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Delivering confidential messages in wireless network is gaining continuous attraction as a fundamental building block for the Internet of things (IoT). This paper overviews the confidential message transmission techniques in broadcast channel (BC) where a transmitter serves multiple users by delivering confidential messages to their intended users. Each confidential message must be prevented from extracting its information by any unintended users. First, we consider a basic network consisting of two users. In the two-user BC, the secret dirty paper coding (S-DPC) achieves the secrecy capacity region. However, since the DPC requires a high computational complexity for characterizing the capacity region, two sub-optimal transmission techniques with low complexities are explained. Second, we extend our discussion to the network including more than two users. For $K$ -user BC with confidential messages, the optimal transmission scheme and the secrecy capacity region have not yet been derived. Instead of presenting the optimal scheme, we explain two sub-optimal transmission techniques and compare their features and performances. In conclusion, we discuss the open problems in the confidential message transmission for networks with more than two users.

In this paper, we investigate a secure cognitive radio network (CRN), which deploys non-orthogonal multiple access (NOMA) to deliver a mixed multicast and unicast traffic to the intended receivers, while keeping them secret from the eavesdroppers. This model represents a cognitive interference channel with an external eavesdropper (CIC-EE). In this model, there are one pair of primary nodes, one pair of secondary nodes, and an external eavesdropper. The primary transmitter multicasts a confidential message to both primary and secondary receivers, while trying to keep it secret from the eavesdropper. The secondary transmitter helps the primary user to deliver its message in exchange of transmission opportunity. The secondary message is unicasted to the secondary receiver, while concealing it from both primary receiver and the eavesdropper. This scenario models a NOMA-based overlay cognitive radio paradigm with an external eavesdropper. For this scenario, the achievable rate-equivocation region is obtained and its optimality is shown for a class of degraded channels. Then, the results obtained for the discrete memoryless channel are extended to the Gaussian channel model. Furthermore, by deploying numerical examples, a comparison is made between the proposed secure NOMA-based scheme, its orthogonal multiple access (OMA) based counterpart, and a cognitive interference channel without an external eavesdropper. It is shown that the NOMA-based method achieves significantly higher rates than its OMA based counterpart.

Wireless sensor networks (WSNs) consist of tiny sensor nodes distributed over a specific geographical area. Eavesdropping can be considered as an attack against WSNs when an adversary node overhears the transmissions among the sensor nodes. Hence a WSN needs to minimize the risk of overhearing in order to operate safely. One of the most important performance metrics of WSNs is network lifetime. Decreasing the transmission power levels of the nodes in order to reduce the overhearing can negatively affect the network lifetime due to the suboptimal routing paths that are used. In this study, two optimization models are developed to jointly reduce eavesdropping and increase the network lifetime. The analysis of the relationship between eavesdropping and network lifetime is investigated by using the proposed optimization models. As a result of this study, it was observed that the minimum reduction of eavesdropping causes a significant decrement in network lifetime and when the overhearing limit is extended to a certain level, the network lifetime converges to the maximum. © 2018 IEEE. Aselsan,et al.,Huawei,IEEE Signal Processing Society,IEEE Turkey Section,Netas