Covert communications, or covert channels, are commonly exploited to establish a data exfiltration channel from an insider on a trusted network to a malicious receiver outside the network without using normal communication of the network. It is because the malicious receiver is an unauthorized user of the communication network and so he cannot communicate with any entity in the network. In this study, we construct a new covert wireless unidirectional communication mechanism in an IEEE 802.11 environment. Our covert communication is based on a covert timing channel exploiting the beacon interval of a given commercial-like AP. Because the wireless covert channel we proposed can be implemented only with firmware modification to the WLAN MAC protocol, it is very suitable for application in a real public AP environment. In order to dramatically reduce the chance of covert signals being detected by others, a new and simple covert data encoding scheme, called ping-pong covert timing channel (PPCTC), is proposed, and we show that the covertness of the PPCTC is excellent compared to the previous timing-based covert channels. Although this wireless covert communication is unidirectional communication, since PPCTC has recovery characteristics against consecutive 2-bit errors, stable communication is guaranteed. Furthermore, a covert frame structure is presented for providing the confidentiality and integrity of the information transmitted via our covert channel. To the best of our knowledge, this is the first attempt.

This paper proposes a long range-frequency hopping spread spectrum (LR-FHSS) transceiver design for the Direct-to-Satellite Internet of Things (DtS-IoT) communication system. The DtS-IoT system has recently attracted attention as a promising non-terrestrial network (NTN) solution to provide high-traffic and delay-tolerant data transfer services, such as wide-area situational awareness (WASA) in smart grids and car share management in automotive applications, to IoT devices in global coverage. In particular, this study provides guidelines for the overall DtS-IoT system architecture and design details that conform to the Long Range Wide-Area Network (LoRaWAN). Furthermore, we also detail various DtS-IoT use cases. Considering low-Earth orbit (LEO) satellites, we develop the LR-FHSS transceiver to improve system efficiency, which is a leading attempt to build practical satellite communication systems using LR-FHSS, excluding commercial products. Moreover, we apply a robust synchronization scheme against the Doppler effect and co-channel interference (CCI) caused by LEO satellite channel environments, including signal detection for the simultaneous reception of numerous frequency hopping signals and an enhanced softoutput-Viterbi-algorithm (SOVA) for the header and payload receptions. Lastly, we present proof-of-concept implementation and testbeds using an application-specific integrated circuit (ASIC) chipset and a fieldprogrammable gate array (FPGA) that verify the performance of the proposed LR-FHSS transceiver design of DtS-IoT communication systems. The laboratory test results reveal that the proposed LR-FHSS-based framework with the robust synchronization technique can provide wide coverage, seamless connectivity, and high-throughput communication links for the realization of future satellite communication networks.

Keeping IoT devices secure has been a major challenge recently. One of the possible solutions to secure IoT devices is to use a physically unclonable function (PUF). A PUF is a security primitive that can generate device-specific cryptographic information by extracting the features of hardware uncertainty. Because PUF instances are very difficult to replicate even by the manufacturer, the generated bit sequence can be used as cryptographic keys or as a unique identifier for the device. Regarding the implementation of PUF, the majority of PUFs introduced over the past decade are in the form of active components and have been implemented as separate chips or embedded as a part of a chip, making it difficult to use them in low-cost IoT devices due to cost and design flexibility. One approach to easily adopt PUFs in resource-constrained IoT devices is to use passive components such as resistors and capacitors (RC) that can be configured at low cost. The main feature of this RC-based PUF is that it extracts the small difference caused by charging and discharging of RC circuits and uses it as a response. In this paper, we extend the previous research and show the possibility to secure IoT devices by using the RC-based PUF.

In this paper, we propose hardware-based time slot management for high data rate WPAN MAC. The proposed medium access slot management scheme is performed using real time beacon parsing and time slot assignment for MAC superframe. It includes management information and scheduling method to guarantee real time characteristics for high speed MAC hardware. By adopting several hardware features, we can minimize the software intervention and maximize the overall system performance.