
Using Multi-factor Authentication with Qubes
============================================

(Note: This page concerns multi-factor authentication for logging into external
services, not for logging into Qubes itself. For the latter, see
[here][YubiKey].)

[Multi-factor authentication (MFA)][MFA] today most commonly takes the form of a
numerical code generated by a smartphone app or sent via SMS (text message)
which the user must enter in addition to a password in order to log in to a
website or other service.

One of the primary features of Qubes is that it allows us to create securely
isolated VMs which can run arbitrary programs. (These VMs are securely isolated
not only from each other but also, optionally, from the network.) This means
that we can create a dedicated, network-isolated VM to function as a secure
authenticator.

This guide will show you how to set up a VM which uses [oathtool][], an
open-source one-time password tool, to generate authentication codes. This
method presents several benefits over relying on a consumer smartphone app or
SMS:

 * `oathtool` includes the [time-based one-time password (TOTP)][TOTP]
   algorithm, which is the same algorithm used by [Google Authenticator][], one
   of the most commonly used authenticator apps. This means that we can use
   `oathtool` as a complete open-source replacement for Google Authenticator
   (which became propriety (closed-source) in May 2013 after version 2.21).

 * By keeping all of our authenticator data as plain text files in a dedicated
   VM, we have complete control over the secret keys used to generate our
   authentication tokens, and we can back up, copy, and transfer our
   authenticator data at will.

 * By creating a minimal environment in which to run `oathtool` from the command
   line, we can minimize our attack surface relative to most smartphone apps and
   SMS. Consumer smartphones are typically internet-facing devices which are
   increasingly targeted by malware. Most smartphones are bundled with
   proprietary software which allows service providers almost complete control
   over the device. Likewise, consumer SMS messages are often cleartext
   communications which can feasibly be intercepted and read by third parties.
   (In cases in which SMS messages are encrypted on the network by the service
   provider, the service provider itself still has full access, which means that
   the contents of such messages could be read by unscrupulous admins or turned
   over to government agencies.)

 * Using `oathtool` in a dedicated, network-isolated Qubes VM allows us to
   achieve a unique combination of security and convenience. The strong isolation
   Qubes provides allows us to reap the full security benefits of MFA, while
   virtualization frees us from having to worry about finding and handling a
   second physical device.


Optional Preparation Steps
--------------------------

 1. Start with a minimal template. In this example, we'll use the
    [minimal Fedora template][FedoraMinimal]. Get it if you haven't already done
    so:

        [user@dom0 ~]$ sudo qubes-dom0-update qubes-template-fedora-30-minimal

 2. Since we'll be making some modifications, you may want to clone the minimal
    template:

        [user@dom0 ~]$ qvm-clone fedora-30-minimal fedora-30-min-mfa
 
 3. To open a root shell on the minimal template (for details, see [Passwordless Root]), run the following command:

        [user@dom0 ~]$ qvm-run -u root fedora-30-min-mfa xterm

 4. Since this is going to be a minimal environment in which we run `oathtool`
    from the command line, we'll install only a couple of packages:

        [root@fedora-30-min-mfa ~]# dnf install oathtool vim-minimal
        [root@fedora-30-min-mfa ~]$ poweroff

 5. Create an AppVM and set it to use the TemplateVM we just created:

        [user@dom0 ~]$ qvm-create -l black mfa
        [user@dom0 ~]$ qvm-prefs -s mfa template fedora-30-min-mfa

 6. Isolate the new AppVM from the network:

        [user@dom0 ~]$ qvm-prefs -s mfa netvm none


Using the MFA AppVM
-------------------

Now that we have an AppVM set up to use `oathtool` securely, let's use it with
an external service. This process will vary slightly from service to service but
is largely the same.

 1. Proceed with setting up multi-factor authentication as you normally would.
    If you are prompted to scan a QR code, instead select the option (if
    available) to view the secret key as text:

    ![Secret Key Example 0](/attachment/wiki/Multi-factorAuthentication/secret-key-example-0.png)

    You should then see the secret key as text:

    ![Secret Key Example 1](/attachment/wiki/Multi-factorAuthentication/secret-key-example-1.png)

    Note that the length and format of the secret key may vary by service:

    ![Secret Key Example 2](/attachment/wiki/Multi-factorAuthentication/secret-key-example-2.png)

 2. In your MFA AppVM, you can now use `oathtool` to generate base32 TOTP
    authentication tokens just like Google Authenticator would. In this example,
    we'll use the secret key `xd2n mx5t ekg6 h6bi u74d 745k n4m7 zy3x` from the
    second image above (substitute your own):

        [user@mfa ~]$ oathtool --base32 --totp "xd2n mx5t ekg6 h6bi u74d 745k n4m7 zy3x"
        279365

    The output is `279365`. This is what you would enter when prompted for an
    authenticator code. (Note that this is a *time*-based one-time password,
    which means that your VM's clock must be sufficiently accurate in order to
    generate a valid token. Qubes handles VM time syncing automatically, so you
    normally shouldn't have to worry about this. As usual, the token will change
    after a short period of time.)

 3. To make this easier on ourselves in the future, we can create a simple shell
    script for each service we use. (The example service here is a Google
    account, using the example key from above. You'll get a unique secret key
    from each service.) Create the script like so:

        [user@mfa ~]$ > google
        [user@mfa ~]$ vi google

        #!/usr/bin/env bash
        ##My Google Account
        ##me@gmail.com
        oathtool --base32 --totp "xd2n mx5t ekg6 h6bi u74d 745k n4m7 zy3x"

        [user@mfa ~]$ chmod +x google

    Since the secret key stored in the script never changes, we should never
    have to update this script, but we can easily do so if we ever want to.

 4. Now, whenever Google prompts us for an authenticator code, all we have to do
    is this:

        [user@mfa ~]$ ./google
        640916

    Done!

 5. Now you can create scripts for any other TOTP-supporting services you use,
    and enjoy the security and ease of quickly generating authentication tokens
    right from your Qubes VM command-line:

        [user@mfa ~]$ ./github
        495272
        [user@mfa ~]$ ./aws
        396732
        [user@mfa ~]$ ./facebook
        851956
        [user@mfa ~]$ ./dropbox
        294106
        [user@mfa ~]$ ./microsoft
        295592
        [user@mfa ~]$ ./slack
        501731
        [user@mfa ~]$ ./wordpress
        914625
        [user@mfa ~]$ ./tumblr
        701463

    For a more complete list of compatible services, see [here][usage].


[YubiKey]: https://www.qubes-os.org/doc/YubiKey/
[MFA]: https://en.wikipedia.org/wiki/Multi-factor_authentication
[oathtool]: http://www.nongnu.org/oath-toolkit/man-oathtool.html
[TOTP]: https://en.wikipedia.org/wiki/Time-based_One-time_Password_Algorithm
[Google Authenticator]: https://en.wikipedia.org/wiki/Google_Authenticator
[FedoraMinimal]: https://www.qubes-os.org/doc/Templates/FedoraMinimal/
[usage]: https://en.wikipedia.org/wiki/Google_Authenticator#Usage
[Passwordless Root]: https://www.qubes-os.org/doc/templates/minimal/#passwordless-root
