covidcotra

This is an experimental rust library for managing the data exchange for a covid-19 contract tracing system.

Concepts

Conceptionally there are three components:

• Identity represents a single device.
• Authority represents a trusted authority (for instance the ministry of health)
• ContactLog is a minimal abstraction over a contact log.

Identity

The identity internally holds a unique ID (the UniqueIdentity). This identity is only ever transmitted to the central authority when the person behind this identity tests positive.

An identity can be looked at in two other ways: a ShareIdentity which is an identity which is encrytped with the public key of the public authority and is only ever shared with other devices. The share ID should rotate regularly and can be used by the central authorities to determine that a user saw another user. Since the IDs rotate it's impossible (at least on this level) for a device to determine that they have seen a device a second time.

Secondarily there is the HashedIdentity. This is a hashed version of the unique ID which can be used to "poll" for updates or subscribe to a push channel. The central authority cannot map from hashed identity to unique identity but the other way round. This means that the unique identity (which eventually gets associated with a real human identity if revealed) only gets known to the central authority under the following circumstances:

• a user tests positive and reveals
• the central authority listens on device IDs walking around with a lot of devices deployed all over the place.
• a user submits a list of contacts they saw

When a user is revealed by testing positive they are encouraged to rotate the ID. Since other users unique IDs are also revealed through contact list uploaded they are encouraged to rotate once they are either tested positive themselves or tested negative.

This is a proof of concept for this blog post about contact tracing.

License: Apache-2.0