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Re: Streams, Voice, and Sensitive Dependence


14.4 modem, awsome sound quality, 2048 bit DH, 3DES. Have one, love it.


On Fri, 4 Dec 1998, Michael Motyka wrote:

> > It is my understanding that the PGP algorithm is primarily intended
> > as a block cypher.  Therefore, wouldn't an Outer Block stream cypher
> > be more effective for phone conversations?  Both solutions require 
> > hardware for a practical (tolerably noiseless) implementation, so 
> > there's nothing to be gained by streaming data into a block format.
> >
> Unless you have a really fast ( 1 Mbit / s? ) data connection you're
> going to want to do some voice compression. The algorithms I've seen
> break the audio into discrete time frames and (de)compress frame by
> frame. As a point of reference say about 16 bytes for every 33 msec of
> voice. Quality roughly follows data rate, of course. This makes a block
> cipher seem not so unreasonable.
> Block cipher or stream cipher, either way you're going to have to
> introduce a latency of _at_least_ a couple of frames to allow for
> resends or deliberate out-of-order frame transmission. This makes the
> block cipher look like the better choice.
> I think that using HW voice compression and a 33.6 modem you could get a
> full duplex secure conversation over POTS with a latency in the 0.1 -
> 0.3 second range and a direct cost in the vicinity of $100. With a
> reasonably quick microP any encryption method could probably be done as
> SW.
> This is not a particularly difficult device to build. Any fine US
> citizens want to build some prototypes? 
> Mike

-- Lucky Green <[email protected]> PGP v5 encrypted email preferred.