Consideration of security in telehealth wireless sensor network monitoring systems

Wireless sensor networks (WSNs) provide the potential for effective and cost efficient remote and ubiquitous health care monitoring as they are easy to install, robust and secure. By their nature, these WSNs use asynchronous communications to reduce transmission power and improve efficiency. However this form of communication creates potential issues with the synchronization of the data received and stored by the telehealth system that they provide data to. This problem can be exacerbated if multiple sensors are employed, which is very likely due to the relatively low cost of such devices as well as the intended applications of these WSNs. Time synchronization is one essential component to maintain in the security of data transmission through wireless sensor networks (WSN). Each individual node in a WSN contains a crystal clock. Although the natural frequency of each crystal clock remains relatively constant, the quality of the crystal and environmental factors such as temperature cause the frequency to drift over time. In order to ensure that each node maintains and broadcasts the same global time within the micro-second range, a time synchronization protocol must be implemented. Several protocols have been developed; however, none has been developed with security in mind. It is easy for a system error or even a malicious third party to compromise a node, causing faulty time sync messages to be sent into the network. The Flooding Time Synchronization Protocol (FTSP) [5] is proposed to ensure time sychrony in the telehealh WSN. The FTSP is made up of several component modules written in nesC and has been implemented in the TinyOS [1] environment. TinyOS is an open source operating system developed specifically for network systems. In order to investigate the effects of injecting bad time synchronization messages into a WSN implemented with the FTSP, one or two nodes in a testbed of Telos motes (a mote being a remote wireless sensor) have been programmed to send faulty time sync messages. In order to determine the level of security of the FTSP, the resulting global time errors are recorded and evaluated.