Secret Key Generation for Body-Wearable Wireless Sensor Devices

The last decade has witnessed a rapid surge in application of body sensor net-works, especially in the domains of military, healthcare and fitness. In suchnetworks, wearable wireless sensor devices are used to measure and communi-cate a subject’s vital signs (such as heart rate, body temperature, blood glucoselevel, etc.) Security, in this context, is a critical issue as these devices deal withpersonal health data, requiring strict privacy and confidentiality. However, tra-ditional secret-key generation mechanisms (such as Diffie-Hellman) are typicallycomputation and power intensive and not suitable for resource-constrained sen-sor devices. This thesis aims at realizing a practical and low-cost secret keygeneration mechanism for wearable sensor devices.First, we investigate a secret key generation mechanism that extracts sharedsecret keys using properties of the near-body wireless channel between two com-municating parties. For a fully body-worn scenario, our experimental results,using off-the-shelf IEEE 802.15.4 devices, indicate that this approach is feasiblefor dynamic scenarios where communicating devices are placed in non-line-of-sight positions on the body. We also suggest an enhancement for existing keygeneration mechanisms using a filtering mechanism which considerably reducesbit mismatches.Second, we employ a channel hopping technique to decorrelate secret bit ex-traction. Due to fast sampling rates, successive samples of channel properties arecorrelated in time, yielding weak keys with reduced entropy. To overcome this, weuse channel hopping to increase channel diversity. We conduct extensive experi-ments to show that channel hopping increases frequency diversity and effectivelydecorrelates successive channel samples and thereby dramatically improving thestrength of the secret key. Furthermore, we identify key parameters affectingperformance, namely channel spacing, the number of available channels, and useractivity. We show that it is possible to dev