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From: newton2@ucbtopaz.CC.Berkeley.ARPA
Newsgroups: net.crypt
Subject: Analog time-segment voice scramblers-- How Secure?
Message-ID: <648@ucbtopaz.CC.Berkeley.ARPA>
Date: Wed, 16-Jan-85 13:39:51 EST
Article-I.D.: ucbtopaz.648
Posted: Wed Jan 16 13:39:51 1985
Date-Received: Fri, 18-Jan-85 02:19:05 EST
Organization: Univ. of Calif., Berkeley CA USA
Lines: 25

This is a renewed request for discussion/comment/pointers on the
subject of speech scramblers which work by temporily shuffling blocks
of speech.

If we assume the underlying cryptography to be secure (i.e. the generation
of scramble-sequences throughout the message cannot be anticpated wihout
the key), what are the techniques for cracking the system by direct assault
on the analog scrambled signal? How quickly can this be done- Real time?

I assume a digital random access memory- no clues from the differing noise
level along the length of an analog shift register. However, there might
be clues from the excitation of the (known) impulse response of the band-limited
voice channel. And of course the cleartext (voix humaine) has some known
characteristics.

Is such a scrambler of *any* value against a determined opponent-- i.e.,
might it provide at least some time-limited security or require such special
equipment for routine cracking that the use of large numbers of such scramblers
might overwhelm a particular opponent (not knowing which messages were high-value?)

I'd greatly appreciate any discussion of this, public or private.

Thanks-

		Doug Maisel  415 549-1403