Raspberry Pi VPN Hotspot (or How To Infuriate Theresa May For Under £40)

As you’re no-doubt aware, Home Secretary Theresa May is probably going to get her way with her “snooper’s charter” by capitalising on events in Paris (even though that makes no sense), and before long, people working for law enforcement will be able to read your Internet usage history without so much as a warrant (or, to put it as the UN’s privacy chief put it, it’s “worse than scary”).

John Oliver on Last Week Tonight discusses the bill.
Or as John Oliver put it, “This bill could write into law a huge invasion of privacy.” Click to see a clip.

In a revelation that we should be thankful of as much as we’re terrified by, our government does not understand how the Internet works. And that’s why it’s really easy for somebody with only a modicum of geekery to almost-completely hide their online activities from observation by their government and simultaneously from hackers. Here’s a device that I built the other weekend, and below I’ll tell you how to do it yourself (and how it keeps you safe online from a variety of threats, as well as potentially giving you certain other advantages online):

"Iceland", one of my Raspberry Pi VPN hotspots
It’s small, it’s cute, and it goes a long way to protecting my privacy online.

I call it “Iceland”, for reasons that will become clear later. But a more-descriptive name would be a “Raspberry Pi VPN Hotspot”. Here’s what you’ll need if you want to build one:

  • A Raspberry Pi Model B (or later) – you can get these from less than £30 online and it’ll come with an SD card that’ll let it boot Raspbian, which is the Linux distribution I’ve used in my example: there’s no reason you couldn’t use another one if you’re familiar with it
  • A USB WiFi dongle that supports “access point” mode – I’m using an Edimax one that cost me under a fiver – but it took a little hacking to make it work – I’ve heard that Panda and RALink dongles are easier
  • A subscription to a VPN with OpenVPN support and at least one endpoint outside of the UK – I’m using VyprVPN because I have a special offer, but there are lots of cheaper options: here’s a great article about choosing one
  • A basic familiarity with a *nix command line, an elementary understanding of IP networking, and a spare 20 minutes.

From here on, this post gets pretty geeky. Unless you plan on building your own little box to encrypt all of your home’s WiFi traffic until it’s well out of the UK and close-to-impossible to link to you personally (which you should!), then you probably ought to come back to it another time.

Here’s how it’s done:

1. Plug in, boot, and install some prerequisites

Plug the WiFi dongle into a USB port and connect the Ethernet port to your Internet router.  Boot your Raspberry Pi into Raspbian (as described in the helpsheet that comes with it), and run:

sudo apt-get install bridge-utils hostapd udhcpd bind9 openvpn

2. Make HostAPD support your Edimax dongle

If, like me, you’re using an Edimax dongle, you need to do an extra couple of steps to make it work as an access point. Skip this bit if you’re using one of the other dongles I listed or if you know better.

wget http://dl.dropbox.com/u/1663660/hostapd/hostapd.zip
unzip hostapd.zip
sudo mv /usr/sbin/hostapd /usr/sbin/hostapd.original
sudo mv hostapd /usr/sbin/hostapd.edimax
sudo ln -sf /usr/sbin/hostapd.edimax /usr/sbin/hostapd
sudo chown root.root /usr/sbin/hostapd
sudo chmod 755 /usr/sbin/hostapd

3. Set up OpenVPN

Get OpenVPN configuration files from your VPN provider: often these will be available under the iOS downloads. There’ll probably be one for each available endpoint. I chose the one for Reyjkavik, because Iceland’s got moderately sensible privacy laws and I’m pretty confident that it would take judicial oversight for British law enforcement to collaborate with Icelandic authorities on getting a wiretap in place, which is the kind of level of privacy I’m happy with. Copy your file to /etc/openvpn/openvpn.conf and edit it: you may find that you need to put your VPN username and password into it to make it work.

sudo service openvpn start

You can now test your VPN’s working, if you like. I suggest connecting to the awesome icanhazip.com and asking it where you are (you can use your favourite GeoIP website to tell you what country it thinks you’re in, based on that):

curl -4 icanhazip.com

Another option would be to check with a GeoIP service directly:

curl freegeoip.net/json/

4. Set up your firewall and restart the VPN connection

Unless your VPN provider gives you DNAT (and even if they do, if you’re paranoid), you should set up a firewall to allow only outgoing connections to be established, and then restart your VPN connection:

sudo iptables -A INPUT -i tun0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
sudo iptables -A INPUT -i tun0 -j DROP
sudo sh -c "iptables-save > /etc/iptables.nat.vpn.secure"
sudo sh -c "echo 'up iptables-restore < /etc/iptables.nat.vpn.secure' >> /etc/network/interfaces"
sudo service openvpn restart

5. Configure your WiFi hotspot

Configure bind as your DNS server, caching responses on behalf of Google’s DNS servers, or another DNS server that you trust. Alternatively, you can just configure your DHCP clients to use Google’s DNS servers directly, but caching will probably improve your performance overall. To do this, add a forwarder to /etc/bind/named.conf.options:

forwarders {
  8.8.8.8;
  8.8.4.4;
};

Restart bind, and make sure it loads on boot:

sudo service bind9 restart
sudo update-rc.d bind9 enable

Edit /etc/udhcpd.conf. As a minimum, you should have a configuration along these lines (you might need to tweak your IP address assignments to fit with your local network – the “router” and “dns” settings should be set to the IP address you’ll give to your Raspberry Pi):

start 192.168.0.2
end 192.168.0.254
interface wlan0
remaining yes
opt dns 192.168.0.1
option subnet 255.255.255.0
opt router 192.168.0.1
option lease 864000 # 10 days

Enable DHCP by uncommenting (remove the hash!) the following line in /etc/default/udhcpd:

#DHCPD_ENABLED="yes"

Set a static IP address on your Raspberry Pi in the same subnet as you configured above (but not between the start and end of the DHCP list):

sudo ifconfig wlan0 192.168.0.1

And edit your /etc/network/interfaces file to configure it to retain this on reboot (you’ll need to use tabs, not spaces, for indentation):

iface wlan0 inet static
  address 192.168.0.1
  netmask 255.255.255.0

And comment out the lines relating to hot-plugging of WiFi adapters/network hopping:

#allow-hotplug wlan0
#wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
#iface default inet manual

Right – onto hostapd, the fiddliest of the tools you’ll have to configure. Create or edit /etc/hostapd/hostapd.conf as follows, but substitute in your own SSID, hotspot password, and channel (to minimise interference, which can slow your network down, I recommend using WiFi scanner tool on your mobile to find which channels your neighbours aren’t using, and use one of those – you should probably avoid the channel your normal WiFi uses, too, so you don’t slow your own connection down with crosstalk):

interface=wlan0
driver=nl80211
ssid=your network name
hw_mode=g
channel=6
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=2
wpa_passphrase=your network password
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP
rsn_pairwise=CCMP

Hook up this configuration by editing /etc/default/hostapd:

DAEMON_CONF="/etc/hostapd/hostapd.conf"

Fire up the hotspot, and make sure it runs on reboot:

sudo service hostapd start
sudo service udhcpd start
sudo update-rc.d hostapd enable
sudo update-rc.d udhcpd enable

Finally, set up NAT so that people connecting to your new hotspot are fowarded through the IP tunnel of your VPN connection:

sudo sh -c "echo 1 > /proc/sys/net/ipv4/ip_forward"
sudo sh -c "echo net.ipv4.ip_forward=1 >> /etc/sysctl.conf"
sudo iptables -t nat -A POSTROUTING -o tun0 -j MASQUERADE
sudo sh -c "iptables-save > /etc/iptables.nat.vpn.secure"

6. Give it a go!

Connect to your new WiFi hotspot, and go to your favourite GeoIP service. Or, if your VPN endpoint gives you access to geographically-limited services, give those a go (you’d be amazed how different the Netflix catalogues are in different parts of the world). And give me a shout if you need any help or if you have any clever ideas about how this magic little box can be improved.

Further reading: