The Implementation of the Method Used in the NHSX App

The NHSX Contact Tracing App uses ECIES to send Bob’s identifier to the Health Authority (HA). Initially the HA creates a unique InstallationID for Bob, and sends their public key (PubHA). Bob then creates a new key pair every day (PubBobD, PrivBobD). Bob then creates a secret Z using the HA’s public key and Bob’s daily private key. This is then used to create an AES encryption key in order to…