What is a physical security key? How does a physical security key work?

A security key is a hardware authentication device used to protect access to computers, networks, and online systems that supports one-time passwords, public-key cryptography, and authentication.

Typically, you insert the security key into your device (or wirelessly connect it) and press a button on the key itself. The security key will then be presented with a challenge by your web browser. It will cryptographically sign this challenge, verifying your identity and whatever it is you're trying to access.

You can use a physical security key to authenticate into almost any system, but you should use a dedicated one for the Internet Identity and authorize as many other devices as possible. Ideally, you’ll want to purchase a security key that supports Fido U2F and can communicate with both your phone and your computer.