And what if I will use FM receiver, tuned on some channel where is the noise. If the potentional attacker don't know the what channel was tuned, he is not able to reproduce this IMHO. Of course, maybe it is possible to record the whole spectrum to tapes, but I think that the noise will change when recorded and played back from tape.

It might possibly be random enough, especially if you use a tape recorder of a reasonably poor quality, thus inducing wow and flutter noise to the recording before it is sampled. anyone else care to comment? Datacomms Technologies web authoring and data security Paul Bradley, Paul@fatmans.demon.co.uk Paul@crypto.uk.eu.org, Paul@cryptography.uk.eu.org Http://www.cryptography.home.ml.org/ Email for PGP public key, ID: 5BBFAEB1 "Don`t forget to mount a scratch monkey"