Universal 2nd Factor Authentication (U2F)

Universal 2nd Factor (U2F) is an open authentication standard that strengthens and simplifies two-factor authentication using specialized USB or NFC devices.

LLNG can propose to users to register their keys. When done, 2F registered users can not login without using their key.


Since February 2022, U2F is considered to be deprecated in Chrome and its derivatives. Administrators must migrate to WebAuthn instead. U2F security keys are compatible with WebAuthn but require a migration step to be performed in LemonLDAP::NG.

Prerequisites and dependencies

This feature uses Crypt::U2F::Server::Simple.

It is available as package on Debian:

apt install libcrypt-u2f-server-perl

For other systems, use CPAN. Before compiling it, you must install Yubico’s C library headers.


An HTTPS portal is required to use U2F


In the manager (second factors), you just have to enable it:

  • Activation: set it to “on”

  • Self registration: set it to “on” if users are authorized to register their keys

  • Allow users to remove U2F key: If enabled, users can unregister enrolled U2F device

  • Authentication level: you can overwrite here auth level for U2F registered users. Leave it blank keeps auth level provided by first authentication module (default: 2 for user/password based modules). It is recommended to set an higher value here if you want to give access to some apps only for enrolled users

  • Label (Optional): label that should be displayed to the user on the choice screen

  • Logo (Optional): logo file (in static/<skin> directory)

  • Lifetime (Optional): Unlimited by default. Set a Time To Live in seconds. TTL is checked at each login process if set. If TTL is expired, relative 2F device is removed.


If you want to use a custom rule for “activation” and enable self-registration, you have to include this in your rule: $_2fDevices =~ /"type":\s*"U2F"/s, else U2F will be required even if users are not registered. This is automatically done when “activation” is set to “on”.

Browser compatibility


If you have enabled self registration, users can register their U2F keys using https://portal/2fregisters


If a user loses its key, you can delete it from the manager Second Factor module. To enable manager Second Factor Administration Module, set enabledModules key in your lemonldap-ng.ini file :

enabledModules = conf, sessions, notifications, 2ndFA

Developer corner

If you have another U2F registration interface, you have to set these keys in Second Factor Devices array (JSON) in your user-database. Then map it to the _2fDevices attribute (see exported variables):

$_2fDevices = [{"name" : "MyU2FKey" , "type" : "U2F" , "_userKey" : "########" , "_keyHandle":"########" , "epoch":"1524078936"}, ...]


_userKey must be base64 encoded

Note that both “origin” and “appId” are fixed to portal URL.