dndx-phantun/README.md

Phantun

A lightweight and fast UDP to TCP obfuscator.

Overview

Phanton is a project that obfuscated UDP packets into TCP connections. It aims to achieve maximum performance with minimum processing and encapsulation overhead.

It is commonly used in environments where UDP is blocked/throttled but TCP is allowed through.

Phanton simply converts a stream of UDP packets into obfuscated TCP stream packets. The TCP stack used by Phantun is designed to pass through most L3/L4 stateful/stateless firewalls/NAT devices. It will not be able to pass through L7 proxies. However, the advantage of this approach is that none of the common UDP over TCP performance killer such as retransmissions and flow control will occur. The underlying UDP properties such as out-of-order delivery are fully preserved even if the connection ends up looking like a TCP connection from the perspective of firewalls/NAT devices.

Usage

Phantun creates TUN interface for both the Client and Server. For Client, Phantun assigns itself the IP address 192.168.200.2 and for Server, it assigns 192.168.201.2. Therefore, your Kernel must have net.ipv4.ip_forward enabled and setup appropriate iptables rules for NAT between your physical NIC address and Phantun's TUN interface address.

Enable Kernel IP forwarding

Edit /etc/sysctl.conf, add net.ipv4.ip_forward=1 and run sudo sysctl -p /etc/sysctl.conf.

Add required firewall rules (using nftables as an example)

Client

Client simply need SNAT enabled on the physical interface to translate Phantun's address into one that can be used on the physical network. This can be done simply with masquerade.

Note: change eth0 to whatever actual physical interface name is

table inet nat {
    chain postrouting {
        type nat hook postrouting priority srcnat; policy accept;
        iifname tun0 oif eth0 masquerade
    }
}

Server

Server needs to DNAT the TCP listening port to Phantun's TUN interface address.

Note: change eth0 to whatever actual physical interface name is and 4567 to actual TCP port number used by Phanton server

table ip nat {
    chain prerouting {
        type nat hook prerouting priority dstnat; policy accept;
        iif eth0 tcp dport 4567 dnat to 192.168.201.2
    }
}

Give Phantun binaries required capability to it can be run as non-root (Optional)

It is ill-advised to run network facing applications as root user. Phantun can be run fully as non-root user with the cap_net_admin capability.

sudo setcap cap_net_admin=+pe phantun_server
sudo setcap cap_net_admin=+pe phantun_client

Start

Server

Note: 4567 is the TCP port Phantun should listen on and must corresponds to the DNAT rule specified above. 127.0.0.1:1234 is the UDP Server to connect to for new connections.

RUST_LOG=info /usr/local/bin/phantun_server --local 4567 --remote 127.0.0.1:1234

Client

Note: 127.0.0.1:1234 is the UDP address and port Phantun should listen on. 10.0.0.1:4567 is the Phantun Server to connect.

RUST_LOG=info /usr/local/bin/phantun_client --local 127.0.0.1:1234 --remote 10.0.0.1:4567

MTU overhead

Phantun aims to keep tunneling overhead to the minimum. The overhead compared to a plain UDP packet is the following:

Plain UDP packet: 20 byte IP header + 8 byte UDP header = 28 bytes Phantun obfuscated UDP packet: 20 byte IP header + 20 byte TCP header = 40 bytes

Phantun's additional overhead: 12 bytes. I other words, when using Phantun, the usable payload for UDP packet is reduced by 12 bytes. This is the minimum overhead possible when doing such kind of obfuscation.

Version compatibility

While the TCP stack is fairly stable, the general expectation is that you should run same minor versions of Server/Client of Phantun on both ends to ensure maximum compatibility.

Compariation to udp2raw

udp2raw is another popular project by @wangyu- that is very similiar to what Phantun can do. In fact I took inspirations of Phantun from udp2raw. The biggest reason for developing Phanton is because of lack of performance when running udp2raw (especially on multi-core systems such as Raspberry Pi). However, the goal is never to be as feature complete as udp2raw and only support the most common use cases. Most notably, UDP over ICMP and UDP over UDP mode are not supported and there is no anti-replay nor encryption support. The benefit of this is much better performance overall and less MTU overhead because lack of additional headers inside the TCP payload.

Here is a quick overview of comparison between those two to help you choose:

	Phantun	udp2raw
UDP over FakeTCP obfuscation	✅	✅
UDP over ICMP obfuscation	❌	✅
UDP over UDP obfuscation	❌	✅
Multi-threaded	✅	❌
Throughput	Better	Good
Raw IP mode	TUN interface	Raw sockets + BPF
Tunneling MTU overhead	12 bytes	44 bytes
Seprate TCP connections for each UDP connection	Client/Server	Server only
Anti-replay, encryption	❌	✅
IPv6	Planned	✅

License

Copyright 2021 Datong Sun dndx@idndx.com

Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option. Files in the project may not be copied, modified, or distributed except according to those terms.