Wearable sensors for heart-rate, ECG, blood pressure, and blood glucose are gaining increasing prominence in home-based healthcare. Though the medical sensory data is now routinely encrypted and signed, the timestamp associated with the data, which is needed for accurate correlation and reconstruction of medical events, remains poorly secured. In this paper we first motivate the problem by demonstrating with two medically approved devices on the market today that timestamps can be easily tampered to backfill medical data. We then propose a novel solution that works within the resource constraints of wearable devices to secure timestamps against malicious or ill-configured gateways. Lastly, we evaluate our solution via simulation and experimentation across multiple network access technologies.
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