Passkeys and Fido2: Security, Usability and Deployment of Passwordless Authentication

Passwords have outlasted two decades of schemes proposed to replace them, and the reasons are well documented. FIDO2 pairs a browser interface, WebAuthn, with a client-to-authenticator protocol, CTAP. It is supported by virtually every browser and by the major operating systems, and its credentials are now called passkeys. This review reads the peer-reviewed literature on it. We describe how a signature bound to the web origin defeats phishing, then set out what formal analyses have proved and under which assumptions. We go through the attacks published so far: a social-engineering downgrade to weaker fallback methods, a side channel on a hardware token, a timing leak that links accounts, and weak configuration on live websites. User studies and reports from organisations are compared. One finding recurs across these strands. The cryptographic core holds up, and the trouble sits at the edges, in fallback methods, account recovery and credentials synchronised through a provider account. This is a review of published work. No new experiment is reported, and the two diagrams are schematic.