Philip Zimmermann, best known as the developer of the Pretty Good Privacy (PGP) encryption algorithm, has released a new public beta of a software package designed to encrypt VoIP calls.
Zfone uses Diffie-Helman to generate a per-session key for IP Telephony calls using a protocol called ZRTP, that Zimmermann says is superior to other approaches.
"[ZRTP] achieves security without reliance on a PKI (Public Key Infrastructure), key certification, trust models, certificate authorities, or key management complexity that bedevils the email encryption world," Zimmermann explains.
"It also does not rely on SIP (Session Initiation Protocol) signaling for the key management, and in fact does not rely on any servers at all. It performs its key agreements and key management in a purely peer-to-peer manner over the RTP (Real-time Transport Protocol) packet stream. It interoperates with any standard SIP phone."
The software also works as a separate download that adds encryption features to VoIP programs such as Gizmo and SIPphone. It doesn't interoperate with Skype, which utilises a separate (and proprietary) encryption algorithm. Zimmermann has submitted the ZRTP to the IETF as a proposed public standard. As with PGP, he has published the source code of Zfone for peer review.
Beta versions of Zfone suitable for either Mac OS X, Linux and Windows XP platforms are available for download at no charge here (registration required).
The timing of the release, which adds Windows support not available in earlier versions of Zfone, coincides with controversy over the US government's electronic surveillance efforts. Zfone won't interfere with traffic analysis (involving data on who called who and when), but it does protect the content of conversations against eavesdropping. Zimmermann hopes to license the technology.
In the 1990s, Zimmermann successfully fought a three-year legal battle with the US Government over accusations that his PGP email encryption program breached export controls. Although the Federal Communications Commission has pushed though regulations (in particular the Communications Assistance for Law Enforcement Act (CALEA) that compel VoIP service providers to allow the lawful interception of VoIP calls these regulations don't currently extend to software packages, such as Zfone, that encrypt IP telephony calls between individual computers.
"From the FCC's perspective you can't regulate point-to-point communications, which I think will let Phil off the hook," said Marc Rotenberg, director of the Electronic Privacy Information Centre told the New York Times. ®