The YubiKey 4 is a multi-purpose USB key produced by Yubico.

It can be used for 2-factor authentication (OTP, U2F, OATH and static password) and as a CCID smartcard (both PIV and OpenPGP), visit the Yubico product page for a full list of features and a comparison with previous versions.

udev

Up to jessie, to use the card as a non-root users, you need to add a line to /etc/udev/rules.d/99-yubikeys.rules to the tell udev either

• to give permissions to the plugdev group

# YubiKey 4 OTP+U2F+CCID
SUBSYSTEMS=="usb", ATTRS{idVendor}=="1050", ATTRS{idProduct}=="0407", GROUP="plugdev"

• to let systemd-logind (thanks to Sam Morris via Iaian Learmoth) adding the ACLs for the console user

# YubiKey 4 OTP+U2F+CCID
SUBSYSTEMS=="usb", ATTRS{idVendor}=="1050", ATTRS{idProduct}=="0407", TAG+="uaccess"

By default, an even better configuration would be to merge the two lines:

# YubiKey 4 OTP+U2F+CCID
SUBSYSTEMS=="usb", ATTRS{idVendor}=="1050", ATTRS{idProduct}=="0407", GROUP="plugdev", TAG+="uaccess"

Configuration

Yubico develops various software to access the key, among them:

• YubiKey Personalization to configure all the 2-factor authentication protocols

  • you need at least the version in stretch, i.e. 1.17.2-1

• Yubico PIV (Privilege and Identification Verification) for PKCS #11

OTP

The key does not have a battery, so for TOTP you need an external tools:

• yubikey-totp to generate a TOTP code from a secret stored on the key.

  • you need at least the version in stretch, i.e. 1.3.1-1

• Yubico Authenticator to generate OATH-HOTP and OATH-TOTP one-time password codes from secretes protected by the key

PIV

Check also Debian SSO (Single Sign-On) with a YubiKey.

OpenPGP

Links

Various interesting HowTo, especially useful if you are new to OpenPGP subkeys:

• https://blog.josefsson.org/2014/06/23/offline-gnupg-master-key-and-subkeys-on-yubikey-neo-smartcard/

• https://www.sidorenko.io/blog/2014/11/04/yubikey-slash-openpgp-smartcards-for-newbies/

• https://anarc.at/blog/2015-12-14-yubikey-howto/

• https://iain.learmonth.me/yubikey-neo-gpg/

Needed packages

To access the card you need GnuPG, the version in wheezy is fine for signing/encrypting.

However, if you want to use 4096-bits RSA keys, you need GnuPG 2.x, with the corresponding gpg-agent and scdaemon, at least the version in wheezy-backports, i.e. 2.0.25-1~bpo70+1.

GNOME Keyring

Please note that you need at least gnome-keyring 3.16.0-3 which disables the internal gpg-agent and relies on pinentry-gnome/gnupg-agent instead, see 773304.

For previous gnome-keyring versions, you should manually disables the internal gpg-agent and ssh-agent (if needed), see 623539:

$ mkdir -p ~/.config/autostart
$ echo 'X-GNOME-Autostart-enabled=false' \
  | cat /etc/xdg/autostart/gnome-keyring-gpg.desktop - \
  >>~/.config/autostart/gnome-keyring-gpg.desktop
$ echo 'X-GNOME-Autostart-enabled=false' \
  | cat /etc/xdg/autostart/gnome-keyring-ssh.desktop - \
  >>~/.config/autostart/gnome-keyring-ssh.desktop

OpenSSH authentication

This works out-of-the box on wheezy with GnuPG Agent and the corresponding scdaemon. You need to configure:

• GnuPG to use the agent, in ~/.gnupg/gpg.conf

use-agent

• GnuPG Agent to also act as an SSH agent, in ~/.gnupg/gpg-agent.conf:

enable-ssh-support

Once the agent started and the key plugged in, you can check if its authentication key has been added to the agent via the ssh-add -l command and then export the public key via the ssh-add -L command.

However, if you use GNOME Keyring, read this note.

License

This document is licensed under the terms of the GNU General Public License (GPL), version 2 or (at your option) any later version.

• CategoryHardware