Wireless Sensor Networks, part 2: Limitations
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In Part I of the Wireless Sensor Networks (WSN) article, I discussed basic issues covering the sensors' network topology and hardware architecture, uses of WSN and issues that are still open for research. In this article, I will continue the discussion with two issues: the limitations that affect the efficient operation of WSN, particularly when implementing security techniques, and more challenges that need to be taken into consideration to build efficient WSN.
As explained in the first part of the WSN article, sensor networks are often used in mission critical environments such as in military and healthcare applications. As you can understand, these environments have demanding security requirements that must be addressed at the initial phase of design, in an attempt to focus on a spherical security strategy that will cover as many security problems as possible.
A number of security issues exist in WSN and need to be analyzed in detail in order to design appropriate security mechanisms and overcome security problems that arise in the sensor environment. However, designing new security protocols and mechanisms is constrained by the capabilities of the sensor nodes. This section discusses the limitations that complicate the security design and deployment in sensor networks. It is important to understand the constrained capabilities of sensor nodes if you wish to develop proper security that balances demanding security performance against sensor nodes' limitations.
1. Hostile Environment
Sensor networks can be deployed in remote or hostile environments such as battlefields. In these cases, the nodes cannot be protected from physical attacks, since anyone could have access to the location where they are deployed. An adversary could capture a sensor node or even introduce his own malicious nodes inside the network. If the latter is the case, the adversary’s aim is to trick the network into accepting his nodes as legitimates.
In either case, the adversary can compromise sensitive information, which is either stored on the compromised nodes or is forwarded through the adversary’s nodes to the next hop; the sensitive information that is collected could be used for illegal purposes. The challenge here for researchers and developers is to design resilient security protocols and solutions offering security, even if a subset of sensor nodes is compromised. It is important to ensure that, if a node is compromised, sensitive information stored on the node cannot be taken off with ease.
2. Random topology
Most of the time, deploying a sensor network in a hostile environment is done by random distribution, i.e. from an airplane. Therefore, it is difficult to know the topology of sensor networks a priori. In these situations, it is hard to store various encryption keys on nodes in order to establish encryption among a group of neighbors, since the neighborhood cannot be known a priori.
The challenge is to design key agreement protocols that do not require certain nodes to be neighbors of some other nodes, and also do not require encryption keys to be stored on sensors before deployment. Appropriate key distribution algorithms must be designed along a flexible WSN architecture to securely provide encryption keys in real time.
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