- https://developers.yubico.com/PGP/SSH_authentication/
- https://developers.yubico.com/PGP/
- https://www.sidorenko.io/blog/2014/11/04/yubikey-slash-openpgp-smartcards-for-newbies/
- http://stafwag.github.io/blog/blog/2015/06/16/using-yubikey-neo-as-gpg-smartcard-for-ssh-authentication/
- https://developers.yubico.com/PGP/Importing_keys.html