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
participants (4)
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eichin＠cygnus.com -
technopagan priest -
thug＠phantom.com -
Timothy Newsham