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Divide-and-Conquer Based Cooperative Jamming

Explore how cooperative jamming can address the challenge of multiple eavesdroppers in close proximity to enhance physical layer security. Learn smart strategies like Divide-and-Conquer and Helper-Based schemes to safeguard wireless communications from prying eyes.

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Divide-and-Conquer Based Cooperative Jamming

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  1. Divide-and-Conquer Based Cooperative Jamming Physical Layer Security Addressing Multiple Eavesdroppers in Close Proximity Zhihong Liu, Jiajia Liu, Nei Kato, Jianfeng Ma, and Qiping Huang School of Cyber EngineeringXidian University, Xi’an, China

  2. Wireless Security Inherent Openness in wireless communications channel : Eavesdropping…..

  3. Motivations Alice wants to transmit secret message to Bob, but they do not share any common private key. If Eve is located outside the communication region, Alice and Bob can have a positive secrecy capacity, but …. Bob Alice … Eve may has channel advantage ! Eve … or more than one… … and some of them may locate quite close to Alice or Bob Important Challenge: the “near Eve” problem… ？ …and you very likely will not know where they are !

  4. Motivations • Cooperative Jamming In cooperative jamming, jammers transmit jamming signals at the same time when the source transmits the message, with the purpose of jamming eavesdroppers. Artificial noise [S. Goel and R. Negi, 2008] Medical devices[S. Gollakota, et al. , 2011] Virtual barriers [Y. Allouche, et al. , 2015] Sensor networks [I. Martinovic, et al. , 2009] [Courtesy: Şennur Ulukuş]

  5. Motivations • Many existing works on cooperative jamming have focused primarily on the simple model with single source-destination pair and single eavesdropper, • or investigate the secure connection from the information-theoretic perspective. [Courtesy: Matthieu Bloch] In practice, it is hard to achieve secure connection with the presence of multiple eavesdroppers in any location of the network.

  6. Basic Ideas We consider the following scenario: • A source-destination pair S-D without a common private key, and in the presence of multiple eavesdroppers, • the eavesdroppers may located near S or D, • no constrict on the number of eavesdroppers, • and no location knowledge of eavesdroppers is available. Approaches: • Smart Jamming Strategy (Divide and Conquer Method) • Helper-Based Two-Stage Scheme (addressing nearby eavesdroppers) • Cooperative Jamming Strategy

  7. Network Model • Nodes and eavesdroppers are distributed according to independent Poisson Point Processes (with intensities λ and λE). The eavesdroppers are passive, no collusion, and their location knowledge is unknown. • Wireless channel is modeled by large-scale fading channels. All nodes are equipped with a single omnidirectional antenna, and the network is interference limited. Rayleigh fading channels are also discussed. • Transmission is determined by the Signal to Noise Ratio (SNR) lying above a specified threshold. We require SNRSD ≥ γl and SNRSE< γe, where γe (< γl) can be arbitrarily small. Secrecy Capacity: CSD(E) = log2(1 + γl ) − log2(1 + γe ) wiretap channel code

  8. Smart Jamming Strategy Divide and Conquer Smart jamming strategy has three steps: • Jammer Selection and Power Adjustment : Choose t legitimate nodes to act as jammers, and tune each jammer’s transmit power PJ until SNRSD ≥ γl. • Block construction : M = M1⊕M2⊕ …⊕Mt, • Message Transmission: Transmit each block one by one. When a block is delivering, a jammer emits noise with proper power. Each jammer can jam a region. If t jammers can cover the whole communication region w.h.p., any eavesdropper will lose at least one block and can not recover the message.

  9. Smart Jamming Strategy Example • Block construction : M M1 M2 M3 M4 M5 M6 • Send each in a separate transmission If there are enough jammers, any eavesdropper in the network is guaranteed to be covered w.h.p.. Success…… Outage…… S D Jammer Node Eavesdropper

  10. Secure Connection Probability We define the secure connection probability Pc to be the probability that the message M can be securely transmitted from S to D When dSD is large,

  11. Secure Connection Probability • When γl = γe, the probability of the existence of a secure link S-D is

  12. Secrecy Coverage • If the intensity λ is large, the jamming regions can cover the whole communication region w.h.p., then the communication from S to D is secure, no matter how many eavesdroppers located within the whole communication region. Suggest E(Pcover) → 1−ϵ, then is required which is independent of λE.

  13. Secrecy Rate Maximization • In practice, we divide message into t blocks and send them in t separate transmissions. More rounds of transmissions will lead to less secrecy rate, RSD = 1/t [log2(1 + γl) − log2(1 + γe)],there is a tradeoff between secrecy rate and security.

  14. Nearby eavesdropper problem • Nearby Eavesdropper Problem • Eavesdropper near the source (or destination) is difficult to be jammed. • Some methods • Network Coding, • Guard Zone, • …… Outage probability with eavesdroppers in different location. If Eve is near S or D，the Outage probability is very high. The eavesdropper near S or D has a very small masking region

  15. Helper-Based Two-Stage Scheme • The communication is aided by a helper and consists of two stages: • Stage 1: The source S transmits signal, the destination D transmits jamming signal at the same time. • Stage 2: A helper H amplifies and forwards a weighted version of the mixture signal that it received in stage 1. Stage1 Stage2 YH Helper XH Helper H H XS XD YD S D S D E E YE1 YE2 Since node D has perfect knowledge of the jamming signal XD transmitted in Stage 1, it can cancel the jamming signal XD from YD while an eavesdropper cannot achieve this.

  16. Cooperative jamming • A Helper-Based Two-Stage Scheme from S to D to jam Eve near D. • SD：Message MS • Another Helper-Based Two-Stage Scheme from D to S to jam Eve near S. • SD：Message MD Hsd • Smart Jamming Strategy to jam Eve in other region. • SD：M1,M2,…,Mt • M = (MS ⊕ MD) ⊕ M1⊕…⊕Mt Hds S D Helper-Based Two-Stage Scheme + Smart Jamming Strategy

  17. Cooperative jamming Cooperative jamming strategy exhibits better performances than the smart jamming strategy in terms of Secure Connection Probability and Secrecy Rate. Secrecy Rate:

  18. Addressing fading channels Rayleigh fading channel： The fading gain |hij|2follows an exponential distribution and E[|hij|2] = 1 Secrecy Outage Probability ：

  19. Fading channels Helper Helper-Based Two-Stage Scheme Cooperative Jamming Smart Jamming Strategy The region near the source S is not jammed Only region near S and D is jammed The whole communication region is almost covered. Rayleigh fading channel

  20. Conclusions • Cooperative jamming is a powerful tool to increase the security of wireless networks: • It can jam eavesdroppers anywhere in the network, even they are located quite close to the source or the destination, • and can tolerate any number of independent eavesdroppers. • Many problems: • implementing in the existing infrastructure • better modeling adversary –e.g., active adversaries • combining with cryptographic method • …

  21. Thanks !

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