(best) Split SSH setup guide

deeplow · December 24, 2020, 3:13pm

We forgot to update here, but there was a collaboration to produce a full Qubes Split-SSH Guide that is now here:

Qubes-Community/Contents/blob/master/docs/configuration/split-ssh.md

# Qubes Split SSH

Split SSH implements a concept similar to having a smart card with your private SSH keys, except that the role of the “smart card” is played by another Qubes AppVM. 
This Qubes setup allows you to keep your SSH private keys in a vault VM (`vault`) while using an SSH Client VM (`ssh-client`) to access your remote server. 
This is done by using Qubes's [qrexec][qrexec] framework to connect a local SSH Agent socket from your SSH Client VM to the SSH Agent socket within the vault VM. 
This way the compromise of the domain you use to connect to your remote server does not allow the attacker to automatically also steal all your keys. 
(We should make a rather obvious comment here that the so-often-used passphrases on private keys are pretty meaningless because the attacker can easily set up a simple backdoor which would wait until the user enters the passphrase and steal the key then.)

   ![diagram](https://raw.githubusercontent.com/santorihelix/qubes-splitssh-diagram/main/split-ssh-keepassxc-8.svg)

## Security Benefits

In the setup described in this guide, even an attacker who manages to gain access to the `ssh-client`  VM will not be able to obtain the user’s private key since it is simply not there. 
Rather, the private key remains in the `vault` VM, which is extremely unlikely to be compromised if nothing is ever copied or transferred into it. 
In order to gain access to the vault VM, the attacker would require the use of, e.g., a general Xen VM escape exploit or a signed, compromised package which is already installed in the TemplateVM upon which the vault VM is based.

## Overview

1. Make sure the TemplateVM you plan to use is up to date.
2. Create `vault` and `ssh-client` AppVMs.

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It’s a result of work by @phl @santorihelix @whoami and I oriented it a bit.