Secure Voice over IP: Zfone

ronjor · Mar 14, 2006

About the new Zfone Public Beta Software

Some of you may remember my PGPfone product from 1996, back when the Internet wasn't ready for telephony. No one had broadband, and there were no standard protocols for Voice over IP (VoIP). What a difference a decade makes. Zfone is like PGPfone, but brought up to date with all the modern VoIP protocols, such as SIP and RTP.
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Mac and Linux at this time.

philzimmermann.com

nameless · Apr 3, 2006

Zfone is in beta

I just read this article:

http://www.wired.com/news/technology/0,70524-0.html

I tried opening the link it points to:

http://www.philzimmermann.com/EN/zfone/index.html

But I can't even resolve philzimmermann.com to an IP address. Neither can a friend of mine on the other side of the United States.

Can anyone access philzimmermann.com?

aigle · Apr 3, 2006

Re: Zfone is in beta

The link is down for me, in Saudi arabia.

nicM · Apr 3, 2006

Re: Zfone is in beta

Nothing for me too.

Alphalutra1 · Apr 3, 2006

Re: Zfone is in beta

I can access it without a problem, but I have Treewalk DNS which a free personal DNS server with a root extension installed so I can resolve almost every web page created that my isps either don't have or don't want me to access

Here is the text of the web page

Philip Zimmermann

Secure Voice over IP: Zfone

14 Mar 2006 - I've just released Zfone, a new product that takes a new approach to make a secure telephone for the Internet. Zfone lets you whisper in someone's ear, even if their ear is a thousand miles away.

I think it's better than the other approaches to secure VoIP, because it achieves security without reliance on a PKI, key certification, trust models, certificate authorities, or key management complexity that bedevils the email encryption world. It also does not rely on SIP 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 packet stream. It interoperates with any standard SIP phone, but naturally only encrypts the call if you are calling another Zfone client. This new protocol has been submitted to the IETF as a proposal for a public standard, to enable interoperability of SIP endpoints from different vendors.
How to get the Zfone Public Beta

To get your hands on the Zfone public beta software, click here:
Get Started with Zfone Now!

In keeping with the long-standing PGP tradition, the source code is also available to download for peer review.

The Zfone public beta is available today for Mac OS X and Linux. The Windows XP version will be available in mid-April. We'll update this page when we have the Windows version ready. In the meantime, we suggest you don't wait for the Windows version. Give the Mac version a try, just to see it work.
About the new Zfone Public Beta Software

Some PGP aficionados may remember my PGPfone product from 1996, back when the Internet wasn't ready for telephony. No one had broadband, and there were no standard protocols for Voice over IP (VoIP). What a difference a decade makes. Zfone is like PGPfone, but brought up to date with all the modern VoIP protocols, such as SIP and RTP.

In the future, the Zfone protocol will be integrated into standalone secure VoIP clients, but today we have a software product that lets you turn your existing VoIP client into a secure phone. The current Zfone software runs in the Internet Protocol stack on any Windows XP, Mac OS X, or Linux PC, and intercepts and filters all the VoIP packets as they go in and out of the machine, and secures the call on the fly. You can use a variety of different software VoIP clients to make a VoIP call. The Zfone software detects when the call starts, and initiates a cryptographic key agreement between the two parties, and then proceeds to encrypt and decrypt the voice packets on the fly. It has its own little separate GUI, telling the user if the call is secure. It's as if Zfone were a "bump on the cord", sitting between the VoIP client and the Internet. Think of it as a software bump-on-the-cord. Maybe a bump in the protocol stack.

There is also a Zfone SDK for VoIP client developers to integrate this protocol into their VoIP clients, for both software and hardware VoIP clients. The software is implemented in C.
Zfone protocol as a public IETF standard: ZRTP

The protocol we developed for Zfone to set up the cryptographic key agreement is called ZRTP. Alan Johnston, Jon Callas, and I have submitted an IETF Internet Draft for the ZRTP protocol. Alan co-authored RFC 3261 which defines the SIP standard, and Jon is CTO at PGP Corp.

You can view the current state the ZRTP Internet Draft here, in either PDF, text, or HTML format.
Why is Zfone better?

If you are not a crypto geek, you might want to skip this part.

The ZRTP protocol has some nice cryptographic features lacking in many other approaches to VoIP encryption. Although it uses a public key algorithm, it does not rely on a public key infrastructure (PKI). In fact, it does not use persistant public keys at all. It uses ephemeral Diffie-Hellman with hash commitment, and allows the detection of man-in-the-middle (MiTM) attacks by displaying a short authentication string for the users to read and compare over the phone. It has perfect forward secrecy, meaning the keys are destroyed at the end of the call, which precludes retroactively compromising the call by future disclosures of key material. But even if the users are too lazy to bother with short authentication strings, we still get fairly decent authentication against a MiTM attack, based on a form of key continuity. It does this by caching some key material to use in the next call, to be mixed in with the next call's DH shared secret, giving it key continuity properties analogous to SSH. All this is done without reliance on a PKI, key certification, trust models, certificate authorities, or key management complexity that bedevils the email encryption world. It also does not rely on SIP 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 packet stream.

If you have more questions about the ZRTP protocol, see our Zfone FAQ page.
Zfone in the Press

Here are some press articles on the project.

Wired News: Privacy Guru Locks Down VOIP
Associated Press: PGP Inventor to Encrypt Net Calls
eWeek: Privacy Pioneer Promises Secure VOIP
TechWorld: Encryption guru returns with VoIP software
CNET News: Encryption pioneer expands on VoIP plans
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Alphalutra1

nameless · Apr 3, 2006

Re: Zfone is in beta

Thank you, everyone, for checking and posting back. I had a friend in Europe try, and he couldn't access it either, earlier.

I have to tone down my cynicism a bit, I guess... I started thinking the US government was up to no good. But seriously, given the past relationship between the government and Phil Zimmermann, it doesn't seem that far-fetched, does it?

In any case, I can access the site now. Temporary glitch, I guess.

(Personal DNS server? Interesting!)

ErikAlbert · Apr 4, 2006

Re: Zfone is in beta

aigle said:

The link is down for me, in Saudi arabia.
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Some links are down for me too on a regular base, but if I try them on a different time, they work. Don't ask me why.

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