FIDO2 Project

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A FIDO2 security key by Yubico

The FIDO2 Project is a joint effort between the FIDO Alliance and the World Wide Web Consortium (W3C) whose goal is to create strong authentication for the web. At its core, FIDO2 consists of the W3C Web Authentication (WebAuthn) standard and the FIDO Client to Authenticator Protocol 2 (CTAP2).[1] FIDO2 is based upon previous work done by the FIDO Alliance, in particular the Universal 2nd Factor (U2F) authentication standard.

Taken together, WebAuthn and CTAP specify a standard authentication protocol[2] where the protocol endpoints consist of a user-controlled cryptographic authenticator (such as a smartphone or a hardware security key) and a WebAuthn Relying Party (also called a FIDO2 server). A web user agent (i.e., a web browser) together with a WebAuthn client form an intermediary between the authenticator and the relying party. A single WebAuthn client Device may support multiple WebAuthn clients. For example, a laptop may support multiple clients, one for each conforming user agent running on the laptop. A conforming user agent implements the WebAuthn JavaScript API.

As its name implies, the Client to Authenticator Protocol (CTAP) enables a conforming cryptographic authenticator to interoperate with a WebAuthn client. The CTAP specification refers to two protocol versions called CTAP1/U2F and CTAP2.[3] An authenticator that implements one of these protocols is typically referred to as a U2F authenticator or a FIDO2 authenticator, respectively. A FIDO2 authenticator that also implements the CTAP1/U2F protocol so it is backward compatible with U2F.

The invention of using a smartphone as a cryptographic authenticator on a computer network is claimed in US Patent 7,366,913 filed in 2002.[4]


  1. ^ "FIDO2: Moving the World Beyond Passwords". FIDO Alliance. Retrieved 30 January 2019.
  2. ^ Balfanz, Dirk; Czeskis, Alexei; Hodges, Jeff; Jones, J.C.; Jones, Michael B.; Kumar, Akshay; Liao, Angelo; Lindemann, Rolf; Lundberg, Emil (eds.). "Web Authentication: An API for accessing Public Key Credentials Level 1". World Wide Web Consortium (W3C). Retrieved 30 January 2019.
  3. ^ Brand, Christiaan; Czeskis, Alexei; Ehrensvärd, Jakob; Jones, Michael B.; Kumar, Akshay; Lindemann, Rolf; Powers, Adam; Verrept, Johan, eds. (February 27, 2018). "Client to Authenticator Protocol (CTAP)". FIDO Alliance. Retrieved 30 January 2019.
  4. ^ US Patent 7,366,913