Due to the sensitive and often personal nature of sensor data that many wireless sensor networks collect, the security of this data must be guaranteed. This is fast becoming an important concern for sensor networks which are finding applications in the military and home health domains. The best and often the only way to secure this data is to encrypt it using a secure encryption algorithm before it is transmitted over the air ways. Due to the constrained nature of the resources, memory and clock speeds, available on sensor nodes however, the cost, both in terms of power consumption and speed of encryption, of a software based encryption procedure can often outweigh the risks of the transmission being intercepted. This paper presents a solution to reduce this cost of employing encryption by taking advantage of a resource already available on many sensor nodes, including the Crossbow MICAz and MoteIV's TmoteSKY; this resource being the AES encryption module available on the Chipcon CC2420 transceiver chip. The performance of using this method of securing data on a sensor network against using software implementations of some of the most popular cipher algorithms suitable for WSN is then analysed for both hardware platforms. © 2008 Springer-Verlag Berlin Heidelberg.