github.com/wangch/gohop

GoHop

GoHop is a VPN implemented in golang, with encryption and obfuscation built in nature. The goal of this project is to escape from censorship and intellegent package inspection.

This is also my network forencics course project.

Why Reinvent the Wheel?

There're already lots of VPN solutions like OpenVPN, L2TP with IPSec, PPTP and other commercial VPNs. But one key problem of these VPNs are that they're only built for anti-censorship instead of anti-GFW, of course, because their developers are not Chinese.

In the past, encrypting packets is enough to get through GFW, but around Nov. 2012, with the upgrading of GFW, where DPI(deep packet inspection) and Macheine Learning was introduced, although they cannot decrypt the packets and see the contents, they can still detect there're HTTP packets encrypted inside VPN packets, thus both OpenVPN and SSH tunnel was blocked in China.

How to Escape from DPI

There's no silver bullet to escape from the intelligent GFW, except for revolution :). All what i'm going to do are temporal solutions.

First, OpenVPN and SSH are both built on top of SSL, which has distinct handshake character and can be easily detected by GFW. Second, all present VPN solutions are single-port or single-protocol, thus the flow can be captured easily and with the help of machine learning, new protocols can be inspected, too.

So I'm going to implement a VPN with these features:

• Pre-shared key based authentication, randomly generated key for encryption. NO SSL, maybe a reinvented SSL :).
• "Frequency hopping"-like port and protocol hopping, both handshake and packet transmission will be acctually done in random port and protocol.
• Traffic shaping to hide protocol's statistical properties.

Implemention

This project will be implemented in golang, a fast, static typed and human-friendly language developed by google. VPN connection will be build on top of Linux's tun/tap device. I have no plan to port it to windows or OS X.

I think it would not be very difficult to port it to OS X. Howerver, I'm not able to develop a OS X edition as I'm not a mac owner. If u wanna help, please fork and send me pull requests, I'd appreciate it.

How To Use

Download

You can get updated release from https://github.com/bigeagle/gohop/releases , go programs are static-linked, so it's very likely that my prebuilt releases can run on your box.

Build and Install

First get dependency libraries and gohop source code.

go get github.com/bigeagle/go-logging
go get github.com/bigeagle/water
go get code.google.com/p/gcfg
go get github.com/bigeagle/gohop

build and install:

go install github.com/bigeagle/gohop

Config and Run

On the server, if u are using it for anti-GFW internet access, ip forwarding is needed:

sysctl net.ipv4.ip_forward=1
iptables -t nat -A POSTROUTING -j MASQUERADE

edit server.ini as your server's config file. Run

gohop server.ini

at client side, edit client.ini as your config file, custom routes is supported so that in-china network packets will not go through gohop. Run

gohop client.ini

wait until u see Connection Initialized, pay attention to your DNS config, if u are using a Chinese DNS server, u're still unable to access blocked websites.

now try to ping twitter.com and cheers :).

LICENSE

Copyright (c) 2013 Justin Wong <[e-mail]>

This program is free software: you can redistribute it and/or modify    
it under the terms of the GNU General Public License as published by    
the Free Software Foundation, either version 3 of the License, or    
(at your option) any later version.    

This program is distributed in the hope that it will be useful,    
but WITHOUT ANY WARRANTY; without even the implied warranty of    
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the    
GNU General Public License for more details.    

You should have received a copy of the GNU General Public License    
along with this program.  If not, see <http://www.gnu.org/licenses/>.