1. 1 Secure Cooperative MIMO Communications Under Active Compromised Nodes Liang Hong, McKenzie McNeal III, Wei Chen College of Engineering, Technology, and Computer Science Tennessee State University Dr. Liang Hong LHONG@TNstate.edu (615) 963-5364 College of Engineering, Technology, and Computer Science Tennessee State University

2. 2 Outline Introduction System Model Compromised Nodes Detection and Symbol Recovery Cooperative Transmission and Security Key Management Schemes Simulations Conclusions Secure cooperative MIMO communications under active compromised nodes Dr. Liang Hong LHONG@TNstate.edu (615) 963-5364 College of Engineering, Technology, and Computer Science Tennessee State University

3. 3 Introduction Wireless sensor networks (WSNs) have been widely deployed in −Military sensing and tracking, environment monitoring, smart home appliances management, health care, etc −WSNs are expected to be the basic building block of pervasive computing Cooperative MIMO can achieve the benefits of MIMO technique without the need of multiple antennas at each sensor node −MIMO can provide significant increases in data rate and link range without additional bandwidth or transmission power −Physical implementation of multiple antenna at a small node is not feasible −Distributed individual single-antenna nodes cooperating on data transmission and reception as a multi-antenna MIMO node Dr. Liang Hong LHONG@TNstate.edu (615) 963-5364 College of Engineering, Technology, and Computer Science Tennessee State University Secure cooperative MIMO communications under active compromised nodes

4. 4 Many WSNs have mission-critical tasks, however, the involvement of multiple nodes for transmission and/or receiving poses a challenge to the reliability of the information Node compromise is one of the most detrimental attacks −Active attack: the compromised nodes maliciously modify the relay information and inject falsified information (more severe than passive attacks) Previous security schemes either did not detect and defend against node compromise or needed extra MIMO antennas to achieve data assurance. Dr. Liang Hong LHONG@TNstate.edu (615) 963-5364 College of Engineering, Technology, and Computer Science Tennessee State University Secure cooperative MIMO communications under active compromised nodes

5. 5 Our previous work proposed a cross-layer security scheme that combined a cryptographic technique implemented in higher layer with data assurance analysis at the physical layer −Has much less bit errors −Receiving cluster periodically detects compromised nodes −The transmitting and receiving cluster have equal numbers of nodes −Only one compromised node is present in the transmitting cluster −No compromised node is present in the receiving cluster Dr. Liang Hong LHONG@TNstate.edu (615) 963-5364 Develop compromised node detection algorithm for more general scenarios. Research objectives College of Engineering, Technology, and Computer Science Tennessee State University Secure cooperative MIMO communications under active compromised nodes

6. 6 System Model Multi-hop cooperative MIMO system Dr. Liang Hong LHONG@TNstate.edu (615) 963-5364 Cooperative strategy: decode-and-forward College of Engineering, Technology, and Computer Science Tennessee State University Secure cooperative MIMO communications under active compromised nodes

7. 7 (1) Received signal : received signals at the receiving cluster : additive Gaussian noise components, they are identically distributed and mutually statistically independent, each with a zero mean and a power spectral density Dr. Liang Hong LHONG@TNstate.edu (615) 963-5364 : transmitted signals at the transmitting cluster : channel matrix (m R  m T ) College of Engineering, Technology, and Computer Science Tennessee State University Secure cooperative MIMO communications under active compromised nodes

8. 8 Compromised Nodes Detection and Symbol Recovery Dr. Liang Hong LHONG@TNstate.edu (615) 963-5364 Methodology: The CH h of B will perform compromised nodes detection at random time t in each time interval with adaptive security level College of Engineering, Technology, and Computer Science Tennessee State University Secure cooperative MIMO communications under active compromised nodes

9. 9 Dr. Liang Hong LHONG@TNstate.edu (615) 963-5364 Compromised nodes detection algorithm 1.The CH h of B requests each of the primary nodes in B to send the received symbols to h. Then h obtained the combined signal 2.Node h uses Inverse Channel Detector to estimate the transmitted symbols s, i.e.,, where W is an m R  m T weighing matrix 3.Since all data streams are the same, h can identify the compromised node x if x didn’t transmit the supposed symbol. –For example, assuming that the primary node x in A is compromised and it is the jth node in A, if s j from step 2 is not the same as the information recovered from the majority of the other nodes, x will be classified as a compromised node College of Engineering, Technology, and Computer Science Tennessee State University Secure cooperative MIMO communications under active compromised nodes

10. 10 Dr. Liang Hong LHONG@TNstate.edu (615) 963-5364 Scenario 1: The transmitting and receiving clusters have different number of nodes (2) Scenario 2: More than one compromised node is present in the transmitting cluster In step 3, the recovered data streams from different transmitting nodes will be sorted into groups, where nodes are assigned to the same group if they contain identical symbols. −The group with largest number of nodes is assumed to contain the IDs of trustworthy nodes. All the other nodes are classified as compromised nodes. −If all the groups have the same number of IDs, all the nodes in transmitting cluster are classified as compromised nodes. College of Engineering, Technology, and Computer Science Tennessee State University Secure cooperative MIMO communications under active compromised nodes

11. 11 Dr. Liang Hong LHONG@TNstate.edu (615) 963-5364 Scenario 3: Compromised nodes are present in the receiving cluster 1.The CH h in B performs inverse channel detection on the set of received data from each node in B. 2.If two or more of the estimates of the transmitted symbols are the same, then this node in B is not compromised. Its ID will be saved in the trustworthy node group. 3.If none of the estimates of the transmitted symbols are the same, then this node in B is the compromised node. 4.After all the compromised nodes in B are identified, all the trustworthy nodes in B will be used to identify the compromised nodes in A. Using the algorithm in Scenario 2, the compromised nodes in A can be detected College of Engineering, Technology, and Computer Science Tennessee State University Secure cooperative MIMO communications under active compromised nodes

12. 12 Dr. Liang Hong LHONG@TNstate.edu (615) 963-5364 Symbol recovery: When the compromised nodes are detected in the transmitting cluster −the CH h in B will send each node in its cluster the information of the compromised nodes in A. −When the node v in B receives this information, it decodes the message by simply setting the columns in channel matrix that corresponds to the compromised nodes to zero When the compromised nodes are detected in the receiving cluster −The CH h in B will send the IDs of the trustworthy nodes to the CH in its next relay. −In the next relay, simply setting the column in channel matrix that corresponds to these compromised nodes to zero. −If compromised nodes are detected in the last receiving cluster, the sink node will use the received data from the trustworthy nodes for symbol detection College of Engineering, Technology, and Computer Science Tennessee State University Secure cooperative MIMO communications under active compromised nodes

13. 13 Cooperative Transmission and Security Key Management Schemes The cooperative transmission and security key management schemes proposed in our previous work will be used to provide secure cooperative communications. This security scheme provides secured communication between uncompromised nodes. By combining the compromised nodes detection algorithm, the security of the system will be largely enhanced. Dr. Liang Hong LHONG@TNstate.edu (615) 963-5364 College of Engineering, Technology, and Computer Science Tennessee State University Secure cooperative MIMO communications under active compromised nodes

14. 14 Dr. Liang Hong LHONG@TNstate.edu (615) 963-5364 Type of Keys (1) Each cluster: each node has a cluster key C-key(A) for local transmission (2) Each link AB: each node in A and B has a key L-key(A,B) for long-haul transmission between A and B Secured cooperative relay: Step 1 (Local transmission at A): Each node in A encrypts its information with C-key(A), and broadcasts it to other local nodes using different timeslots. Each node uses C- key(A) to decrypt the received m information back. Step 2 (long-haul transmission between A and B): Each node i in A encrypts sequence I with key L-key(A,B), and it acts as ith antenna encoding the encrypted I. Then, all m nodes in A broadcast the encrypted and encoded I to the nodes in B at the same time. When a nodes in B receives m copies of the information, it decrypts them with L- key(A,B), and then decode them back to I. College of Engineering, Technology, and Computer Science Tennessee State University Secure cooperative MIMO communications under active compromised nodes

15. 15 Simulations The channels are block Rayleigh fading channels. It is constant during the transmission of one symbol, but is randomly changing between symbols Different channels are identically distributed and statistically independent. Binary phase shift keying (BPSK) is chosen as the modulation scheme. 100 received symbols are used in the proposed algorithms for compromised nodes identification. The maximum likelihood detector is used for symbol demodulation Dr. Liang Hong LHONG@TNstate.edu (615) 963-5364 College of Engineering, Technology, and Computer Science Tennessee State University Secure cooperative MIMO communications under active compromised nodes

16. 16 Dr. Liang Hong LHONG@TNstate.edu (615) 963-5364 For scenario 1 and 2 Detection Accuracy Performance Comparison College of Engineering, Technology, and Computer Science Tennessee State University Secure cooperative MIMO communications under active compromised nodes

17. 17 Dr. Liang Hong LHONG@TNstate.edu (615) 963-5364 For scenario 1 and 3 Detection Accuracy Performance Comparison College of Engineering, Technology, and Computer Science Tennessee State University Secure cooperative MIMO communications under active compromised nodes

18. 18 Conclusions Algorithms for compromised nodes detection are proposed for three more general scenarios. The proposed compromised nodes detector are then used in a cooperative MIMO communication system to enhance the security. The compromised nodes detector has high detection accuracy. The reliability of the information is significantly improved. Dr. Liang Hong LHONG@TNstate.edu (615) 963-5364 College of Engineering, Technology, and Computer Science Tennessee State University Secure cooperative MIMO communications under active compromised nodes

19. 19 Dr. Liang Hong LHONG@TNstate.edu (615) 963-5364 College of Engineering, Technology, and Computer Science Tennessee State University Secure cooperative MIMO communications under active compromised nodes Thank you! Questions?