On 1/1/06, J.A. Terranson <measl@mfn.org> wrote:
... Is there radioactive material which has has a known property that can be reliably and repetitively measured, that is useful as either a key or a seed, and that is guaranteed to change on a known schedule in a significant (i.e., keying data no longer relevant) way?
The idea being something like msg xor radioseed "keys" = plaintext, but after 30 days, radioseed is different (and the original not knowable), and therefore message is dead.
it seems like this should be possible using a radioactive material with a known short half-life and exposing it to a neutron source with a mask (beryllium?) with the key space on it. assume a grid of cells on a flat surface containing the radioactive material; if a given cell emits over a threshold of radiation it is a '1' bit, dead it is a 0 bit. exposing the 0's to a neutron emitter would fission the radioactive cells early leaving it's ionizing radiation level below the threshold. there would be some delay between when the key was usable with all cells/bits readable (a few days, weeks, months?) and when it was still holding a detectable / useful amount of key information that could be used in a brute force attack against the unknown bits of key. they let you put americium in smoke detectors but something tells me it would be hard to get radioactive crypto keys commercially approved for production. :) (the neutron source would be another problem, although piezoelectric fusion might work)