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=== pam_u2f ===
=== pam_u2f ===


The `pam_u2f` 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.  
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/
Use this page to check whether your Yubikey supports '''FIDO U2F''' before starting: https://www.yubico.com/products/identifying-your-yubikey/
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1. Connect your Yubikey
1. Connect your Yubikey


2. Create an authorization mapping file for your user. The authorization mapping file is like `~/.ssh/known_hosts` but for Yubikeys.
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>nix-shell -p pam_u2f</code>
# <code>mkdir -p ~/.config/Yubico</code>
# <code>mkdir -p ~/.config/Yubico</code>
# <code>pamu2fcfg > ~/.config/Yubico/u2f_keys</code>
# <code>pamu2fcfg > ~/.config/Yubico/u2f_keys</code>
# add another yubikey (optional): <code>pamu2fcfg -n >> ~/.config/Yubico/u2f_keys</code>


3. Verify that `~/.config/Yubico/u2f_keys` contains one line in the following style:
 
3. Verify that <code>~/.config/Yubico/u2f_keys</code> contains one line in the following style:


<syntaxHighlight>
<syntaxHighlight>
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PAM U2F Docs: https://developers.yubico.com/pam-u2f/  
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 ===
=== yubico-pam ===


The `yubico-pam` module uses a OTP (one time password) challenge response to authenticate users.
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/
Use this page to check whether your Yubikey supports '''Yubico OTP''' before starting: https://www.yubico.com/products/identifying-your-yubikey/


You can enable challenge-response logins with:
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>
 
{{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-manager</code>
# <code>ykman otp chalresp --touch --generate 2</code>
# <code>ykpamcfg -2 -v</code>




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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 ==
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* [https://rzetterberg.github.io/yubikey-gpg-nixos.html GPG-keys for SSH authentication on NixOS]
* [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]]
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