Natraj Jaganmohan (njaganm)
Sandeep A Rao (sarao)
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 Background about Cognitive Radio Networks
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Primary User Emulation Attack (PUEA)
Existing approaches to solve PUEA.
 PUEA attack model with Directional antennas.
 Attack mitigation using TOE estimation.
 Simulation results.
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Limitations of the approach.
Future directions of research.
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“All consumers . . . deserve a new spectrum policy paradigm that is rooted in modern-day technologies and markets. We are living in a world where demand for spectrum is driven by an explosion of wireless technology and the ever-increasing popularity of wireless services.
Nevertheless, we are still living under a spectrum 'management' regime that is 90 years old. It needs a hard look, and in my opinion, a new direction.”
Michael K. Powell (Chairman FCC Spectrum
Policy Task Force)
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Cognitive Networks help us solve the problem.
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Background: Cognitive Radio Networks.
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Wireless spectrum is very scarce leading to spectrum crisis.
FCC recommends use of opportunistic or cognitive networks to increase spectrum utilization.
This technology would put unused and under-used spectrum assets to work – without impacting primary users within those bands. It is a bold, yet workable solution.
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Background: Cognitive Radio Networks.
 “A Cognitive Radio is a radio frequency transmitter/receiver that is designed to intelligently detect whether a particular segment of the radio spectrum is currently in use, and to jump into (and out of, as necessary) the temporarily-unused spectrum very rapidly, without interfering with the transmissions of other authorized users.”
 http://www.ieeeusa.org/forum/POSITIONS/cognitiveradi o.html
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Cognitive Radio networks operation:
PU-Tx
PU-RX
SU
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PU-RX
SU
PU-RX
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What makes Cognitive Networks possible?
Key enablers of CRNs:
 Radio manufacturers have started to create flexible software-defined radios.
 Research funding and support for spectrum reuse.
 Support for Dynamic Channel selection, channel scanning and adjustable transmission power.
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Some terminologies used in this presentation:
 CRN: Cognitive Radio Network
 PU: Primary User (licensed user)
 SU: Secondary user (CRN node)
 PUEA: Primary User Emulation Attack
 FC: Fusion Center
 TOE: Time of Emission
 TOA: Time of Arrival.
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Most important attacks on CRNs
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Spectrum data falsification attacks: In this case, one or more SUs are compromised and hence report wrong sensing values to
FC. This makes the FC make incorrect decision about the presence of PU.
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The most preferred way to mitigate the attack is to collect sensing values from a group of SUs and remove the outlier values.
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Primary User Emulation Attack:
Primary Transmitter
PU1
PU2
SU1
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PU3
SU2
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Primary User Emulation Attack:
Primary Transmitter
PU1
PU2
Attacker
SU1
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PU3
SU2
SUs cannot access channel as they think PU is transmitting
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Secondary users cannot authenticate the
PU transmission.
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FCC states that PU cannot be modified to support security. Hence regular authentication schemes don’t work.
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General approaches to defeat this attack:
Solution 1

RSSI based PU localization:
(x,y)
Decision is made based on all received sensing reports
FC
RSSI values are measured at all SUs and calculate the location of PU.
Ideal case of a PU transmitting, all RSSI values will be correct w.r.t distance
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Zhou Yuan et al, suggested the use of localization schemes to estimate and authenticate the location of PU.
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Scheme based on Received signal power.
Pr = Pt + a 10 log (do/d) + w
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It can be defeated by attacker by using
Antenna arrays with different power levels.
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General approaches to defeat this attack: Solution 2

Dr. Peng Ning et al proposed integrating cryptographic signatures and wireless link signatures to enable primary user detection. Essential to the approach is a helper node placed physically close to a primary user.
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General approaches to defeat this attack: Solution 2

Working with helper nodes.
(x,y)
Helper Node
Helper node transmits signals identical to PU
SUs can try to verify the PU authenticity by verifying the
Wireless Link signature of Helper node
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General approaches to defeat this attack: Solution 2
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This technique is very effective in terms of authenticating primary user. We exploit the proximity of Helper node with
PU.
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Problem is the authentication of wireless link signature of the helper node. Also if attackers are placed near helper nodes, then it causes problems.
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General approaches to defeat this attack: Solution 3
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IRIS model proposed by Alexander et al, has a secure attack detection by verifying the consistency of system state (Transmit power and path loss).
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This technique is very effective and it defeats both Data Falsification attacks and
PUEA. But, it fails in the case of attacker with antenna arrays and directional antenna.
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All nodes are loosely time synchronized.
Location of PU is fixed and known to all
SUs.
Fusion Center is used to make decision about presence of PU.
All SUs are connected to FC using a secure link.
There is a LOS path between every SU and PU.
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This attack model fails all the localization based solutions for PUEA which have been proposed previously.
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Attacker uses a multi antenna array or
MIMO technology with directional antennas to send PU-TX like signals to different SUs with various power levels faking the presence of PU.
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The power levels at different nodes are expected with respect to the distance from the PU-TX.
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Antenna array – multiple antenna transmitter
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This attack is possible because:
1. Antenna arrays are low cost and easy to setup
2. Attacker can manipulate the power levels in each directional beam from every antenna element to make sure every SU calculates the RSSI equal to the RSSI when PU transmits.
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
We have simulated the attack model to verify whether such an attack is really possible.
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Modeler: Opnet Network modeler 16
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Attack model: Directional Antenna pattern formation in Opnet
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Attack model: Directional Antenna pattern formation in Opnet
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Attack model: Directional Antenna pattern formation in Opnet
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Attack model: A sample scenario proving the possibility of attack
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Attack model: Throughput graphs.
PU-TX
(antenna 1)
SU-1
SU-2
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Attack model: Multiple antenna array simulation.
Ref: http://fens.sabanciuniv.edu/telecom/eng/comnet/cisco/smart.htm
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Hence if the attacker can configure each antenna element with the appropriate power levels to produce required RSSI values at each SU, then attack is achieved.
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Regular localization based methods cannot defeat this attack. This forms the motivation for our solution.
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SU
Fusion
Center
SU
SU
SU
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PU
PUE
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Secondary Users and Fusion Center
◦ are loosely Synchronized
◦ have secure communication
Fusion Center
◦ cannot be compromised
◦ knows locations of all users (secondary as well as primary)
◦ has good computational power and storage
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Can use antenna array
◦ But transmitting with a beam formation at different locations at different times is restricted.
Multiple Attackers can coordinate
◦ They can be synchronized among themselves
Attacker knows location of all nodes
SU may be compromised
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Sensors measure Time of Arrival
Fusion Center estimates Time of Emission
Robust against,
◦ Multiple, coordinated attackers
◦ Multiple compromised secondary users
◦ Node with Antenna Array!
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TOA SU
Estimate TOA!
PU
PUEA result
TOA
SU
Estimate TOA!
Fusion
Center
PUEA result
Estimate TOE!
TOE estimated for every sensor must be almost same in an ideal scenario
In the presence of an attack there will be deviations in some TOE estimations
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Time
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FC
TOA
TOA
TOA
FOR EACH NODE MEASURE TOE!
TOA
TOA
TOEi = TOAi – Dist/c + ξ
COMPUTE MEAN  TOEmean
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FOR EACH NODE, MEASURE DEVIATION!
δ i = TOEAVG ~ TOEi
If δ i > μ Increment C
μ -> Maximum allowable deviation!
C -> number of deviated values
If C > k then PUEA!
k -> Maximum no. of allowable deviated reports
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
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Determining μ
◦ The maximum deviation in the measurement by a node under a non-attack scenario!
Determining k
◦ Too small? Increase in false negative!
◦ Too large? Increase in false alarm!
◦ Tradeoff needed!
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
If an attacker is capable of compromising almost every node!
◦ Attacker too powerful!
◦ Note: We have a threshold which is used to tolerate certain number of configured node compromises. But, if almost all nodes in network are compromised, then the network is not useful.
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FCC may relax rule “no modification to the incumbent (primary) system should be required to accommodate opportunistic use of the spectrum by secondary users”
◦ Already relaxed for wireless microphones
Removing Fusion Center
◦ May decrease latency and increase performance of system.
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An Attack Model against the approaches using RSSI is proposed and simulated
A Novel approach to mitigate PUEA is proposed using Time of Emission
Estimation and simulated
Approach is compared with a similar RSSI based approach
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