  Medical data belongs to whom it produces it. In an increasing manner, this
data is usually processed in unauthorized third-party clouds that should never
have the opportunity to access it. Moreover, recent data protection regulations
(e.g., GDPR) pave the way towards the development of privacy-preserving
processing techniques. In this paper, we present a proof of concept of a
streaming IoT architecture that securely processes cardiac data in the cloud
combining trusted hardware and Spark. The additional security guarantees come
with no changes to the application's code in the server. We tested the system
with a database containing ECGs from wearable devices comprised of 8 healthy
males performing a standarized range of in-lab physisical activities (e.g.,
run, walk, bike). We show that, when compared with standard Spark Streaming,
the addition of privacy comes at the cost of doubling the execution time.
