From: wcs@anchor.ho.att.com (bill.stewart@pleasantonca.ncr.com +1-510-484-6204)
Date: Sun, 13 Mar 94 00:29:14 PST
To: unicorn@access.digex.net
Subject: Re:  Voice encryption
Message-ID: <9403130828.AA16685@anchor.ho.att.com>
MIME-Version: 1.0
Content-Type: text/plain


The problem with secure voice systems isn't doing the encryption,
which is relatively easy; it's designing a voice compression system
that's cheap enough and fast enough to work with the class of modems
you're willing to use.  28.8 kbps modems are now available, using the
Rockwell V.FC stuff until V.FAST gets stablized, but there are concerns
about whether they'll perform well over international circuits,
which are obviously one of the prime markets for secure voice.
If you're willing to standardize on thise, you can get by with a number
of cheap voice-compression algorithms at 16-24 kbps, but standardization
really is somewhat important, as is cost for the consumer market.

One of the speakers at today's BayArea cypherpunks meetings was
talking about a prototype secure voice phone he's building,
with a target price under $1000 for a bump-in-the-cord design.
He had an alpha-quality board with him, blue wires and all,
and was working on refining the design.  Reasonably common DSP parts,
Rockwell modem chip.  One difficulty of the bump-in-the-cord design
is you've got to include phone interfce circuitry, and deal with questions
of whether to provide ringing voltage to the phone (90V has safety
issues as well as circuit cost) or just provide a cheap speaker ringer.
He was looking at Diffie-Hellman for key exchange for simplicity,
(which you can afford to license if you're doing a reasonable-sized run
of phones, though he hadn't negotiated prices.)  The user interface
was nice and simple - 3 LEDs and a "GO Secure" button, and the phone
was designed to let you answer and originate calls in either secure or
aalog-non-secure modes (maybe also digital-non-secure?) for convenience.

Phil Zimmerman is working on a voice-PGP, but I don't know what he's
doign in any detail.

	Bill
# Bill Stewart  AT&T Global Information Solutions, aka NCR Corp
# 6870 Koll Center Parkway, Pleasanton CA, 94566 Phone 1-510-484-6204 fax-6399
# email bill.stewart@pleasantonca.ncr.com billstewart@attmail.com
# ViaCrypt PGP Key IDs 384/C2AFCD 1024/9D6465