  This document presents an evolution of the ROBERT protocol that decentralizes
most of its operations on the mobile devices. DESIRE is based on the same
architecture than ROBERT but implements major privacy improvements. In
particular, it introduces the concept of Private Encounter Tokens, that are
secret and cryptographically generated, to encode encounters. In the DESIRE
protocol, the temporary Identifiers that are broadcast on the Bluetooth
interfaces are generated by the mobile devices providing more control to the
users about which ones to disclose. The role of the server is merely to match
PETs generated by diagnosed users with the PETs provided by requesting users.
It stores minimal pseudonymous data. Finally, all data that are stored on the
server are encrypted using keys that are stored on the mobile devices,
protecting against data breach on the server. All these modifications improve
the privacy of the scheme against malicious users and authority. However, as in
the first version of ROBERT, risk scores and notifications are still managed
and controlled by the server of the health authority, which provides high
robustness, flexibility, and efficacy.
