in reply to Re: Unbreakable crypto
in thread Unbreakable crypto

One time pads are the only information theoretically secure cipher. Of course, the devil's in the details. The key has to be truly random. There is the issue of key exchange. But, once you meet these requirements, there is no way to break a one time pad. All possible decryptions with the same length as the message are equally likely, so how do you know that you know that a given 6-letter string decrypts to "rob_au" vs "chester"?

thor

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Re^3: Unbreakable crypto
by Roy Johnson (Monsignor) on May 19, 2004 at 14:52 UTC
    Because "chester" is 7 letters?
    The PerlMonk tr/// Advocate
[reply]
      If you want to be a stickler for the "details", I suppose you're right. But what you didn't see was there was a NUL at the end of "rob_au", thus making it seven characters. ;)

      thor

[reply]
        And "6-letter string" was the encoded form of "7-letter string"? ;-P
        The PerlMonk tr/// Advocate
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Re: Re: Re: Unbreakable crypto
by hardburn (Abbot) on May 19, 2004 at 16:42 UTC

    All possible decryptions with the same length as the message are equally likely

    This is one property of OTPs that I think is often overlooked for practical applications. This could be used for plausible deniability reasons. For instance, say you took the source code to a DeCSS program and a letter to your Grandma, which are both exactly the same length. You then generate a random string of characters, also of the same length. There exist two seperate OTP keys for that character stream, one of which will decrypt the stream into the DeCSS source and the other into the letter. Generating these keys is as simple as XOR'ing the stream against the document. If you get caught, you can give the authorities the key for the letter, and they thus have no evidiance. You can then walk away and give your freinds the key for the source code.

    ----
    send money to your kernel via the boot loader.. This and more wisdom available from Markov Hardburn.

[reply]
      If you get caught, you can give the authorities the key for the letter, and they thus have no evidiance.
      Until they knock on your door and politely ask you to hand over all your computer equipment.
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In Section Obfuscated Code