Hmm...hardware secure phone?

I've been reading up on Codecs.  Motorola has the MC145505 PCM Codec
which samples at 8khz and the PCM output is at 64kbps.  We can then
use the MC145532 ADPCM Transcoder to reduce the data stream to
16kbps.  With the breaks in spoken languages, perhaps we could get
this to compress just enough to go through a 14.4 kbps modem.

Anyway, who knows of a DES or RSA chip which will do 16kbps?
Then all we need is a microcontroller to run the show, and 
perform D-H or RSA key exchange.

-Thomas

> 
> 
> I've been reading up on Codecs.  Motorola has the MC145505 PCM Codec
> which samples at 8khz and the PCM output is at 64kbps.  We can then
> use the MC145532 ADPCM Transcoder to reduce the data stream to
> 16kbps.  With the breaks in spoken languages, perhaps we could get
> this to compress just enough to go through a 14.4 kbps modem.
> 
> Anyway, who knows of a DES or RSA chip which will do 16kbps?
> Then all we need is a microcontroller to run the show, and 
> perform D-H or RSA key exchange.
> 
> -Thomas
> 

with a DSP chip you can compress voice down to the
4.8kbps to 9.6kbps range with CELP
the 400 bps to 4800 bps range with LPC

If you have enough cycles and memory left over afterwards
you can do DES on the same DSP (depending on which brand you
choose this may or may not be feasible).

If you are using a host computer the computer can do
DES and framing for you.

>> Anyway, who knows of a DES or RSA chip which will do 16kbps?
>> Then all we need is a microcontroller to run the show, and 
	(kbits? kbytes?) Well, a quick check of some C code gets me
200Kbytes[*] (1.6Mbits) per second on a SparcStation ELC. I'll have
numbers for the i960 microcontroller[**] later this weekend -- you
might be able to have the microcontroller do the encryption too :-)
							_Mark_

[*] That's 50,000 calls to des_ecb_encrypt and 50,000 calls to
des_ecb_decrypt, so 100K ecbs, each ecb is 8 bytes, so that's 800K
bytes, and it took 3.98 user CPU seconds, so that's 200K bytes. Yep,
the math checks. Compiler: Solaris gcc -O (a few months old); DES
code: Ferguson's, as folded into Kerberos 4.

[**] Yeah, it's marketed as a microcontroller. If you put it in a
toaster, you wouldn't need a heating element. Still, it's part of the
background for my talk at the Embedded Systems conference in October
on "Security Issues in Embedded Networking".

> I've been reading up on Codecs.  Motorola has the MC145505 PCM Codec
> which samples at 8khz and the PCM output is at 64kbps.  We can then
> use the MC145532 ADPCM Transcoder to reduce the data stream to
> 16kbps.  With the breaks in spoken languages, perhaps we could get
> this to compress just enough to go through a 14.4 kbps modem.

How about just feeding the 16kbps stream to either a DES chip or a
microcontroller programmed for IDEA encryption/decryption?  And don't
even bother with 14.4.  Zyxel modems can do 16.8 & 19.2kbps full duplex.
But Zyxel's modulation is proprietary.  A new standard called v.32terbo
has emerged which standardizes 16.8 and 19.2 modulation - I believe some
of AT&T's new modems support v.32terbo.  Down the road a bit 21.6, 24.4 & 28.8
modulation (v.FAST) will be more common.  The way I see it, the hassle of
squeezing 16kbps into a 14.4kbps bandwidth pipe is not worth the agrivation
when you can pipe it straight into a Zyxel or v.32terbo modem right now.

> Anyway, who knows of a DES or RSA chip which will do 16kbps?

They all do, some chips even go as high as several megabits per second for
DES.  I don't know of any chips that do RSA though.

> Then all we need is a microcontroller to run the show, and 
> perform D-H or RSA key exchange.

Exactly.


---
thug@phantom.com