NetNews Usenet Archive 1992 #26/NN_1992_26.iso/spool/sci/crypt/4566

Text File | 1992-11-10 | 1.7 KB | 37 lines

Newsgroups: sci.crypt
Path: sparky!uunet!shearson.com!snark!pmetzger
From: [e-mail] (Perry E. Metzger)
Subject: Re: Encrypted phones, keys, taps, ...
Message-ID: <[e-mail]>
Sender: [e-mail] (News)
Organization: /usr/local/lib/news/organization
References: <[e-mail]> <[e-mail]> <[e-mail]>
Date: Tue, 10 Nov 1992 21:36:02 GMT
Lines: 25

[e-mail] (Luis Ola Toshio Chi-Ming) writes:
>In article <[e-mail]> [e-mail] (Perry E. Metzger) writes:
>>Its all really easy. CELP compression can be done with cheap DSPs --
>>you can buy the code if you don't feel like writing it yourself. The
>>encryption can be done an order of magnitude faster than you need even
>>on conventional processors.  V.32bis modem modules are a dime a dozen.
>>You don't need to be AT&T to do this -- any talented EE with a few
>>weeks of work could put a system to do this together.
>
>Can someone tell me how these digitally encrypted phones provide
>reasonable security in light of the following problem.  Phones lines
>can tolerate raw data rates of 9.6 kbps whereas voice requires
>64 kbps.  Let's say the CELP compression reduces the voice
>requirement down to 9.6 kbps (voice becomes noticibly choppy thereafter).
>Where do they allocate the bandwidth needed for sycronization and error
>correction.

CELP produces very good voice at 4800 bits/second. V.32bis does
14kbits/sec very reliably. Does this answer you questions?

--
Perry Metzger        [e-mail]
--
"They can have my RSA key when they pry it from my cold dead fingers."
Libertarian Party info: Phone [phone], E-Mail [e-mail]