Although widely employed in mission-critical applications, Underwater Acoustic Networks (UANs) are intrinsically susceptible to Denial of Service (DoS) attacks, due to the broadcast nature of the underwater acoustic channel. These security breaches can severely compromise the UAN’s operational integrity and disrupt the overall network performance, requiring adequate safeguards to be put in place. Reputation-based trust systems represent one of the most effective countermeasures against these threats, protecting from a wide range of attacks by predicting the reliability of nodes’ future behavior based on historical evidence such as their level of participation in network communication. However, this type of communication-based trust evidence, collected by nodes about their 1-hop neighbors, often leads to wrong trust assessments caused by poor link quality that could be avoided by taking channel conditions into account and/or incorporating third-party reputation information when evaluating trustworthiness. In [1], a channel-based reputation system weighing observations based on channel state is presented. Work presented in [2] expands such system by employing Trust- Related Data (TRD) dissemination to make any node in a multihop UAN aware of the trustworthiness of each other. This paper is a substantial extension of [2], introducing first-hand and second-hand TRD integration and rendering the system suitable for deployment by minimizing the amount of transmitted data. Additionally, we present a more comprehensive simulationbased evaluation of the proposed security framework, including a performance analysis in a scenario involving a mobile node, tests against attacks targeting the reputation system itself (such as slandering and spoofing) and a real-world validation conducted through a dedicated sea trial.

This paper presents an analysis of data collected during sea trials, showcasing the capabilities of the buoy concept outlined in prior publication. Underwater networks that are extended through a wireless network domain can enhance an underwater network’s characteristics in terms of bandwidth, robustness, interoperability and distance. Central to the setup is a gateway buoy facilitating connectivity between the underwater network and the surface wireless network. Two distinct sets of measurements were conducted: one utilizing High Frequency (HF) and the other employing Long-Term Evolution (LTE) technology. The primary focus of these measurements is to assess the achievable range. The performance of these wireless technologies plays a crucial role in this analysis.

In this paper, we propose a concept, design, and implementation of a moored buoy, that is equipped with under-water and radio modems, allowing it to function as a gateway between land-based entities and the acoustic underwater network following the ISO/IEC Underwater-IoT architecture. Utilizing buoys as gateways offers the advantage of reduced noise interference, as they are not affected by engine noise that typically disturbs communication from ships. We highlight its performance improvements achieved by using a gateway buoy within an international sea trial with an acoustic network of 11 nodes. Besides the technology concept of a gateway buoy, we also present the routing adaptions made to the network protocol Gossiping in Underwater Mobile Ad-Hoc Networks (GUWMANET). These extensions allow routing between air-bound network participants and the underwater network, and partially routing underwater messages above the surface using multiple gateway buoys. This approach can increase the robustness and reduce the overall delay, due to the significantly faster propagation of electromagnetic waves compared to sound waves.

Underwater acoustic networks are often used in mission-critical scenarios, such as military underwater networks and assets deployed for tsunami prevention; hence, an attack performed against these types of networks can easily lead to disastrous consequences. Nevertheless, countermeasures to possible network attacks have not been widely investigated so far. A reputation system, where a node gains trust each time it exhibits a good behavior, and loses trust each time it behaves suspiciously, is an effective way to identify possible attackers in the network. The main challenge when applying a reputation system in an underwater network is to understand whether the network performance degrades because a node is acting maliciously intentionally, or because of the changed channel conditions, causing a large packet drop. For instance, when a ship travels close to an underwater network deployment, it causes an increased packet loss, and so does the change of environmental conditions, such as a drop of temperature, the presence of rain or the increase of the wind speed. This behavior of the acoustic channel can be characterized with a hidden Markov model, whose parameters are obtained observing the time evolution of the acoustic channel in a sea experiment. This article presents a trust model based on the knowledge of the channel state, inferred from the perceived noise and received signal strength, in which misbehavior and correct behavior are considered differently according to the actual channel state. We evaluate the model both analytically and through simulations, implementing the trust mechanism in the DESERT Underwater Network framework.

In this work, non-binary polar codes are investigated for input alphabets sizes being a prime number. The similarities and differences in the encoding and decoding process are shown with respect to binary polar codes. The performance of polar codes over GF(3) and GF(5) in combination with 3-PSK and 5-PSK is evaluated for short messages in comparison to binary polar codes with common phase shift keying constellations.

The performance of modern information systems in the hydrosphere is based on the robustness of the wireless underwater communication between the cooperative subsystems. It is strongly intertwined with the coordination reliability for sharing resources and common purposes. Secure underwater coordination is a key functionality (C4I-STAR). The physical laws of the nature restrict the band-width and reliability of underwater communication links, the quality differs from deep to shallow water areas, with the hydro acoustical parameters, like the sound speed and sediment profile, with the weather conditions and day time. To over-come low data rates and non robust transmission links of submerged manned and unmanned platforms, error tolerant processes are needed to fulfill different hand-over maneuvers in the submerged teams. But, what are efficient process chains in this field? S-BPM has advantages to support users and scientists to handle this layer modeling for a standard network code of conduct.