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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)
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