UAF / U2F
FIDO uses two main security protocols: Universal Authentication Framework (UAF) and Universal Second Factor (U2F).
UAF works as a site’s primary security mechanism, uniting multiple forms of authentication under one set of protocols.
U2F is designed to augment a site’s current security measures. Users present a USB or near-field communication device — something found in many smartphones — to double-check the credentials they’ve already entered.