If covert communication is employed, an opponent might not be conscious of the communication taking place intermediary to the 2 users. This study investigates covert wireless mode-based interactions in a thickly distributed IoT connection wherein 1 IoT gadget experiences noise from the background as well as combined interference caused by remaining Tx devices. Communication with covertness gets challenging in a network of IoT devices using THz (Terahertz) Band because Willie can effortlessly place a receiving medium in the tiny beam separating Bob and Alice to detect or prohibit their LOS links. We demonstrated that communication with covertness remains viable in this circumstance by making use of diffuse scattering or reflection from a surface that’s rough. With regards to the security of the physical layer, communication with covertness could increase the security of the IoT connection from the bottom layer up. Between 300 and 350 GHz is the lowest frequency range that can be used in a covert environment without having any negative effects on covert communications. The effect will be exponentially grown as we reduce the frequency ranges, which will be validated via the simulation and its outcomes.
If covert communication is employed, an opponent might not be conscious of the communication taking place intermediary to the 2 users. This study investigates covert wireless mode-based interactions in a thickly distributed IoT connection wherein 1 IoT gadget experiences noise from the background as well as combined interference caused by remaining Tx devices. Communication with covertness gets challenging in a network of IoT devices using THz (Terahertz) Band because Willie can effortlessly place a receiving medium in the tiny beam separating Bob and Alice to detect or prohibit their LOS links. We demonstrated that communication with covertness remains viable in this circumstance by making use of diffuse scattering or reflection from a surface that’s rough. With regards to the security of the physical layer, communication with covertness could increase the security of the IoT connection from the bottom layer up. Between 300 and 350 GHz is the lowest frequency range that can be used in a covert environment without having any negative effects on covert communications. The effect will be exponentially grown as we reduce the frequency ranges, which will be validated via the simulation and its outcomes.
Covert communication can prevent an adversary from knowing that a transmission has occurred between two users. In this article, we consider covert wireless communications in an Internet-of-Things (IoT) network with dense deployment, where an IoT device experiences not only the background noise but also the aggregates interference from other Tx devices. Our results show that in a dense IoT network with lower frequency AWGN channels, when the distance between Alice and the adversary Willie da,w= ω(n1/(2α)), Alice can reliably and covertly transmit O(log2√n) bits to Bob in n channel uses. In an IoT network with terahertz (THz) band, covert communication is more difficult because Willie can simply place a receiver in the narrow beam between Alice and Bob in order to detect or block their line-of-sight communications. We demonstrated that covert communication is still possible in this occasion by utilizing the reflection or diffuse scattering from a rough surface. From the physical-layer security perspective, covert communication can enhance the security of IoT network from the bottom layer.
Covert communication can prevent an adversary from knowing that a wireless transmission has occurred. In additive white Gaussian noise (AWGN) channels, a square root law is found that Alice can reliably and covertly transmit O(n) bits to Bob in n channel uses. In this paper, we consider covert communications in noisy wireless networks, where the receivers not only experience the background noise, but also the aggregate interference from other transmitters. Our results show that uncertainty in interference experienced by the adversary Willie is beneficial to Alice. In AWGN channels, when the distance between Alice and Willie da,w=ω(n1/(2α)) (α is the path loss exponent), Alice can reliably and covertly transmit O(log2n) bits to Bob in n channel uses. Although the covert throughput is lower than the square root law, the spatial throughput is higher. In THz (Terahertz) Band networks,covert communication is more difficult because Willie can simply place a receiver in the narrow beam between Alice and Bob to detect or block their LOS (Line-of-Sight) communications. We then present a covert communication scheme that utilizes the reflection or diffuse scattering from a rough surface to prevent being detected by Willie. From the network perspective, the communications are hidden in the interference of noisy wireless networks, and what Willie sees is merely a "shadow" wireless network.
We propose a physical-layer security approach based on the concept of steganography for IoT networks. Similar to the covert communications, the transmitter (Alice) attempts to send her secret signal to the legitimate receiver (Bob) avoiding being detected by the warden (Willie). Instead of sending the weak signal that is barely detectable by Willie, we hide secret signal in the cover signal that is transmitted over the same channel such that its existence may not be easily detected without any knowledge of prior information. Considering the practical applications to IoT networks, the DFT-precoded OFDM is adopted for the cover signal and conventional OFDM for the secret signal. Through theoretical analysis and corresponding simulations, the detection error probability of Willie is evaluated over an AWGN channel, revealing that judicious selection of cover signal power may increase the detection error probability of Willie and thus improve the covertness.
In the context of Internet-of-Things (IoT) applications, ensuring secure and covert wireless communication remains a critical challenge, especially when using energy harvesting relays. Moreover, the analysis of hardware impairments is a pivotal practical aspect in the evaluation of IoT communication networks. This paper investigates four scenarios to address security and covert communication. In the first scenario, the focus is on guaranteeing the security in the presence of hardware impairments. In this case, the external jammer transmits interference signals toward both the relay and Bob to prevent information leakage from the untrusted relay. However, in this scenario, since the state of the untrusted relay is always superior to that of Bob, security cannot be guaranteed under any network parameters. Accordingly, in the second scenario, to tackle this problem, a receiver equipped with the capability to transmit jamming signals (receiver jammer) is proposed, aiming to protect the communication against potential information leakage from the untrusted relay. In the third and fourth scenarios, the relay is considered a trusted node, and warden (Willie) is introduced into the system. Here, the external jammer plays a crucial role when transmitting interference signals simultaneously toward Bob, relay, and Willie to ensure communication security. This scenario incorporates covert communication designed to counter threats from Willie’s detection. Covert communication in these two scenarios is analyzed under the following two conditions: 1) When Willie has Channel State Information (CSI); 2) When Willie lacks CSI, in which case he equips himself with multiple antennas. Simulation results show that the proposed power allocation can enhance secure and covert communications, even in the presence of hardware impairments and a multi-antenna Willie. Moreover, it is shown that when Willie has CSI, the performance of covert communication is severely reduced.
In this chapter, we described the fundamental system model, challenges, and technical solutions to THz physical layer security. Despite the good security performance provided by the high directivity of THz wireless communications, THz physical layer security still faces security challenges, including eavesdroppers inside beam sector, eavesdroppers in close proximity and THz covertness problem. In light of these challenges, three THz-specific security schemes were described. First, the DA-APM proposes to transmit signals at sides of molecular absorption peaks to enhance the wireless security and covertness. This scheme effectively combats eavesdroppers inside the beam sector and can even enhance the covertness of THz wireless communications. Second, the SIC-free RAN scheme takes the advantage of the distance-dependent temporal broadening effect to jam Eve in close proximity while not jamming Bob. This method handles the eavesdroppers in close proximity with a lower-complexity receiver AN mechanism. Third, we described the WSA and beamforming scheme to combat near eavesdropping without the aid of other nodes. The size rationality of practical THz WSA is justified.Despite the fruitful research progress on THz physical layer security, there are still open challenges remaining to be tackled, which are described as follows. First, since the optimal molecular absorption coefficients depend on the propagation distance, it is necessary to adjust the carrier frequency as the distance between Alice and Bob varies. How to efficiently and practically tune the carrier frequency to use proper sub-bands needs investigation. Second, the hybrid beamforming structure is usually adopted in THz communications. However, the hybrid beamformer design for the WSA is a non-convex optimization problem. It is necessary to investigate efficient and low-complexity solutions for the WSA beamformer design. Finally, active security attacks, for instance, eavesdroppers may send the jamming signal to the legitimate receiver while overhearing the secret message, need to be handled for THz physical layer security. In line with this, security mechanisms simultaneously combating active and passive eavesdropping are awaited to be explored as a future direction.
Covert wireless communication can prevent an adversary from knowing the existence of user's transmission, thus provide stronger security protection. In AWGN channels, a square root law was obtained and the result shows that Alice can reliably and covertly transmit O(n) bits to Bob in n channel uses in the presence of a passive eavesdropper (Willie). However, existing work presupposes that Willie is static and only samples the channels at a fixed place. If Willie can dynamically adjust the testing distance between him and Alice according to his sampling values, his detection probability of error can be reduced significantly via a trend test. We found that, if Alice has no prior knowledge about Willie, she cannot hide her transmission behavior in the presence of an active Willie, and the square root law does not hold in this situation. We then proposed a novel countermeasure to deal with the active Willie. Through randomized transmission scheduling, Willie cannot detect Alice's transmission attempts if Alice can set her transmission probability below a threshold. Additionally, we systematically evaluated the security properties of covert communications in a dense wireless network, and proposed a density-based routing scheme to deal with multi-hop covert communication in a wireless network. As the network grows denser, Willie's uncertainty increases, and finally resulting in a "shadow" network to Willie.