GNU Free Call: An open source Skype alternative

There's no denying that Skype is by far the most ubiquitous VoIP service today, but a new project launched this week aims to create an open source alternative.

GNU Free Call, which was announced on Monday by the GNU Project, will offer a service that's both secure and usable on all platforms, much the way closed-source Skype is, its developers say. The key difference, however, will be that it's available "without requiring a central service provider to register with, without using insecure source secret binary protocols that may have back-doors, and without having network control points of any kind that can be exploited or abused by external parties," its creators say.

Rather, GNU Free Call will offer what they call "a self organizing meshed calling network," thereby eliminating potentially vulnerable service control points and ensuring the continuation of emergency services even if the existing communication infrastructure has been disrupted.

The SIP Protocol

To make all that possible, GNU Free Call will use the Session Initiation Protocol (SIP), an Application Layer signaling protocol that's designed to be independent of the underlying transport layer.

Specifically, it will build upon the existing GNU SIP Witch VoIP server, which operates without introducing a central point through which communications can be intercepted or captured. GNU SIP Witch also requires minimal system resources, making it suitable even for low-end embedded routers.

GNU SIP Witch is already packaged in a number of popular Linux distributions, including Ubuntu and Fedora, but it can also be built on most BSD systems from source, and it supports compilation on Microsoft Windows as well, according to the GNU Free Call project.

"We will extend SIP Witch to become aware of peer nodes by supporting host caches, and then support publishing of routes to connected peers," the project explains. Host caches are a mechanism used in older P2P networks and are easy to implement, it adds.

Desktop and Mobile GUIs

SIP Witch will also operate as a SIP mediation service for desktops users and IP-enabled cell phones including those running Android. Accordingly, part of the project's plan is to build desktop and mobile GUIs that allow users to monitor the progress of their calls.

In addition, the project will extend SIP Witch to offer secure VoIP proxy, thus allowing any existing SIP-compliant device to establish a secure connection with another such device running SIP Witch at the destination.

For security, uniquely generated keys will protect each communication session, and GNU Privacy Guard -- a free implementation of the OpenPGP standard -- will automate session validation.

eHealth Applications

GNU Free Call could be valuable for "many ordinary public service uses, such as the delivery of eHealth services, as well as medical, and legal communication, where it is essential to treat all with equal human dignity by maintaining privacy regardless of race, religion or political affiliation," the project notes. "Equally important is the continuation of emergency medical services even when existing infrastructure is no longer available or has been deliberately disabled."

The project invites anyone interested to help through its GNU Telephony wiki site. There's also a SIP Witch mailing list and a privacy-focused list for discussing core architecture, privacy issues and social consequences.

Open source technologies offer numerous advantages for business users, as I've already noted. But the security, public safety and intervention-proof aspects of GNU Free Call make it particularly intriguing. This is definitely one to watch.

Follow Katherine Noyes on Twitter: @Noyesk.