Perpetually in beta, the November 16th version implements a tweaked version of the ZRTP protocol used to set up the encryption of call data between two parties after it has been initiated by SIP. The expanded list of VoIP clients tested now runs to X-Lite, Gizmo, XMeeting, SJphone and, importantly, Google Talk, though Zimmermann said it should support any standards-based client in principle.
Skype now stands alone as the one popular client not supported, but in Zimmermann’s view that is a non-standard universe unto itself. Likewise, it runs on all versions of Windows but has not yet been tested on Vista.
The first Windows beta of Zfone – previously the software had been Apple-only – was launched in, May of 2006 since which it has found its way into a number of third-party products, notably Borderware’s SIPassure VoIP security firewall. Zfone has also been licensed for use in Asterisk voice PBXs, PGP Corporation’s VoIP software, and even mobile phone clients, a potential growth market.
In Zimmermann’s view, the inherent insecurity of VoIP would ensure that encryption such as that provided by Zfone, became unavoidable.
“VoIP is predisposed towards making it easy for anyone to intercept calls,” he said. Where once he had written the PGP encryption program to secure communication from an overbearing state or police, now he saw criminality as the main enemy.
“Organised crime now controls the Internet. Criminals can wiretap [even the] police,” he said. “The whole of VoIP will have to embrace encrypted calls.”
The device of keeping the product in an apparent beta state was a ruse to avoid having to turn it into a supportable product. Zimmermann’s business model derives income from selling the SDK to developers, leaving the client as a free download to spread familiarity.
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