Subject: [Ppm] Background: Exposure Notification Privacy-preserving Analytics (ENPA)

From: Charlie Harrison <[email-masked]>
Date: Fri, 29 Oct 2021 11:34:51 -0500

Hey folks,
I wanted to provide a bit more information about the Exposure Notification
[1] use-case and how it fits within the work described here. The Exposure
Notification System (ENS) is a decentralized mechanism for tracking
exposure to COVID-19, explicitly designed so no health authority has access
to the raw transmission data. This provides a challenge, as some amount of
data could be very useful to health authorities so long as it is
sufficiently private.

ENPA [2] was designed and deployed to solve this problem. It sits on top of
ENS and provides aggregate statistics using two-party computation based on
Prio [3], and anonymized with differential privacy. This ensures that no
health authority learns any one user’s data , but provides aggregate
statistics that are still useful. ENPA was designed and deployed by a
number of parties: Apple, Google, ISRG, MITRE, and NCI in NIH (also listed
in the FAQ listed in [2]).

I believe the network protocols underpinning ENPA are a good fit for PPM
standardization at IETF, with the cryptographic pieces (Prio) fitting in
CFRG.

[1] https://www.google.com/covid19/exposurenotifications/
[2]
https://github.com/google/exposure-notifications-android/blob/master/doc/enexpress-analytics-faq.md
&
https://github.com/google/exposure-notifications-android/blob/master/doc/ENPA.pdf
[3] https://crypto.stanford.edu/prio/