Some systems require users to provide verification of their identities to log in. This is usually done with passwords that serve as a security key. Google, Dropbox, GitHub and other major sites have implemented it to some degree. Google has tried using a USB device called Security Key to help it go down the dongle-style cryptographic path without incurring the overhead of smartcard readers or drivers. The Security Key generates a cryptographic assertion, which is used for the additional authentication.”]
Source: https://securityintelligence.com/news/google-is-ga-ga-over-security-key/