VTun is a networking application which can set up Virtual Tunnels over TCP/IP networks. It supports Internet Protocol

Internet Protocol

The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...

 (IP), Point-to-Point Protocol

Point-to-Point Protocol

In networking, the Point-to-Point Protocol is a data link protocol commonly used in establishing a direct connection between two networking nodes...

 (PPP) and Serial Line Internet Protocol

Serial Line Internet Protocol

The Serial Line Internet Protocol is an encapsulation of the Internet Protocol designed to work over serial ports and modem connections. It is documented in RFC 1055...

 (SLIP) protocols. It exists as the reference implementation of the Tun/Tap

TUN/TAP

In computer networking, TUN and TAP are virtual network kernel devices. They are network devices that are supported entirely in software, which is different from ordinary network devices that are backed up by hardware network adapters....

 user-space tunnel driver which was included in the Linux

Linux

Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

 kernel as of version 2.4, also originally developed by Maxim Krasnyansky. Bishop Clark is the current maintainer.

Networking

Like most other applications of its nature, VTun creates a single connection between two machines, over which it multiplexes all traffic. VTun connections are initiated via a TCP connection from the client to the server. The server then initiates a UDP connection to the client, if the UDP protocol is requested.

The software allows the creation of tunnels, for routing traffic in a manner similar to PPP, as well as a bridge-friendly ethertap connection.

Authentication

VTun uses a Private Shared Key to negotiate a handshake via a challenge and response.

Non-SSL versions

A continual source of concern, and the target of more than one strongly worded security assessment, is that the VTun server and client binary applications can be completely built without SSL

Transport Layer Security

Transport Layer Security and its predecessor, Secure Sockets Layer , are cryptographic protocols that provide communication security over the Internet...

 support. When such binaries are used, the encryption between both endpoints is only a simple XOR cipher, which is completely trivial to decode. This type of build is not supported by the developers.