Cost effective One-Time Password solution: How to install yubico’s plugin on Freeradius

If you want One Time Password authentication for your website or your VPN, Yubico propose some cost effective solutions with its yubikeys and its related free open source softwares. In this article we will focus on the Yubikey OTP and its use with Yubico’s RLM plugin for freeradius.

In this case, we will assume you will use the Yubico OTP keys originally provided with your yubico token and hence, the Yubicloud OTP validation service. In a future article, we’ll explain how to configure your own validation server and your own Key Storage Module.

As the point is to be cost effective, no need to spend all your money on this solution. The token will cost you about 30 or 40 Euro depending on the features you need and you can install the Freeradius on a Raspbian for a 40€ Raspberry Pi (or on any Debian server).

As Yubico’s website is not really the most user friendly companion to make this happen, here is a verbatim on how to do it.

I assume you have a Debian Wheezy installed and ready and that you are logged in. As I don’t know if you are using sudo or just su, I will put the command lines as if they were issued for a root user:

1st, we need to install freeradius and a few perl libraries

apt-get install freeradius
apt-get install perl
apt-get install perl-modules
apt-get install libanyevent-perl liburi-perl libanyevent-http-perl libuuid-tiny-perl libdigest-hmac-perl libcrypt-cbc-perl libcrypt-Blowfish-perl

Then we need to download and install the Yubico perl client

cd yubico-perl-client-master/
perl Makefile.PL
make install

after what we can download and install Yubiko’s RLM

cd rlm-yubico-master/
make install

When the software is installed, we need to configure radius to use the plugin. Pay attention, there is a typo in Yubico’s instructions (a _ must be replaced by a -)

First edit the perl module coniguration

vi /etc/freeradius/modules/perl

and add the following line:

module = /usr/share/rlm-yubico/

at the same time you can remove the module= … sample … line.

Then you must edit the default configuration of freeradius

vi /etc/freeradius/sites-available/default

and add “perl” (without quotes) to a line by itself in the “authorize” section. It needs to occur early on, at least before “files” then add “perl” to a line by itself in the “post-auth” section.

Then, finally, you must add the Yubiko’s dictionary

vi /etc/freeradius/dictionary

by adding the following line:

$INCLUDE /usr/share/rlm-yubico/dictionary

Notice the difference between rlm-yubico (here) and rlm_yubico (as mentionned in Yubiko’s instructions)

You just need to restart the freeradius server.

service freeradius restart

OK, the first part is done. We need now to configure it.

Before starting editing configuration files, we need to generate a shared symmetric key for use with the Yubico Web Services. In order to do that, we must go to a Yubiko website  allowing you to generate that key:

There, we will need to authenticate ourself using our Yubikey One-Time Password and provide our e-mail address as a reference. You type your email address and then click on the OTP field and press the button of your Yubikey. You will automatically receivve a screen with a message similar to this one:

Congratulations! Please find below your client identity and client API key.

Client ID: 12345
Secret key: +azAZx123AZaABCDEFGHaAbcdeZ=

Be sure to protect the secret. If you need to generate more client id/keys for your different applications, please come back.

Note that it may take up until 5 minutes until all validation servers know about your newly generated client.

Pretty easy isn’t it?
First we will edit the RLM configuration file:

vi /etc/yubico/rlm/ykrlm-config.cfg

The file will look like that when you will have edited the bold parts:

# Settings for FreeRADIUS authentication of users using YubiKeys.

# Length in characters of the public ID part of Yubikeys
#$id_len = 12;

# List of URLs to use for YubiKey OTP validation
# By default rlm_yubico will target the YubiCloud sync pool:
#$verify_urls = [
# "",
# "",
# "",
# "",
# "",
# It can easily be configured to use a different pool, like a server
# running on localhost:
#$verify_urls = [ "" ];

# Client ID and API key for use with the YubiKey validation service.
# For use with the YubiCloud, you can get an API key here:
#$client_id = 12345;
#$api_key = "+azAZx123AZaABCDEFGHaAbcdeZ=";

# If set to 1, a user with no YubiKey assigned can authenticate using
# any valid YubiKey OTP, which will then cause that key to be assigned
# to the user.
#$allow_auto_provisioning = 1;

# If set to 1, allows a user to omit the username when logging in with
# an already provisioned YubiKey.
#$allow_userless_login = 0;

# Defines who is required to provide a YubiKey OTP when logging in.
# The available levels are:
# 0 = Permissive. OTPs are not required to authenticate, by anyone.
# 1 = Require when provisioned. OTPs are required by all users that
# have a YubiKey assigned to them.
# 2 = Always require. OTPs are required by all users. If no YubiKey
# has been assigned, that user cannot log in, unless auto-provisioning
# is enabled.
$security_level = 2;

# Sets the location of a file containing username to YubiKey mappings.
# Each line of this file should start with a username, followed by : and
# then a comma separated list of public IDs. Lines starting with # or blank
# lines are ignored.
$mapping_file = "/etc/yubico/rlm/ykmapping";

Notice: you can already see how we can configure the RLM to use a local validation server instead of the Yubicloud servers.

Now, we just have to edit the list of users and map the user with one or more yubikey. This is done by editing /etc/yubico/rlm/ykmapping (as we defined it in the config file).

vi /etc/yubico/rlm/ykmapping

We provide the userid and the public identity of the Yubikey(s) of the user. If a user, like JaneDoe hereafter can use more than one Yubikey, we must separate the public identity of the Yubikey by a , (comma). Pay attention NOT to leave a blank between the : and the public ID in the file.

If you don’t know where to find the public identity of your yubikey, you can find it using:

  • the Yubikey personnalization tool: the Yubikey OTP tab should display a Public Identity field with the value in modhex – you just need to remove the whitespace between the letters)
  • Yubico’s OTP demo website ( When trying the Single-Factor authentication, you will get to a “Congratulation” page with a “Technical details” button. If you click on it you will find your identity under the Parameters section, at the line starting with identity=.

Once edited, the file should look like that:

# Maps usernames to YubiKeys.
# Each line should contain a username followed by a :, then followed by a
# comma separated list of YubiKey public IDs.
# For example:

Then you might have to edit the Freeradius server’s configuration to allow you client to connect to it and define a shared secret. This is done by editing the client.conf file in /etc/freeradius directory. Just add your client configuration into the file (there is plenty of examples in the file itself). As an example it could be:

client {
 secret = RadiusPassword
 shortname = private-network

In order to allow us to test the server, we allow the entire subnet to send requests to the Radius server.

By default the Freeradius server will listen to the UDP port 1812. If you want to change that, you might need to edit the radiusd.conf file.

Then you need to configure your user in the freeradius users file and add, for example, a cleartext password for the user:

johndoe            Cleartext-Password := "HisPassword"
janedoe            Cleartext-Password := "HerPassword"

Consequently, johndoe & janedoe will have to type their password before pushing the button on the yubikey to add their OTP in the password field.

Also, depending of the system you will use for authentication, you might need to specify the Radius service type. VPN solution mostly use the Login Service-Type. Consequently, in the users file you will need to specify the type for the users that will use the OTP.

johndoe            Cleartext-Password := "HisPassword"
                   Service-Type = Login-User

Notice: the start of the next line for the user’s definition must be a tabulation.

For johndoe, a password will then start with HisPasswordvvefgfhjjrgf********************** where HisPassword is the password typed by johndoe, vvefgfhjjrgf the Public ID sent has the first part of the OTP when you press the Yubikey’s button then the ************** is the crypted unique 32 characters string generated at that moment by the Yubikey. For more details on what is a Yubikey’s OTP composed of, you can refer to OTP’s explained on Yubico developer’s site.

When it’s done, you need to restart the freeradius server:

service freeradius restart

You can check the server response by configuring your authentication system or using a Radius testing tool (like NTRadPing from Mastersoft – it’s free).

That’s it.

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