In this letter, we propose a novel scheme for enhancing the security of the information transfer between resource-limited devices. We select a pulse from a set of T-orthogonal pulses for shaping the data at source (S) based on legitimate channel state information (CSI). A destination (D) having the CSI, properly samples the output of the matched filter. An eavesdropper (E) having no knowledge of the legitimate CSI, may or may not sample correctly, thereby, inducing artificial intersymbol interference (ISI) at the E. We also consider a case where the S - E link is correlated with the S - D link (when E and D are closely located). We derive optimal thresholds at E, S for switching the selection of a pulse in maximizing and minimizing the achievable rate at E, respectively. We derive closed-form expressions for upper bound and lower bound on the secrecy outage probability (SOP) for the independent case. Simulation results show that unlike at D, the symbol error rate (SER) at E saturates at a high SER due to the induced ISI.
In this letter, we propose a novel scheme for enhancing the security of the information transfer between resource-limited devices. We select a pulse from a set of T-orthogonal pulses for shaping the data at source (S) based on legitimate channel state information (CSI). A destination (D) having the CSI, properly samples the output of the matched filter. An eavesdropper (E) having no knowledge of the legitimate CSI, may or may not sample correctly, thereby, inducing artificial intersymbol interference (ISI) at the E. We also consider a case where the S - E link is correlated with the S - D link (when E and D are closely located). We derive optimal thresholds at E, S for switching the selection of a pulse in maximizing and minimizing the achievable rate at E, respectively. We derive closed-form expressions for upper bound and lower bound on the secrecy outage probability (SOP) for the independent case. Simulation results show that unlike at D, the symbol error rate (SER) at E saturates at a high SER due to the induced ISI.
Secure communication over a wireless channel in the presence of a passive eavesdropper is considered. We present a method to exploit the eavesdropper's inherent receiver vulnerabilities to obtain everlasting secrecy. An ephemeral cryptographic key is pre-shared between the transmitter and the legitimate receiver and is utilized to induce intentional intersymbol interference (ISI). The legitimate receiver uses the key to cancel the ISI while the eavesdropper, since it does not have the key, cannot do such. It is shown that although ISI reduces the capacity of the main channel, it can lead to a net gain in secrecy rate. The achievable secrecy rates for different ISI filter settings are evaluated and the proposed method is compared with other information-theoretic security schemes.
Application of Internet of Things (IoT) in health, defense, banking, and other confidential information transfer urges the need for secure IoT. As most of the IoT devices are resource-limited (antennas, bandwidth, energy), securing the information transfer has always been a challenge. Looking at a solution for enhancing the security of single antenna, single carrier, energy efficient devices, we propose a novel scheme, channel-based mapping diversity. This scheme uses the inherent randomness of the wireless channel and multiple mappings available for an M-ary phase shift keying constellation in confusing an eavesdropper. When the legitimate and the eavesdropper channels are independent of each other, it is shown that a symbol error rate (SER) of (M-1)/ M is induced at the eavesdropper. Whereas, when the channels are correlated, optimal and suboptimal strategies at source and eavesdropper are derived for their respective optimal performances. Further, a closed-form expression for a lower-bound on the SER at the eavesdropper is derived. Simulation results show that for the correlated case, as SNR at the eavesdropper increases, SER initially decreases, later saturates to a relatively high SER, hence making the job of the eavesdropper difficult in getting the legitimate data. Furthermore, the effect of the correlation is more pronounced on SER at higher levels of correlation. This indicates that for practical correlation scenarios, SER is high enough to confuse the eavesdropper.
We investigate the physical layer security (PLS) in multi-user interference networks. In particular, we consider secure transmission from a legitimate source (Alice) to a legitimate destination (Bob), coexisting with multiple passive eavesdroppers (Eves), as well as multiple legitimate transceivers. By assuming that only statistical channel state informations (CSIs) of Eves and local CSIs of legitimate users are available, we propose an artificial noise (AN) assisted interference alignment (IA) for security enhancement. Unlike traditional IA based security approaches which may result in secret signal cancellation, we design a modified alternating minimization (AM) scheme to overcome this threat, by incorporating the max-eigenmode beamforming (MEB) for secure transmission. Moreover, by partitioning the IA equation into three independent subsets and their combinations, a much tighter necessary condition for IA feasibility is established. We also provide guiding insights into the practical system designs, including useful guidelines for the selection of the dimension of AN. Furthermore, the power allocation ratio between the secret signal and the AN signal is optimized to minimize the secrecy outage probability (SOP), subject to a minimum secrecy rate constraint. Numerical results demonstrate that our design can enhance both quality and security of the secret signal, and thus is suitable and reliable for PLS in interference networks.
The physical layer security problem with a passive eavesdropper is considered in this letter. We propose a method to obtain everlasting secrecy by exploiting inter-symbol interference (ISI) in eavesdropper. In the proposed method, the pulse shaping filter in the transmitter changes with time in the faster-than-Nyquist (FTN) signaling structure. The filter hopping pattern is pre-shared between the transmitter and the legitimate receiver. Knowing the hopping pattern, the legitimate receiver can mitigate the ISI as that in FTN. Otherwise, the eavesdropper will experience severe interference. The results show that even the eavesdropping link is much better than the legitimate link, a positive secrecy rate is also obtained. The secrecy rates for various examples of the proposed method are evaluated and the comparisons with other information-theoretic security schemes are also shown.
Passive eavesdropping compromises confidentiality in wireless networks, especially in resource-constrained environments where heavyweight cryptography is impractical. Physical layer security (PLS) exploits channel randomness and spatial selectivity to confine information to an intended receiver with modest overhead. However, typical PLS techniques, such as using beamforming, artificial noise, and reconfigurable intelligent surfaces, often involve added active power or specialized deployment, and, in many designs, rely on precise time synchronization and perfect CSI estimation, which limits their practicality. To this end, we propose AmbShield, an AmBD-assisted PLS scheme that leverages naturally distributed AmBDs to simultaneously strengthen the legitimate channel and degrade eavesdroppers' without requiring extra transmit power and with minimal deployment overhead. In AmbShield, AmBDs are exploited as friendly jammers that randomly backscatter to create interference at eavesdroppers, and as passive relays that backscatter the desired signal to enhance the capacity of legitimate devices. We further develop a unified analytical framework that analyzes the exact probability density function (PDF) and cumulative distribution function (CDF) of legitimate and eavesdropper signal-to-interference-noise ratio (SINR), and a closed-form secrecy outage probability (SOP). The analysis provides clear design guidelines on various practical system parameters to minimize SOP. Extensive experiments that include Monte Carlo simulations, theoretical derivations, and high-SNR asymptotic analysis demonstrate the security gains of AmbShield across diverse system parameters under imperfect synchronization and CSI estimation.
In this paper, we present a new secrecy-enhancing scheme for the spatial modulation (SM) system, by considering imperfect channel state information (CSI). In the proposed scheme, two antennas are activated at the same time. One of the activated antennas transmits information symbols along with artificial noise (AN) optimized under the imperfect CSI condition. On the other hand, the other activated antenna transmits another AN sequence. Because the AN are generated by exploiting the imperfect CSI of the legitimate channel, they can only be canceled at the legitimate receiver, while the passive eavesdropper will suffer from interference. We derive the secrecy rate of the proposed scheme in order to estimate the performance. The numerical results demonstrated in this paper verify that the proposed scheme can achieve a better secrecy rate compared to the conventional scheme at the same effective data rate.