[VOIPSEC] zFone

[Jon Callas]

On 12 Sep 2005, at 12:02 PM, Alexander Ph. Lintenhofer wrote:


> Hello everywhere,
>
> I just read about Phil Zimmermanns new invention zFone and would  
> like to
> ask you about your opinion. What do you think about the
> authentication/identification scheme without a PKI?
>
I just got back from vacation, and have been catching up.

I've been working with (near?) Phil on Zfone and will be happy to  
answer questions that I can. I was with him at Black Hat and DefCon,  
and will draw the line at talking about spec details.

I think there are a few things about the way he's done Zfone that are  
extraordinarily important.

First is that he's drawn on principles that worked in the past and  
improved them slightly for VOIP. The mechanism he's using, as Randell  
Jesup noted, is similar to PGPfone and also the AT&T secure phones of  
the early '90s. Zfone combines a simple DH symmetric key transfer  
with biometric authentication. Yes, the three characters the  
participants may use are derived from the key material, they're not  
actually part of it.

The other major thing that I think is nice about this system is that  
by using a chain of hashes of the retained shared secrets, you get  
forward secrecy (which you do not with self-signed certificates)  
while having an authorization chain. You know that the device you're  
talking to is the same device that you were talking to  in previous  
calls. If there is some sort of man in the middle, that attack is  
still present.

I'm happy to answer other questions about the zFone protocols.

     Jon

-- 
Jon Callas
CTO, CSO
PGP Corporation         Tel: +1 (650) 319-9016
3460 West Bayshore      Fax: +1 (650) 319-9001
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