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191 lines
7.7 KiB
Markdown
---
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layout: doc
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title: Multifactor Authentication
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permalink: /doc/multifactor-authentication/
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redirect_from:
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- /en/doc/multifactor-authentication/
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- /doc/Multi-factorAuthentication/
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---
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Using Multi-factor Authentication with Qubes
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============================================
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(Note: This page concerns multi-factor authentication for logging into external
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services, not for logging into Qubes itself. For the latter, see
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[here][YubiKey].)
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[Multi-factor authentication (MFA)][MFA] today most commonly takes the form of a
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numerical code generated by a smartphone app or sent via SMS (text message)
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which the user must enter in addition to a password in order to log in to a
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website or other service.
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One of the primary features of Qubes is that it allows us to create securely
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isolated VMs which can run arbitrary programs. (These VMs are securely isolated
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not only from each other but also, optionally, from the network.) This means
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that we can create a dedicated, network-isolated VM to function as a secure
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authenticator.
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This guide will show you how to set up a VM which uses [oathtool][], an
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open-source one-time password tool, to generate authentication codes. This
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method presents several benefits over relying on a consumer smartphone app or
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SMS:
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* `oathtool` includes the [time-based one-time password (TOTP)][TOTP]
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algorithm, which is the same algorithm used by [Google Authenticator][], one
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of the most commonly used authenticator apps. This means that we can use
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`oathtool` as a complete open-source replacement for Google Authenticator
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(which became propriety (closed-source) in May 2013 after version 2.21).
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* By keeping all of our authenticator data as plain text files in a dedicated
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VM, we have complete control over the secret keys used to generate our
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authentication tokens, and we can back up, copy, and transfer our
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authenticator data at will.
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* By creating a minimal environment in which to run `oathtool` from the command
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line, we can minimize our attack surface relative to most smartphone apps and
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SMS. Consumer smartphones are typically internet-facing devices which are
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increasingly targeted by malware. Most smartphones are bundled with
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proprietary software which allows service providers almost complete control
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over the device. Likewise, consumer SMS messages are often cleartext
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communications which can feasibly be intercepted and read by third parties.
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(In cases in which SMS messages are encrypted on the network by the service
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provider, the service provider itself still has full access, which means that
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the contents of such messages could be read by unscrupulous admins or turned
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over to government agencies.)
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* Using `oathtool` in a dedicated, network-isolated Qubes VM allows us to
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achieve a unique combination of security and convenience. The strong isolation
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Qubes provides allows us to reap the full security benefits of MFA, while
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virtualization frees us from having to worry about finding and handling a
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second physical device.
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Optional Preparation Steps
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--------------------------
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1. Start with a minimal template. In this example, we'll use the
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[minimal Fedora template][FedoraMinimal]. Get it if you haven't already done
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so:
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[user@dom0 ~]$ sudo qubes-dom0-update qubes-template-fedora-30-minimal
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2. Since we'll be making some modifications, you may want to clone the minimal
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template:
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[user@dom0 ~]$ qvm-clone fedora-30-minimal fedora-30-min-mfa
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3. To open a root shell on the minimal template (for details, see [Passwordless Root]), run the following command:
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[user@dom0 ~]$ qvm-run -u root fedora-30-min-mfa xterm
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4. Since this is going to be a minimal environment in which we run `oathtool`
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from the command line, we'll install only a couple of packages:
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[root@fedora-30-min-mfa ~]# dnf install oathtool vim-minimal
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[root@fedora-30-min-mfa ~]$ poweroff
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5. Create an AppVM and set it to use the TemplateVM we just created:
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[user@dom0 ~]$ qvm-create -l black mfa
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[user@dom0 ~]$ qvm-prefs -s mfa template fedora-30-min-mfa
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6. Isolate the new AppVM from the network:
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[user@dom0 ~]$ qvm-prefs -s mfa netvm none
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Using the MFA AppVM
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-------------------
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Now that we have an AppVM set up to use `oathtool` securely, let's use it with
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an external service. This process will vary slightly from service to service but
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is largely the same.
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1. Proceed with setting up multi-factor authentication as you normally would.
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If you are prompted to scan a QR code, instead select the option (if
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available) to view the secret key as text:
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You should then see the secret key as text:
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Note that the length and format of the secret key may vary by service:
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2. In your MFA AppVM, you can now use `oathtool` to generate base32 TOTP
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authentication tokens just like Google Authenticator would. In this example,
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we'll use the secret key `xd2n mx5t ekg6 h6bi u74d 745k n4m7 zy3x` from the
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second image above (substitute your own):
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[user@mfa ~]$ oathtool --base32 --totp "xd2n mx5t ekg6 h6bi u74d 745k n4m7 zy3x"
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279365
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The output is `279365`. This is what you would enter when prompted for an
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authenticator code. (Note that this is a *time*-based one-time password,
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which means that your VM's clock must be sufficiently accurate in order to
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generate a valid token. Qubes handles VM time syncing automatically, so you
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normally shouldn't have to worry about this. As usual, the token will change
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after a short period of time.)
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3. To make this easier on ourselves in the future, we can create a simple shell
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script for each service we use. (The example service here is a Google
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account, using the example key from above. You'll get a unique secret key
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from each service.) Create the script like so:
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[user@mfa ~]$ > google
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[user@mfa ~]$ vi google
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#!/usr/bin/env bash
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##My Google Account
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##me@gmail.com
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oathtool --base32 --totp "xd2n mx5t ekg6 h6bi u74d 745k n4m7 zy3x"
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[user@mfa ~]$ chmod +x google
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Since the secret key stored in the script never changes, we should never
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have to update this script, but we can easily do so if we ever want to.
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4. Now, whenever Google prompts us for an authenticator code, all we have to do
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is this:
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[user@mfa ~]$ ./google
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640916
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Done!
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5. Now you can create scripts for any other TOTP-supporting services you use,
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and enjoy the security and ease of quickly generating authentication tokens
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right from your Qubes VM command-line:
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[user@mfa ~]$ ./github
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495272
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[user@mfa ~]$ ./aws
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396732
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[user@mfa ~]$ ./facebook
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851956
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[user@mfa ~]$ ./dropbox
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294106
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[user@mfa ~]$ ./microsoft
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295592
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[user@mfa ~]$ ./slack
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501731
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[user@mfa ~]$ ./wordpress
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914625
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[user@mfa ~]$ ./tumblr
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701463
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For a more complete list of compatible services, see [here][usage].
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[YubiKey]: /doc/YubiKey/
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[MFA]: https://en.wikipedia.org/wiki/Multi-factor_authentication
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[oathtool]: http://www.nongnu.org/oath-toolkit/man-oathtool.html
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[TOTP]: https://en.wikipedia.org/wiki/Time-based_One-time_Password_Algorithm
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[Google Authenticator]: https://en.wikipedia.org/wiki/Google_Authenticator
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[FedoraMinimal]: /doc/Templates/FedoraMinimal/
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[usage]: https://en.wikipedia.org/wiki/Google_Authenticator#Usage
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[Passwordless Root]: /doc/templates/minimal/#passwordless-root
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