Physical layer security (PLS), as a key technology for ensuring communication security, is widely applied in both point-to-point and multi-user communication scenarios due to its low computational and communicational overhead. However, executing physical layer security in underwater acoustic sensor networks (UASNs) poses considerable challenges in multi-user scenarios where hybrid attackers are present. To enhance the security performance of OFDMA based UASNs, we first model the secrecy capacity under the scenario of hybrid attackers. Then a joint subcarrier and power allocation algorithm named MWOM to maximize the total secrecy capacity of multiple users is proposed. In addition, an overlapping window-based dynamic clustering scheme is applied to reduce the feedback delay of the communication link. Finally, to reduce the complexity of the proposed allocation algorithm, we map the resource allocation problem to a bipartite graph model and derive the sub-optimal solution of the problem by leveraging graph theory. Simulation results verify that the proposed algorithm outperforms conventional algorithms in security performance, with negligible impact on communication performance. More importantly, we conducted actual sea trials in real underwater environments, which consistently confirmed these results.

Physical-layer-based key generation is a promising technique for enhancing the security of underwater acoustic sensor networks (UASNs) and has been widely studied in point-to-point scenarios. However, when it is extended to multiuser scenarios in UASNs, its overhead costs are high and the information transmitted is prone to leakage. In this study, a group key generation scheme called STO-GSKG is proposed to share a secret key for multiple users. The pairwise keys extracted from the acoustic channels between the cluster head and the member nodes are used to protect the distribution of group keys. Specifically, to reduce the time consumption and communication overhead required for probing channels, a spatial-temporal reuse-based channel probing method that exploits large delays of underwater acoustic (UWA) channels is proposed. Then, secret bit sequences with high consistency and strong randomness are generated using a joint design that utilizes the multipath characteristics of UWA channels and introduces time-varying channel obfuscation information. The performance of the proposed scheme is evaluated through simulation and field experiments. The results show that the STO-GSKG scheme is more effective and robust than existing methods.

This paper presents a joint beamforming scheme for secure communication in cognitive hybrid satellite- terrestrial network (HSTN). In this network, a multibeam satellite communication network termed as the primary network under the intercept of an eavesdropper shares spectrum with a terrestrial network termed as the secondary network. Specifically by considering that the powers of both the primary and secondary transmitters are limited to the certain values, we aim to maximize the secrecy rate for the primary user (PU), while the quality- of-service (QoS) of the secondary user (SU) is satisfied, and set up a constrained optimization problem. Since the optimization problem is nonconvex and its solution is very difficult to be obtained, we propose a reformulation technique to convert the objective function into a second order cone constrain. Thus, standard numerical packages and randomization techniques can be used to calculate the beamforming (BF) vectors of the satellite and base station (BS). Simulation results are provided to verify that with joint BF algorithm, the network can maintain a sufficient QoS of the SU, while providing high secrecy rate of the PU.