[Cryptography] one-time pads

Philip Shaw wahspilihp at gmail.com
Mon Jan 20 21:42:29 EST 2014


On 21 Jan 2014, at 5:11 , Tom Mitchell <mitch at niftyegg.com> wrote:
> The top to bottom structure of the pad makes them a stream cypher although a
> key in the corner can ID any page so pages can be tossed if the protocol is to
> attach the page key i.e. not "Page 1, 2, 3,.." but a  fixed length
> field  "(C}TEw[;wgU5*2c"
> messages can be sent out of sequence but that implies the pad is busted open
> commonly undesirable with a OTP (at both ends).  Page key tricks are possible.
> 
> After folk address my naive summary above, what does a modern OTP look like?

ISTR reading something about using data tape with a modified reader, so that the tape is erased after it passes through the read head, then over-written multiple times (and then burnt - the overwriting is just to protect against the tapes being intercepted on their way to the incinerator).
Of course, that makes the reader totally obvious to anyone who looked, but IIRC the device was for use inside embassies or similar facilities, so the pads could be transported by diplomatic courier anyway.

I have had the idea of producing something compatible with an SD reader (at least the common open-ended type) but which stores the data embedded inside cardboard or similar material, which can be doped on the outer end with the phosphorous + shielding layer used on strike-anywhere matches, but I haven’t worked out any specifics, and it would probably only be practical to store a KB at most - so useful for a couple of private keys but not much else. It still wouldn’t be deniable, but it would be trivial to destroy in a hurry.
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