mirror of
https://github.com/QubesOS/qubes-doc.git
synced 2024-12-11 00:34:31 -05:00
139 lines
5.4 KiB
Markdown
139 lines
5.4 KiB
Markdown
---
|
|
layout: doc
|
|
title: YubiKey in Qubes
|
|
permalink: /doc/yubi-key/
|
|
redirect_from:
|
|
- /en/doc/yubi-key/
|
|
- /doc/YubiKey/
|
|
---
|
|
|
|
Using YubiKey to Qubes authentication
|
|
=====================================
|
|
|
|
You can use YubiKey to enhance Qubes user authentication, for example to mitigate
|
|
risk of snooping the password. This can also slightly improve security when you have [USB keyboard](https://github.com/marmarek/qubes-app-linux-input-proxy).
|
|
|
|
There (at least) two possible configurations: using OTP mode and using challenge-reponse mode.
|
|
|
|
OTP mode
|
|
--------
|
|
|
|
This can be configured using
|
|
[app-linux-yubikey](https://github.com/adubois/qubes-app-linux-yubikey)
|
|
package. This package does not support sharing the same key slot with other
|
|
applications (it will deny further authentications if you try).
|
|
|
|
Contrary to instruction there, currently there is no binary packages in Qubes
|
|
repository and you need to compile it yourself. This can change in the future.
|
|
|
|
Challenge-reponse mode
|
|
----------------------
|
|
|
|
In this mode, your YubiKey will generate response based on secret key, and
|
|
random challenge (instead of counter). This means that it isn't possible to
|
|
generate response in advance even when someone get access to your YubiKey. This
|
|
makes reasonably safe to use the same YubiKey for other services (also in
|
|
challenge-response mode).
|
|
|
|
Same as in OTP case, you will need to setup your YubiKey, choose separate
|
|
password (other than your login password!) and apply the configuration.
|
|
|
|
To use this mode you need:
|
|
|
|
1. Configure your YubiKey for challenge-reponse HMAC-SHA1 mode, for example
|
|
[following this
|
|
tutorial](https://www.yubico.com/products/services-software/personalization-tools/challenge-response/)
|
|
2. Install `ykpers` package in template on which your USB VM is based.
|
|
3. Create `/usr/local/bin/yubikey-auth` script:
|
|
|
|
#!/bin/sh
|
|
|
|
key="$1"
|
|
|
|
if [ -z "$key" ]; then
|
|
echo "Usage: $0 <AESKEY> [<PASSWORD-HASH>]"
|
|
exit 1
|
|
fi
|
|
|
|
# if password has given, verify it
|
|
if [ -n "$2" ]; then
|
|
# PAM appends \0 at the end
|
|
hash=`head -c -1 | openssl dgst -sha1 -r | cut -f1 -d ' '`
|
|
if [ "x$2" != "x$hash" ]; then
|
|
exit 1
|
|
fi
|
|
fi
|
|
|
|
challenge=`head -c64 /dev/urandom | xxd -c 64 -ps`
|
|
# You may need to adjust slot number and USB VM name here
|
|
response=`qvm-run -u root --nogui -p sys-usb "ykchalresp -2 -x $challenge"`
|
|
|
|
correct_response=`echo $challenge | xxd -r -ps | openssl dgst -sha1 -macopt hexkey:$key -mac HMAC -r | cut -f1 -d ' '`
|
|
|
|
test "x$correct_response" = "x$response"
|
|
exit $?
|
|
|
|
4. Adjust USB VM name (`sys-usb` above), and possibly YubiKey slot number (`2`
|
|
above), then make the script executable.
|
|
5. Edit `/etc/pam.d/xscreensaver` (or appropriate file if you are using other
|
|
screen locker program). Add this line at the beginning:
|
|
|
|
auth [success=done default=ignore] pam_exec.so expose_authtok quiet /usr/local/bin/yubikey-auth AESKEY PASSWORD-HASH
|
|
|
|
Replace `AESKEY` with hex-encoded key configured in the first step, then
|
|
replace `PASSWORD-HASH` with SHA1 hash for your YubiKey-linked password (other
|
|
than your standard Qubes password). You can calculate it using this command:
|
|
|
|
echo -n "PASSWORD" | openssl dgst -sha1
|
|
|
|
### Usage
|
|
|
|
When you want to unlock your screen, plug YubiKey into USB slot, then enter
|
|
password associated with YubiKey. If you configured so, YubiKey will request
|
|
confirmation by pressing button on it (it will blink).
|
|
When everything is ok, your screen will be unlocked.
|
|
|
|
In any case you can still use your login password, but do it in secure location
|
|
where no one can snoop your password.
|
|
|
|
Locking the screen when YubiKey is removed
|
|
------------------------------------------
|
|
|
|
You can setup your system to automatically lock the screen when you unplug
|
|
YubiKey. This will require creating simple qrexec service which will expose
|
|
ability to lock the screen to your USB VM, and then adding udev hook to
|
|
actually call that service.
|
|
|
|
1. First configure the qrexec service. Create `/etc/qubes-rpc/custom.LockScreen` (in dom0)
|
|
with simple command to lock the screen. In case of xscreensaver (used in Xfce)
|
|
it would be:
|
|
|
|
DISPLAY=:0 xscreensaver-command -lock
|
|
|
|
2. Allow your USB VM to call that service. Assuming that its named `sys-usb` it
|
|
would require creating `/etc/qubes-rpc/policy/custom.LockScreen` with:
|
|
|
|
sys-usb dom0 allow
|
|
|
|
3. Create udev hook in your USB VM. Store it in `/rw/config` to have it
|
|
persistent across VM restarts. For example name the file
|
|
`/rw/config/yubikey.rules`. Write there single line:
|
|
|
|
ACTION=="remove", SUBSYSTEM=="usb", ENV{ID_SECURITY_TOKEN}=="1", RUN+="/usr/bin/qrexec-client-vm dom0 custom.LockScreen"
|
|
|
|
4. Ensure that the udev hook is placed in the right place after VM restart. Append to `/rw/config/rc.local`:
|
|
|
|
ln -s /rw/config/yubikey.rules /etc/udev/rules.d/
|
|
udevadm control --reload
|
|
|
|
Then make `/rw/config/rc.local` executable. For changes to take effect, you
|
|
need to call this script manually for the first time.
|
|
|
|
If you use KDE, the command(s) in first step would be different:
|
|
|
|
# In case of USB VM being autostarted, it will not have direct access to D-Bus
|
|
# session bus, so find its address manually:
|
|
kde_pid=`pidof kdeinit4`
|
|
export `cat /proc/$kde_pid/environ|grep -ao 'DBUS_SESSION_BUS_ADDRESS=[[:graph:]]*'`
|
|
qdbus org.freedesktop.ScreenSaver /ScreenSaver Lock
|