http://www.starium.com 14.4 modem, awsome sound quality, 2048 bit DH, 3DES. Have one, love it. --Lucky 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 <shamrock@cypherpunks.to> PGP v5 encrypted email preferred.