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This article describes how you can integrate [https://yubico.com Yubico]'s [[Wikipedia:YubiKey|YubiKey]] with NixOS.
This article describes how you can integrate [https://yubico.com Yubico]'s [[Wikipedia:YubiKey|YubiKey]] with NixOS.


== For GPG and SSH  ==
== GPG and SSH  ==


Based on [https://github.com/drduh/YubiKey-Guide a guide] by [https://github.com/drduh @drduh]:
Based on [https://github.com/drduh/YubiKey-Guide a guide] by [https://github.com/drduh @drduh]:
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services.udev.packages = [ pkgs.yubikey-personalization ];
services.udev.packages = [ pkgs.yubikey-personalization ];


# Depending on the details of your configuration, this section might be necessary or not;
programs.gnupg.agent = {
# feel free to experiment
   enable = true;
environment.shellInit = ''
   enableSSHSupport = true;
   export GPG_TTY="$(tty)"
};
   gpg-connect-agent /bye
</syntaxHighlight>
  export SSH_AUTH_SOCK="/run/user/$UID/gnupg/S.gpg-agent.ssh"
 
'';
== Logging-in ==


programs = {
To use your yubikey as a user login or for sudo access you'll have to install a PAM (Pluggable Authentication Module) for your yubikey.
  ssh.startAgent = false;
 
  gnupg.agent = {
=== pam_u2f ===
    enable = true;
 
    enableSSHSupport = true;
The <code>pam_u2f</code> module implements the U2F (universal second factor) protocol. The protocol was initially developed by Yubico, Google and NXP and is nowadays hosted as an open-standard by the FIDO Alliance. All current and most legacy Yubikeys support the U2F protocol making this the preferred way to use Yubikeys for user login.
  };
 
};
Use this page to check whether your Yubikey supports '''FIDO U2F''' before starting: https://www.yubico.com/products/identifying-your-yubikey/
 
1. Connect your Yubikey
 
2. Create an authorization mapping file for your user. The authorization mapping file is like <code>~/.ssh/known_hosts</code> but for Yubikeys.
 
# <code>nix-shell -p pam_u2f</code>
# <code>mkdir -p ~/.config/Yubico</code>
# <code>pamu2fcfg > ~/.config/Yubico/u2f_keys</code>
# add another yubikey (optional): <code>pamu2fcfg -n >> ~/.config/Yubico/u2f_keys</code>
 
 
3. Verify that <code>~/.config/Yubico/u2f_keys</code> contains one line in the following style:
 
<syntaxHighlight>
<username>:<KeyHandle1>,<UserKey1>,<CoseType1>,<Options1>:<KeyHandle2>,<UserKey2>,<CoseType2>,<Options2>:...
</syntaxHighlight>
</syntaxHighlight>


If you don't have a graphical user interface, you'll have to adjust the pinentry program (it's the program launched by operating system to ask for YubiKey's PIN):
4. Enable the u2f PAM module for login and sudo requests


<syntaxHighlight lang=nix>
<syntaxHighlight lang=nix>
programs.gnupg.agent.pinentryFlavor = "curses";
security.pam.services = {
  login.u2fAuth = true;
  sudo.u2fAuth = true;
};
</syntaxHighlight>
</syntaxHighlight>


== Logging-in ==
PAM U2F Docs: https://developers.yubico.com/pam-u2f/
 
 
5. Verify PAM configuration
 
See chapter ''Test PAM configuration'' an the end of this page.
 
=== yubico-pam ===
 
The <code>yubico-pam</code> module uses a OTP (one time password) challenge response to authenticate users.
 
Use this page to check whether your Yubikey supports '''Yubico OTP''' before starting: https://www.yubico.com/products/identifying-your-yubikey/
 
You'll first need to install the necessary udev packages to your NixOS configuration:<syntaxhighlight lang="nix">
services.udev.packages = [ pkgs.yubikey-personalization ];
</syntaxhighlight>You can program the Yubikey for challenge-response on slot 2 and setup the current user for logon:
# <code>nix-shell -p yubico-pam -p yubikey-manager</code>
# <code>ykman otp chalresp --touch --generate 2</code>
# <code>ykpamcfg -2 -v</code>
Finally, you can enable challenge-response logins with the following commands:
 
'''1.)'''
run: <code>nix-shell --command 'ykinfo -s' -p yubikey-personalization</code>
to get the serial code and enter it into <code>yubico.id = [ "12345678" ];</code>


You can enable challenge-response logins with:
{{warning|1=Ignoring step 1 is considered insecure, any user could just plugin a yubikey and gain root access!}}


<syntaxHighlight lang=nix>
'''2.)'''<syntaxHighlight lang=nix>
security.pam.yubico = {                                                                                                                                                                                                                                              
security.pam.yubico = {
   enable = true;                                                                                                    
   enable = true;
   debug = true;                                                                                                      
   debug = true;
   mode = "challenge-response";                                                                                      
   mode = "challenge-response";
};
  id = [ "12345678" ];
};
</syntaxHighlight>
</syntaxHighlight>


You'll also need to program the Yubikey for challenge-response on slot 2 and setup the current user for logon:


# <code>nix-shell -p yubico-pam -p yubikey-personalization</code>
To automatically login, without having to touch the key, omit the <code>--touch</code> option.
# <code>ykpersonalize -2 -ochal-resp -ochal-hmac -ohmac-lt64 -oserial-api-visible</code>
# <code>ykpamcfg -2 -v</code>


Having that, you should be able to use your Yubikey to login and for sudo. You can also set <code>security.pam.yubico.control</code> to "required" in order to have multi-factor authentication.
Having that, you should be able to use your Yubikey to login and for sudo. You can also set <code>security.pam.yubico.control</code> to "required" in order to have multi-factor authentication.
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</syntaxHighlight>
</syntaxHighlight>


Please note that the PCSC-Lite daemon [https://ludovicrousseau.blogspot.com/2019/06/gnupg-and-pcsc-conflicts.html sometimes conflicts] with gpg-agent.
Please note that the PCSC-Lite daemon [https://ludovicrousseau.blogspot.com/2019/06/gnupg-and-pcsc-conflicts.html sometimes conflicts] with gpg-agent. This can be solved by putting the line <code>disable-ccid</code> into <code>~/.gnupg/scdaemon.conf</code>. There is also a [https://nix-community.github.io/home-manager/options.xhtml#opt-programs.gpg.scdaemonSettings Home Manager Option] for that.


== OTP ==
== OTP ==


In order to manage OTP keys, you should install the <code>yubioath-desktop</code> package in your profile.
In order to manage OTP keys, you should install the <code>yubioath-flutter</code> package in your profile.
This application will also require both the udev rules as well as pcscd enabled.
This application will also require both the udev rules as well as pcscd enabled.


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It is best practice to create the keys on a system without network connection to avoid leakages.
It is best practice to create the keys on a system without network connection to avoid leakages.
This [https://github.com/drduh/YubiKey-Guide guide] explains in depth the steps needed for that.
This [https://github.com/drduh/YubiKey-Guide guide] explains in depth the steps needed for that.
There is also a [https://github.com/Mic92/dotfiles/blob/a41e9c1722f7e81af21741ea75ced9ceff46230e/nixos/images/yubikey-image.nix nix expression] that creates a nixos live image with all necessary dependencies pre-installed.
There is also a [https://github.com/Mic92/dotfiles/blob/ed0ac1af816a7ebb7c5d4f040b77fa88e3ec1c79/nixos/images/yubikey-image.nix nix expression] that creates a nixos live image with all necessary dependencies pre-installed.
The image can be created with the [https://github.com/nix-community/nixos-generators nixos-generator tool]
The image can be created with the [https://github.com/nix-community/nixos-generators nixos-generator tool]
and depending on the image copied onto a usb stick or executed directly using <code>kexec</code>
and depending on the image copied onto a usb stick or executed directly using <code>kexec</code>
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# Plug in the new YubiKey
# Plug in the new YubiKey
# <code>gpg --card-status</code> (optional, to see if key is visibile)
# <code>gpg --card-status</code> (optional, to see if key is visibile)
== Test PAM configuration ==
Test user and/or sudo authentication.
Replace <code><username></code> by your users account name.
# <code>nix-shell -p pamtester</code>
# <code>pamtester login <username> authenticate</code>
# <code>pamtester sudo <username> authenticate</code>
If the result is <code>pamtester: successfully authenticated</code> then everything should work as expected.
== Locking the screen when a Yubikey is unplugged ==
This can be achieved with a <code>udev</code> rule, which can be added to your <code>configuration.nix</code>
<syntaxHighlight lang=nix>
services.udev.extraRules = ''
      ACTION=="remove",\
      ENV{ID_BUS}=="usb",\
      ENV{ID_MODEL_ID}=="0407",\
      ENV{ID_VENDOR_ID}=="1050",\
      ENV{ID_VENDOR}=="Yubico",\
      RUN+="${pkgs.systemd}/bin/loginctl lock-sessions"
  '';
</syntaxHighlight>
This will lock all sessions if any Yubikey matching the rule is unplugged.
If this does not work with your Yubikey take a look at the output of this command when you plug-in/unplug your Yubikey
<code>udevadm monitor --udev --environment</code> and adjust the rule accordingly. This rule should work with most Yubikey 5 series models


== Links ==
== Links ==


* [https://rzetterberg.github.io/yubikey-gpg-nixos.html GPG-keys for SSH authentication on NixOS]
* [[Yubikey_based_Full_Disk_Encryption_(FDE)_on_NixOS]]
* [[Yubikey_based_Full_Disk_Encryption_(FDE)_on_NixOS]]
[[Category:Cookbook]]
[[Category:Security]]
[[Category:Hardware]]
Retrieved from "https://wiki.nixos.org/wiki/Yubikey"