# Challenges, Threats, Security Issues and New Trends of Underwater Wireless Sensor Networks
## 3 Threats and Challenges in Underwater Wireless Sensor Networks (UWSNs)
### Active Attacks  
Active attacks refer to the attacks that attempt to alter, inject, delete or destroy the data transmitted in the network. Active attacks may intercept network data, and even worse, attempt to modify or drop packets to disrupt the communication and the operation of the network. Active attacks can be executed by internal or external malicious attackers. If the attacks are carried out by nodes that do not belong to the network, these kind of attacks are external attacks, which would be easier to detect and defend. Otherwise, if attacks come from an insider node, these kind of attacks are internal attacks, which can cause considerable damage to the network. It is unfeasible to detect a malicious node which is disguised as a normal node and then prevent it from disrupting the network. Even worse, internal attacks may be launched by compromised nodes which are actually legitimate nodes before being compromised. The compromised node has legitimate ID and other privacy data (e.g., secret key, encryption algorithm, trust value), which would act as a legitimate node and cause continuous attacks. From the analyses above, it is obvious that internal attacks are more difficult to detect and may cause more severe damages than external attacks. To prevent this problem, the feasible solution is using security mechanisms such as encryption, authentication and trust management. These security mechanisms suitable for UWSNs will be described in more detail in Section 4. According to the intention of attacks, active attacks can be classified in the following categories: node compromise attacks, repudiation attacks, packet-oriented attacks, protocol-oriented attacks, and denial of service (Dos) attacks [14]. * _Node compromise attacks_: a malicious attacker can tamper with underwater sensor nodes physically. As discussed in Section 2, in some specific fields of applications, underwater sensor nodes may be deployed in unattended and even worse hostile sea regions. Moreover, the network may consist of tens or hundreds of nodes deployed in large scales, which means that it is unable to ensure the safety of all nodes. An attacker can locate the nodes by monitoring the intensity of the acoustic signal and capture them. Worse, if there are no hardware hack-proof technique or other security mechanism, the attacker may easily crack and compromise them to read privacy data (e.g., secret key, encryption algorithm, trust value) and modify these data from internal memory. Moreover, the compromised node may be injected into the network as a legitimate node to monitor or cause continuous attacks. Therefore, in the vast majority of cases, the node compromise attacks are combined with other active attacks to cause more severe damage to disturb communication and cooperation between sensor nodes. To prevent network from these attacks, hardware hack-proof techniques, re-configuring, and trust management mechanisms should be designed and used for UWSNs. * _Repudiation attacks_: in repudiation attacks, malicious nodes deny having any involvement in particular action or communication with other nodes. This refers to the denial by a node involved in a communication of having participated in all or part of the communication, regardless whether that communication is malicious or not. * _Packet-oriented attacks_: in packet-oriented attacks, the malicious adversary lunches attacks that aiming at disrupt packet transmission or destroy the data of the packet. There are some common active attacks including: interception attack, modification attack, and injection attack. An interception attack is to capture packets from an acoustic channel by intercepting. Moreover, the attacker can read and modify the content of the intercepted packets which is called a modification attack. An injection attack is to inject useless or harmful packets into the network to consume nodes' energy or disrupt the network. * _Protocol-oriented attacks_: the malicious adversary launches attacks that aiming at disrupt the function of some specific protocols.