Wearable technology is increasingly being used for medical applications such as continuous monitoring of chronically ill patients in homes and hospitals. The various stakeholders (patients, doctors, insurers) have an interest in ensuring not only that the data is untampered, but also that the context is verifiable (e.g., correct time and location can be associated with the data collected). Prior works have studied these aspects in isolation, typically using cryptographic techniques. In this paper, we develop a new solution that leverages the density of wireless devices in the vicinity of the transaction to create witness records ensuring data is tamper-protected and bound to its time and location context. Our first contribution is to develop a secure logging architecture that compacts witness records using Bloom filters and hash-chains them to bind them to the data, allowing fast and reliable forensic verification. Our second contribution is to identify the various configuration parameters influencing the performance of our scheme in terms of storage, processing, and transmission efficiency, and to quantify their effect on verification accuracy. Our third contribution implements and demonstrates the feasibility of our scheme, and quantifies its efficacy via simulation using real trace data from a multi-storey building representing a hospital environment.

The use of wearable devices, such as smartwatches, glasses, clothes, and fitness bracelets is increasing at an ever-growing pace. Major corporations and insurance companies have started mandating their use for their employees and clients. Data from such devices have begun to feature in settlement claims and as evidence in courts as well, requiring it to be irrefutable and tamper-proof. Lack of protection for personal data as well as the contextual information such as location tracking and its use by law enforcement agencies is raising serious privacy concerns among the general public and civil liberty advocates. In this article, we propose a novel scheme to secure the wearable sensor's communication through its crowdsourced logging by neighboring wearable and smart devices called witnesses preserving the contextual information (such as time and location) as well. To ensure witness privacy, gateway and witness devices use the reciprocity property of wireless medium between them to generate pairs of closely matching link signatures, which not only provide the proof of presence for the witnesses in the vicinity but also act as their time-varying pseudonyms. We demonstrate the feasibility and efficacy of our scheme through the prototype implementation using real wireless devices, and via simulation and experimental results.