Overview

This pull request adds support for YubiKey, a USB authentication device commonly used for 2FA. Support is added by configuring a YubiKey slot to operate in HMAC-SHA1 challenge-response mode. The mechanism works by submitting the database master seed as a challenge to the YubiKey which replies with a HMAC-SHA1 cryptographic hash. The resultant hash is then hashed with the other keys (password, keyfile) to generate the final key used to encrypt the database.

I have uploaded a few screenshots t...