USB MFA security keys are physical authentication devices that provide an additional layer of security beyond traditional passwords. They work using cryptographic protocols and by requiring the user to physically interact with the device in order to verify their identity.
FIDO, which stands for Fast IDentity Online, is a set of authentication standards aimed at strengthening the user login process to online services. The standards are developed by the FIDO Alliance and promote faster, more secure authentication processes with the overall goal of eliminating password-based logins altogether.