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87 lines
3.2 KiB
Markdown
87 lines
3.2 KiB
Markdown
---
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title: "Using Split GPG and Split SSH on Qubes OS"
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date: 2022-08-13
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tags: ['Operating Systems', 'Qubes OS', 'Security']
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author: Tommy
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---
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This post will go over setting up Split GPG, then setting up Split SSH with the same PGP keys. Effectively, we are emulating what you can do with a PGP smartcard on Qubes OS.
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## Split GPG
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Follow the official Qubes OS [documentation](https://www.qubes-os.org/doc/split-gpg/) to set this up.
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Note that if you already have a PGP key with a passphrase, you can remove it by installing `pinentry-gtk` to `vault`'s TemplateVM, then run `gpg2 --edit-key <key_id>` and `passwd` to set an empty passphrase. The default non-graphical pinentry will just make an infinite loop and will not allow you to set an empty passphrase.
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## Split SSH
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This part is based on the Qubes Community's [guide](https://forum.qubes-os.org/t/split-ssh/19060); however, I will deviate from it to use the PGP keys for SSH instead of generating a new key pair.
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### In `dom0`
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- Create `/etc/qubes-rpc/policy/qubes.SshAgent` with `@anyvm @anyvm ask,default_target=vault` as the content. Since the keys are not passphrase protected, you should **not** set the policy to allow.
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### In `vault` AppVM
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- Add `enable-ssh-support` to the end of `~/.gnupg/gpg-agent.conf`
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- Get your keygrip with `gpg --with-keygrip -k`
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- Add your keygrip to the end of `~/.gnupg/sshcontrol`
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### In `vault`'s TemplateVM
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- Create `/etc/qubes-rpc/qubes.SshAgent` with the following content:
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```bash
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#!/bin/sh
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# Qubes App Split SSH Script
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# Activate GPG Agent and set the correct SSH socket
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export SSH_AUTH_SOCK=$(gpgconf --list-dirs agent-ssh-socket)
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gpgconf --launch gpg-agent
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# safeguard - Qubes notification bubble for each ssh request
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notify-send "[$(qubesdb-read /name)] SSH agent access from: $QREXEC_REMOTE_DOMAIN"
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# SSH connection
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socat - "UNIX-CONNECT:$SSH_AUTH_SOCK"
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```
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- Make it executable with `sudo chmod +x /etc/qubes-rpc/qubes.SshAgent`
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- Turn off the templateVM. If the `vault` VM is running, turn it off, then start it to update the VM's configuration.
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### In `ssh-client` AppVM
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- Add the following to the end of `/rw/config/rc.local`:
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```bash
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# SPLIT SSH CONFIGURATION >>>
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# replace "vault" with your AppVM name which stores the ssh private key(s)
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SSH_VAULT_VM="vault"
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if [ "$SSH_VAULT_VM" != "" ]; then
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export SSH_SOCK="/home/user/.SSH_AGENT_$SSH_VAULT_VM"
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rm -f "$SSH_SOCK"
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sudo -u user /bin/sh -c "umask 177 && exec socat 'UNIX-LISTEN:$SSH_SOCK,fork' 'EXEC:qrexec-client-vm $SSH_VAULT_VM qubes.SshAgent'" &
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fi
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# <<< SPLIT SSH CONFIGURATION
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```
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- Add the following to the end of `~/bash.rc`:
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```bash
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# SPLIT SSH CONFIGURATION >>>
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# replace "vault" with your AppVM name which stores the ssh private key(s)
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SSH_VAULT_VM="vault"
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if [ "$SSH_VAULT_VM" != "" ]; then
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export SSH_AUTH_SOCK="/home/user/.SSH_AGENT_$SSH_VAULT_VM"
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fi
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# <<< SPLIT SSH CONFIGURATION
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```
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- Restart `ssh-client` and confirm if it's working with `ssh-add -L`.
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### Limitations
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A malicious `ssh-client` AppVM can hold onto the ssh-agent connection for more than one use until it is shut down. While your private key is protected, a malicious actor with access to the AppVM can still abuse the ssh-agent to log into your servers.
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