newton2@ucbtopaz.CC.Berkeley.ARPA (01/16/85)
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
henry@utzoo.UUCP (Henry Spencer) (01/20/85)
I'm not an expert on this stuff, but my general impression is that no
analog scrambler is really considered particularly secure. There is
so much redundancy in a voice that it's almost impossible for an analog
system to hide it all from would-be eavesdroppers.
--
Henry Spencer @ U of Toronto Zoology
{allegra,ihnp4,linus,decvax}!utzoo!henry