Universal 2nd Factor, or U2F, is an authentication standard developed by the FIDO Alliance that is designed to be open, secure, private, and easy to use. The U2F key plugs into your USB port and when tapped or when the button is pressed it sends a signed response back to Duo to validate your login.
At Andrews University, a U2F key is an alternative to the Duo security token and may be used by Andrews student employees as a second-factor authentication in instances when a phone or tablet is not a viable second-factor option device.
How does U2F work?
Fido Alliance
BLOG: Bringing U2F to the Masses
BLOG: Why 2018 will be the year for authentication hardware