---
title: Advanced setup
---


This document describes how Clef can be used in a more secure manner than executing it from your everyday laptop, 
in order to ensure that the keys remain safe in the event that your computer should get compromised. 

## Qubes OS


### Background 

The Qubes operating system is based around virtual machines (qubes), where a set of virtual machines are configured, typically for 
different purposes such as:

- personal
   - Your personal email, browsing etc
- work
  - Work email etc
- vault
  - a VM without network access, where gpg-keys and/or keepass credentials are stored. 

A couple of dedicated virtual machines handle externalities:

- sys-net provides networking to all other (network-enabled) machines
- sys-firewall handles firewall rules
- sys-usb handles USB devices, and can map usb-devices to certain qubes.

The goal of this document is to describe how we can set up clef to provide secure transaction
signing from a `vault` vm, to another networked qube which runs Dapps.

### Setup

There are two ways that this can be achieved: integrated via Qubes or integrated via networking. 


#### 1. Qubes Integrated

Qubes provdes a facility for inter-qubes communication via `qrexec`. A qube can request to make a cross-qube RPC request 
to another qube. The OS then asks the user if the call is permitted. 

![Example](qubes/qrexec-example.png)

A policy-file can be created to allow such interaction. On the `target` domain, a service is invoked which can read the
`stdin` from the `client` qube. 

This is how [Split GPG](https://www.qubes-os.org/doc/split-gpg/) is implemented. We can set up Clef the same way:

##### Server

![Clef via qrexec](qubes/clef_qubes_qrexec.png)

On the `target` qubes, we need to define the rpc service.

[qubes.Clefsign](qubes/qubes.Clefsign):

```bash
#!/bin/bash

SIGNER_BIN="/home/user/tools/clef/clef"
SIGNER_CMD="/home/user/tools/gtksigner/gtkui.py -s $SIGNER_BIN"

# Start clef if not already started
if [ ! -S /home/user/.clef/clef.ipc ]; then
	$SIGNER_CMD &
	sleep 1
fi

# Should be started by now
if [ -S /home/user/.clef/clef.ipc ]; then
    # Post incoming request to HTTP channel
	curl -H "Content-Type: application/json" -X POST -d @- http://localhost:8550 2>/dev/null
fi

```
This RPC service is not complete (see notes about HTTP headers below), but works as a proof-of-concept. 
It will forward the data received on `stdin` (forwarded by the OS) to Clef's HTTP channel.  

It would have been possible to send data directly to the `/home/user/.clef/.clef.ipc` 
socket via e.g `nc -U /home/user/.clef/clef.ipc`, but the reason for sending the request 
data over `HTTP` instead of `IPC` is that we want the ability to forward `HTTP` headers.

To enable the service:

``` bash
sudo cp qubes.Clefsign /etc/qubes-rpc/
sudo chmod +x /etc/qubes-rpc/ qubes.Clefsign
```

This setup uses [gtksigner](https://github.com/holiman/gtksigner), which is a very minimal GTK-based UI that works well 
with minimal requirements. 

##### Client


On the `client` qube, we need to create a listener which will receive the request from the Dapp, and proxy it. 


[qubes-client.py](qubes/client/qubes-client.py):

```python

"""
This implements a dispatcher which listens to localhost:8550, and proxies
requests via qrexec to the service qubes.EthSign on a target domain
"""

import http.server
import socketserver,subprocess

PORT=8550
TARGET_DOMAIN= 'debian-work'

class Dispatcher(http.server.BaseHTTPRequestHandler):
    def do_POST(self):
        post_data = self.rfile.read(int(self.headers['Content-Length']))
        p = subprocess.Popen(['/usr/bin/qrexec-client-vm',TARGET_DOMAIN,'qubes.Clefsign'],stdin=subprocess.PIPE, stdout=subprocess.PIPE)
        output = p.communicate(post_data)[0]
        self.wfile.write(output)


with socketserver.TCPServer(("",PORT), Dispatcher) as httpd:
    print("Serving at port", PORT)
    httpd.serve_forever()


```

#### Testing

To test the flow, if we have set up `debian-work` as the `target`, we can do
 
```bash
$ cat newaccnt.json 
{ "id": 0, "jsonrpc": "2.0","method": "account_new","params": []}

$ cat newaccnt.json| qrexec-client-vm debian-work qubes.Clefsign
```

This should pop up first a dialog to allow the IPC call:

![one](qubes/qubes_newaccount-1.png)

Followed by a GTK-dialog to approve the operation

![two](qubes/qubes_newaccount-2.png)

To test the full flow, we use the client wrapper. Start it on the `client` qube:
```
[user@work qubes]$ python3 qubes-client.py 
```

Make the request over http (`client` qube):
```
[user@work clef]$ cat newaccnt.json | curl -X POST -d @- http://localhost:8550
```
And it should show the same popups again. 

##### Pros and cons

The benefits of this setup are:

- This is the qubes-os intended model for inter-qube communication,
- and thus benefits from qubes-os dialogs and policies for user approval

However, it comes with a couple of drawbacks:

- The `qubes-gpg-client` must forward the http request via RPC to the `target` qube. When doing so, the proxy
  will either drop important headers, or replace them. 
  - The `Host` header is most likely `localhost` 
  - The `Origin` header must be forwarded
  - Information about the remote ip must be added as a `X-Forwarded-For`. However, Clef cannot always trust an `XFF` header, 
  since malicious clients may lie about `XFF` in order to fool the http server into believing it comes from another address.
- Even with a policy in place to allow rpc-calls between `caller` and `target`, there will be several popups:
  - One qubes-specific where the user specifies the `target` vm
  - One clef-specific to approve the transaction
  

#### 2. Network integrated

The second way to set up Clef on a qubes system is to allow networking, and have Clef listen to a port which is accessible
form other qubes. 

![Clef via http](qubes/clef_qubes_http.png)




## USBArmory

The [USB armory](https://inversepath.com/usbarmory) is an open source hardware design with an 800 Mhz ARM processor. It is a pocket-size
computer. When inserted into a laptop, it identifies itself as a USB network interface, basically adding another network
to your computer. Over this new network interface, you can SSH into the device. 

Running Clef off a USB armory means that you can use the armory as a very versatile offline computer, which only
ever connects to a local network between your computer and the device itself.

Needless to say, the while this model should be fairly secure against remote attacks, an attacker with physical access
to the USB Armory would trivially be able to extract the contents of the device filesystem. 

