Remote disk unlocking: Difference between revisions
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If you want to unlock your computer remotely via SSH or even through Tor, and you are facing the problem, that you can’t reach your computer before your computer is unlocked. Tor will help you to reach your computer, even during the boot process. | |||
== Setup == | |||
Generate host key for the SSH daemon which will run in initrd during boot | |||
= | <syntaxhighlight lang="bash"> | ||
# ssh-keygen -t ed25519 -N "" -f /etc/secrets/initrd/ssh_host_ed25519_key | |||
</syntaxhighlight> | |||
Enable SSH daemon in initrd | |||
{{file|/etc/nixos/configuration.nix|nix|<nowiki> | |||
boot.initrd = { | |||
availableKernelModules = [ "r8169" ]; | |||
network = { | |||
enable = true; | |||
udhcpc.enable = true; | |||
flushBeforeStage2 = true; | |||
ssh = { | |||
enable = true; | |||
port = 22; | |||
authorizedKeys = [ "ssh-rsa AAAAyourpublic-key-here..." ]; | |||
hostKeys = [ "/etc/secrets/initrd/ssh_host_ed25519_key" ]; | |||
}; | |||
postCommands = '' | |||
# Automatically ask for the password on SSH login | |||
echo 'cryptsetup-askpass || echo "Unlock was successful; exiting SSH session" && exit 1'</nowiki> >> <nowiki>/root/.profile | |||
''; | |||
}; | |||
}; | |||
</nowiki>}} | |||
Adapt following parts according to your setup | |||
* '''authorizedKeys''': Add the SSH public keys for the users which should be able to authenticate to the SSH daemon to the <code>authorizedKeys</code> option. | |||
* '''availableKernelModules''': Most likely your network card is not working without its kernel module being part of the initrd, so you have to find out which module is used for your network. Use <code>lspci -v | grep -iA8 'network\|ethernet'</code> for that. | |||
* '''kernelParams''': Instead of using DHCP you could also configure a static IP, for example with kernel parameter <code>boot.kernelParams = [ "ip=10.25.0.2::10.25.0.1:255.255.255.0:myhost::none" ];</code>, where <code>10.25.0.2</code> is the client IP, <code>10.25.0.1</code> is the gateway IP. See [https://www.kernel.org/doc/Documentation/filesystems/nfs/nfsroot.txt the kernel documentation] for more information on the <code>ip=</code> parameter. When using DHCP, make sure your computer is always attached to the network and is able to get an IP adress, or the boot process will hang. | |||
The <code>postCommands</code> option is necessary to get a password prompt instead of a shell. | |||
If you omit it, you will get dropped into <code>/bin/ash</code>, and you will have to manually run <code>cryptsetup-askpass</code> to enter the password. Alternatively, the <code>boot.initrd.systemd.users.root.shell</code> option can be set to <code>/bin/conspy</code> for passwords which expect stdin. This binary included by default, and provided by busybox. | |||
== Usage == | |||
After reboot, connect to the initrd SSH daemon using | |||
< | <syntaxhighlight lang="bash"> | ||
# ssh root@10.25.0.2 | |||
</syntaxhighlight> | |||
Where <code>10.25.0.2</code> is the IP which is acquired via DHCP or configured via the kernel parameter. | |||
== Tips and tricks == | |||
=== | === Bcachefs unlocking === | ||
Unlocking encrypted Bcachefs root filesystems is [https://github.com/NixOS/nixpkgs/issues/291529 not yet supported]. As a workaround, following script, in combination with the setup above, can be used as SSH shell, to unlock the disk <code>/dev/vda2</code>. | |||
< | {{file|/etc/nixos/configuration.nix|nix|<nowiki> | ||
boot.initrd. | boot.initrd.systemd = let | ||
askPass = pkgs.writeShellScriptBin "bcachefs-askpass" '' | |||
keyctl link @u @s | |||
mkdir /sysroot | |||
until bcachefs mount /dev/vda2 /sysroot | |||
do | |||
sleep 1 | |||
done | |||
''; | |||
in { | |||
enable = true; | enable = true; | ||
initrdBin = with pkgs; [ keyutils ]; | |||
storePaths = ["${askPass}/bin/bcachefs-askpass"]; | |||
users.root.shell = "${askPass}/bin/bcachefs-askpass"; | |||
}; | }; | ||
</ | </nowiki>}} | ||
Using systemd in initrd automatically continues the boot process after the target <code>/sysroot</code> is mounted. | |||
=== Tor in initrd === | |||
= | An example with an ssh server listening at a tor hidden service address can be found at [https://cgit.euer.krebsco.de/stockholm/tree/krebs/2configs/tor/initrd.nix?id=9919cb25912dfcc50881239f95494dd2f8e7b858 krebs/2configs/tor/initrd.nix in stockholm] | ||
=== Prepare the Onion ID === | ==== Prepare the Onion ID ==== | ||
You need 3 files to create an onion id (a.k.a. tor hidden service). | You need 3 files to create an onion id (a.k.a. tor hidden service). | ||
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* <code>hs_ed25519_secret_key</code> | * <code>hs_ed25519_secret_key</code> | ||
To create | To create these files, you have to run tor once, with a dummy configuration. | ||
<pre>DataDirectory /tmp/my-dummy.tor/ | <pre>DataDirectory /tmp/my-dummy.tor/ | ||
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Hit <code>Ctrl-C</code> and the files you need, should be in <code>/home/tony/tor/onion</code>. | Hit <code>Ctrl-C</code> and the files you need, should be in <code>/home/tony/tor/onion</code>. | ||
=== Setup Tor === | ==== Setup Tor ==== | ||
Now that you have your 3 files, you have to script a bit, but it’s not too complicated. | Now that you have your 3 files, you have to script a bit, but it’s not too complicated. | ||
< | <syntaxhighlight lang="nix"># copy your onion folder | ||
boot.initrd.secrets = { | boot.initrd.secrets = { | ||
"/etc/tor/onion/bootup"; = /home/tony/tor/onion; # maybe find a better spot to store this. | |||
}; | }; | ||
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# start tor during boot process | # start tor during boot process | ||
boot.initrd.network.postCommands = let | boot.initrd.network.postCommands = let | ||
torRc = (pkgs.writeText | torRc = (pkgs.writeText "tor.rc" '' | ||
DataDirectory /etc/tor | DataDirectory /etc/tor | ||
SOCKSPort 127.0.0.1:9050 IsolateDestAddr | SOCKSPort 127.0.0.1:9050 IsolateDestAddr | ||
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''); | ''); | ||
in '' | in '' | ||
echo | echo "tor: preparing onion folder" | ||
# have to do this otherwise tor does not want to start | # have to do this otherwise tor does not want to start | ||
chmod -R 700 /etc/tor | chmod -R 700 /etc/tor | ||
echo | echo "make sure localhost is up" | ||
ip a a 127.0.0.1/8 dev lo | ip a a 127.0.0.1/8 dev lo | ||
ip link set lo up | ip link set lo up | ||
echo | echo "tor: starting tor" | ||
tor -f ${torRc} --verify-config | tor -f ${torRc} --verify-config | ||
tor -f ${torRc} & | tor -f ${torRc} & | ||
'';</ | '';</syntaxhighlight> | ||
That was it. Tor should be running during your boot process. | That was it. Tor should be running during your boot process. | ||
=== Setup haveged === | ==== Setup haveged ==== | ||
If your system doesn't gather enough entropy the startup time of tor is rather long (2:42 vs 0:06 on a RPi 4b). Counter it by starting <code>haveged</code>. | If your system doesn't gather enough entropy the startup time of tor is rather long (2:42 vs 0:06 on a RPi 4b). Counter it by starting <code>haveged</code>. | ||
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</pre> | </pre> | ||
Then use this snippet before <code>echo | Then use this snippet before <code>echo "tor: starting tor"</code> in your <code>boot.initrd.network.postCommands</code>. | ||
<pre> | <pre> | ||
echo "haveged: starting haveged" | echo "haveged: starting haveged" | ||
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</pre> | </pre> | ||
=== Setup ntpdate === | ==== Setup ntpdate ==== | ||
If your system doesn't utilize a RTC you've to ensure time is correctly set before startup of tor. | If your system doesn't utilize a RTC you've to ensure time is correctly set before startup of tor. | ||
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</pre> | </pre> | ||
Then use this snippet before <code>echo | Then use this snippet before <code>echo "tor: starting tor"</code> in your <code>boot.initrd.network.postCommands</code>. | ||
<pre> | <pre> | ||
echo "ntp: starting ntpdate" | echo "ntp: starting ntpdate" | ||
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</pre> | </pre> | ||
== | ==== Usage ==== | ||
When your computer boots, and asks for the LUKS password. Now you can unlock your encrypted Hard drive using: | When your computer boots, and asks for the LUKS password. Now you can unlock your encrypted Hard drive using: | ||
<pre>torify ssh root@ | <pre>torify ssh root@<onion.id>.onion -p 22 'my-secret-password'</pre> | ||
== | === Enable Wifi in initrd === | ||
Following example configuration by [https://discourse.nixos.org/t/wireless-connection-within-initrd/38317/13 @loutr] enables wifi connections inside initrd. Replace interface name <code>wlp0s20f0u4</code> with the name of your wifi adapter. Depending on your wifi device, you might need to add different kernel modules.<syntaxhighlight lang="nix"> | |||
boot.initrd = { | |||
# crypto coprocessor and wifi modules | |||
availableKernelModules = [ "ccm" "ctr" "iwlmvm" "iwlwifi" ]; | |||
systemd = { | |||
enable = true; | |||
packages = [ pkgs.wpa_supplicant ]; | |||
initrdBin = [ pkgs.wpa_supplicant ]; | |||
targets.initrd.wants = [ "wpa_supplicant@wlp0s20f0u4.service" ]; | |||
# prevent WPA supplicant from requiring `sysinit.target`. | |||
services."wpa_supplicant@".unitConfig.DefaultDependencies = false; | |||
users.root.shell = "/bin/systemd-tty-ask-password-agent"; | |||
network = { | |||
enable = true; | |||
networks."10-wlan" = { | |||
matchConfig.Name = "wlp0s20f0u4"; | |||
networkConfig.DHCP = "yes"; | |||
}; | |||
ssh = { | |||
enable = true; | |||
port = 22; | |||
hostKeys = [ "/etc/ssh/ssh_host_ed25519_key" ]; | |||
authorizedKeys = default.user.openssh.authorizedKeys.keys; | |||
}; | |||
}; | |||
secrets."/etc/wpa_supplicant/wpa_supplicant-wlp0s20f0u4.conf" = /root/secrets/wpa_supplicant.conf; | |||
}; | |||
</syntaxhighlight>The file <code>wpa_supplicat-wlp0s20f0u4.conf</code> is the wireless profile used by [[wpa_supplicant]] which will get copied into the initramfs. | |||
[[Category:Server]] | |||
[[Category:Cookbook]] |