc network

Localization infrastructure

ResourceAllocation

Services Resourcecontrol

Location dependent

Importance of localizationResource allocation– E.g., spectrum

allocationNodes in L1 use f1

Nodes in L2 use f2L1

L2

Requests from floor2 should go to print2

Importance of localizationLocation dependent services

All items (assume have RFID tags) in Aisle1 is 10% off!!

Route to your nearest peer

Importance of localizationResource control

Laptop cannot leave this building

Secret.file can only be opened from this room

Enforce location-dependent security policy

Secure LocalizationSecurity: Bad guys should not perturb your true location– Am I really here? Are you really there?

• Security, Authentication

Privacy: Bad guys should not know your true location– I am not really here! Guess where I am!– Marco Gruteser @WINLAB

What is Localization?Goal: Determine the location of one or more wireless devices based on some form of measurementsUseful measurements:– Time of flight (TOA)– Time difference of flight (TdOA)– Energy of flight (DoA based on Signal Strength)– Phase of flight (AoA = Angle of arrival from fixed stations)– Perspective of flight (Visual Cues)– Hop count to anchors: Correlated with distance– Neighbor Location: Find regions

Use Neighbor Locations: CentroidsScenario:– A set of anchor nodes

with known locations are deployed as infrastructure for localization

Wireless devices localize by calculating the centroid of the anchor points they hear:

)y,x( 11

⎟⎠⎞

⎜⎝⎛ ++++++

=n

yyy,n

xxx)y,x( n21n21 LL

)y,x( 22

)y,x( 44

)y,x( 33

)y,x( 55

Signal StrengthUnderlying Principle: Signal strength (RSSI) is a function of distanceUse known landmark locations and RSSI-Distance relationship to setup a least squares problem or have a mappings that can determine location from potential signal strength readings from know anchors (access points).

A1, S1; A2, S2; A3 S3 x,y

Localization :Hop-Count MethodsDV-hop localization algorithm: Obtain the hop counts between a sensor node and several locators.Translate hop counts to actual distance.Localize using triangulation.

L1

A

L2

L3

It is critical to obtain the correct hop counts between sensor nodes and every locator.

Attacks on LocalizationMost security and privacy issues for wireless networks are best addressed through cryptography and network securityEnd of Day Analysis: Not all security issues can be addressed by cryptography!Non-cryptographic attacks on wireless localization:– Adversaries may affect the measurements used to conduct

localization– Adversaries may physically pick up and move devices– Adversaries may alter the physical medium (adjust

propagation speed, introduce smoke, etc.)– Adversaries can shorten routing path (hop count)– Many, many more crazy attacks…

Signal Strength Attack on LocalizationSignal strength wireless localization are susceptible to power-distance uncertainty relationshipsAdversary may:– Alter transmit power of

nodes– Remove direct path by

introducing obstacles– Introduce absorbing or

attenuating material– Introduce ambient channel

noise

DistancePo

wer

Rec

eive

dd1 d2

Transmit Power Uncertainty

Location Uncertainty

Defenses for Wireless LocalizationMultimodal Localization:– Most localization techniques employ a single property– Adversary only has to attack one-dimension!!!– Defense Strategy: Make the adversary have to attack several

properties simultaneously– Example: Do signal strength measurements correspond to TOF

measurements?

Robust Statistical Methods:– Defense Strategy: Ignore the wrong values introduced by

adversaries– Develop robust statistical estimation algorithms and data

cleansing methods– Interesting behavior: Its best for the adversary not to be too

aggressive!

Least median squaresLeast squares

Least median squares

∑=

−−+−=N

iiiiyx

dyyxxyx1

220

20),(00 ))()((minarg)ˆ,ˆ(

00

220

20),(00 ))()((medminarg)ˆ,ˆ(

00iiiyx

dyyxxyx −−+−=

Attacks on Hop-Count Methods

L

A

hop_count (L->A) = 7

L

A

wormhole

hop_count (L->A) = 3

L

A

jammed area

hop_count (L->A) = 10

Spatial challenge-responseWhat else do you see test?Each node asked to ping a random set of trusted nodesEstimate of hop count can eliminate false readings

L

A

Conclusion and RemarksWireless localization algorithms are important to future location-based servicesMany strategies to cope with the effects of attacks on localization– Multimodal Localization– Robust Statistical Localization– Spatial challenge-response

FutureSecure localization offered as serviceSoftware, hardware, firmware support

SLSinside

You are at

I am at

Related workNew Field: Securing Wireless Localization– “Secure Verification of Location Claims,”

• Sastry and Wagner– “Secure Positioning in Sensor Networks,”

• S. Capkun and J.P. Hubaux– “SeRLoc: Secure range-independent localization for

wireless networks,”• L. Lazos and R. Poovendran

– “Securing Wireless Localization: Living with Bad Guys,”

• Z. Li, Y. Zhang, W. Trappe and B. Nath (expanded version under submission)