Compressed/Encrypted Voice using Modems

[thug@phantom.com (Murdering Thug)]

Perry E. Metzger writes:
> It occured to me that some people might not get the significance of all
> this, so prehaps I ought to amplify. 
> 
> With the ability to compress speech down into the
> same baud rate as, say, a V.32 modem, all one would have to do to have
> perfectly secure voice communications is replace your phone with a
> setup that took in your speech, digitized it, compressed it, encrypted
> it, and sent it over the modem to the other side where this would be
> inverted. Fast enough software compression of voice would mean any PC 
> with a DSP card and a V.32 modem could become an unbreakable scrambler.
> The chief problem is that the DSP needed to do decent compression is
> very crunchy, and encryption also tends to be crunchy, so there aren't
> typically enough cycles on your average PC. Of course, were someone to
> commercially market a board that did all this in hardware...

This is a device waiting to be built, if it has not been built already.
I would estimate that a pair of such stand-alone encrypted telephones can
be built for under $2000 and about a month or two of development time.

And why are you limiting this to V.32 (9600bps)?  V.32bis (14.4k bps) modem
chips cost maybe 20% more than v.32 chips in quantity.

Even higher speeds are available if you're willing to go that far.  Zyxel
v.32bis modems have proprietary 16.8 kbps and 19.2 kbps full duplex raw
modulation rates, but they use DSPs instead of modem chips like the
ones from Rockwell, AT&T, and Intel.  I believe there are some v.FAST
(not CCITT compliant) modems like the one's from Motorola (Codex) that
can do 21.6 kbps and 24.0 kbps.  I believe the final speed of v.FAST once
standardized by the CCITT will be 28.8 kbps.

Even so, if CEPT coding provides somewhat intelligeable speech at 4800 bps,
then I am sure the sound quality at 14,400 bps is at least as good as
regular analog telphone conversations when it comes to voice.

Consider a device that uses this: 

       A. a dedicated CEPT codec chip if they currently exist
            OR
          a DSP chip programmed for CEPT compression coding/decoding 

       B. a high-speed dedicated DES chip
            OR 
          a RISC microcontroller (i960/amd29k) to do IDEA or LOKI 

       C. a quality UART like the Zilog SCC or National 16550AFN 

       D. an external 14,400 bps modem ( v.42 & v.42bis turned off)

                  _____         _____         _____          _____
  earpiece <-----|     |       |     |       |     |        |     | 
                 |     |  bus  |     |  bus  |     | RS-232 |     |
                 |  A  |-------|  B  |-------|  C  |--------|  D  |-----: RJ-11
                 |     |       |     |       |     |        |     |       jack 
mouthpiece >-----|_____|       |_____|       |_____|        |_____| 
                                                |
                                                |
                                           dialing keypad
                                         on/off-hook switch
                                             circuit

Of course, if the FBI's Digital Telephony act passes it would be illegal to
sell such devices if they do not have a back door.  HOWEVER, it would not
be illegal to build such devices for personal use.  Hence, one may publish
the schematics and DSP/microcontroller source code to such a device and
let people build them themselves.  However, the masses would not benefit
from this.  Only those with the skills or those with the money (mafia/drug
lords) to pay those with the skills, would be able to produce such devices
for their own use.  The FBI's proposal would not stop the people they want
to catch most from using encryption.  The FBI is wasting their time, and
taking away our rights for no good reason.

I assume a black market for such devices as the above already exists and
will expand massively as the price of DSPs and RISC microcontrollers
drops.  The logical end result would be to put this whole device onto a
single VLSI chip, and selling such crypt-phones for $100-200 a pop to the
mases, but there's a snowballs chance in hell of that happening if the world's
governments have anything to do with it.


Thug