kadie@uiucdcsb.cs.uiuc.edu (02/13/88)
Could a one time pad be used to make a spy tape recorder or camera?
It would work like this. At the spy's home base two identical
(digital?) tapes are make containing random noise. Then the spy goes
into the field with one tape recording things
by XORing information onto the tape.
If he is every stopped the tape looks completely random so no one
can prove that he was spying or tell what he recorded.
If the mission is successful he sends the tape back to
base where they decode it with the other tape.
Carl Kadie
Inductive Learning Group
University of Illinois at Urbana-Champaign
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ARPA: kadie@M.CS.UIUC.EDU (kadie@UIUC.ARPA)henry@utzoo.uucp (Henry Spencer) (02/15/88)
> If he is every stopped the tape looks completely random so no one > can prove that he was spying or tell what he recorded. Nobody can tell what he recorded, true. But the possession of tapes full of random noise (note, this is not what is found on a blank tape!) is itself highly suspicious. How would he explain it? Remember too that it is almost impossible to conceal spying well enough to fool careful surveillance, once the opposition is suspicious (if they catch you photographing military maneuvers, they don't need to look at the film to know what you were up to). -- Those who do not understand Unix are | Henry Spencer @ U of Toronto Zoology condemned to reinvent it, poorly. | {allegra,ihnp4,decvax,utai}!utzoo!henry
pwallich@caen.engin.umich.edu (Paul Wallich) (02/28/88)
In article <161200004@uiucdcsb>, kadie@uiucdcsb.cs.uiuc.edu writes: > > Could a one time pad be used to make a spy tape recorder or camera? > > It would work like this. At the spy's home base two identical > (digital?) tapes are make containing random noise. Then the spy goes > into the field with one tape recording things > by XORing information onto the tape. > Apparently this was done during WWII using records for secure radio conversations between allied heads of state: random noise was pressed onto two phonograph discs and used to modulate the signal carrying the conversation, then demodulate on the other side. This was analog, so synchronization was a problem. I expect if it was done then, it's done now, only more fun. pw
kludge@pyr.gatech.EDU (Scott Dorsey) (03/01/88)
>In article <161200004@uiucdcsb>, kadie@uiucdcsb.cs.uiuc.edu writes: >> It would work like this. At the spy's home base two identical >> (digital?) tapes are make containing random noise. Then the spy goes >> into the field with one tape recording things >> by XORing information onto the tape. Sperry made a machine during the cold war which had a transmitter with a reel of tape, whose synchronous motor had a local oscillator. Incoming voice was mixed with the tape noise such that the S/N ratio was less than one, and then this signal was mixed with the motor synch signal (a square wave, more or less), and transmitted. The receiver filtered off the synch frequency and drove another tape drive motor with it. Then the second tape was subtracted from the composite frequency. This didn't work very well. Channel noise would cause the system to lose synchronization, and the task of synching the tapes up at the beginning was tedious. It's still in use, though I don't know why. Scott Dorsey Kaptain_Kludge SnailMail: ICS Programming Lab, Georgia Tech, Box 36681, Atlanta, Georgia 30332 "To converse at the distance of the Indes by means of sympathetic contrivances may be as natural to future times as to us is a literary correspondence." -- Joseph Glanvill, 1661 Internet: kludge@pyr.gatech.edu uucp: ...!{decvax,hplabs,ihnp4,linus,rutgers,seismo}!gatech!gitpyr!kludge