From: "Dave Emery" <die@pig.die.com>
Date: Fri, 2 Dec 94 18:59:25 PST
To: cypherpunks@toad.com
Subject: Re: recent voice over data (fwd)
Message-ID: <9412030231.AA01795@pig.die.com>
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From die Thu Dec  1 20:54:10 1994
Subject: Re: recent voice over data
To: eric@remailer.net (Eric Hughes)
Date: Thu, 1 Dec 1994 20:54:10 -0500 (EST)
From: "Dave Emery" <die@pig.die.com>
Reply-To: die@die.com
In-Reply-To: <199412020157.RAA14321@largo.remailer.net> from "Eric Hughes" at Dec 1, 94 05:57:18 pm
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> 
>    From: "Dave Emery" <die@pig.die.com>
> 
> 	   I can't quite see how this would work unless the voice was run
>    at a very low level relative to the data.  
> 
> I believe there are also maximum rates on the data when used with
> voice (4.8 kbps?) and the modulation doesn't use echo cancellation.
> 
> 
	This whole thing has an interesting security consequence -
retrieving the voice under data off a crude alligator clip type 2 wire
wiretap may be difficult because it requires knowing the data going in
both directions.  So if one sends random or cryptographically secure
pseudo random data one might be able to do a reasonable job of hiding
the voice channel from simple wiretapping technology even though it is
analog rather than digital.  And generating random data with a noise
diode and a UART is easy to do and very secure. 

	It is already known that retrieving both streams of data from a
two wire tap (voltage only) when neither data stream is known or
predictable is difficult or even nearly impossible to do with modern
near-end-echo cancelling modem modulations such as V.32 and V.34, and
without this capability the voice would almost certainly not be
intelligable over the roar of the modem tones. 

	Granted this is not the kind of security one gets from strong
encryption, but it is easy to do and makes wiretapping a lot harder.... 
If I were concerned with securing my calls from most threats other than
the TLA's I think spending 640 bucks for two of these modems and a
little box with a UART and a noise diode might be a cheap and dirty
voice privacy hack.  Certainly it would defeat the idly curious and the
private eye divorce investigator types... 

						Dave Emery N1PRE

	(PGP signature out for repair)