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From: devine@vianet.UUCP (Bob Devine)
Newsgroups: sci.crypt
Subject: Re: Cheap more-or-less one-time-pads
Message-ID: <182@vianet.UUCP>
Date: Fri, 8-May-87 20:16:21 EDT
Article-I.D.: vianet.182
Posted: Fri May  8 20:16:21 1987
Date-Received: Sun, 10-May-87 01:12:44 EDT
References: <57@decvax.UUCP>
Organization: Western Digital, Boulder Tech Ctr
Lines: 23
Keywords: DES


  I like the idea.  It gave me a grin thinking that somebody from
a spook organization would have to go to a record store looking for the
latest CD by "Prince" or even "Billy and the Boingers"!

> Have I forgotten something?

  One problem would be that the CD doesn't really contain random
bits.  A musical note follows some rules about placement so that the
delta between bytes may be small.  This gives, in essence, a psuedo-
random number because one could predict what the next value taken from
the CD might be.  Repetition also reduces the randomness.  Consider a
Philip Glass composition versus a selection with a wider melodic and
dynamic range.

  This method is not a one-time pad.  You should not reuse that part of
the CD again for a different message.  A destructive read would accomplish
that but then the evidence of what part of a CD is good/bad would help
someone trying to guess what track/sectors were used for a new message.

Bob Devine

PS. What happens if the encrypted data is played backwards? :-)