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Re: Who needs time vaults anyway?
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> Can anyone explain what use this theoretical "time-sensitive" crypto
> box would be good for?
> Suppose you die.
Hey! Who do you think you are?
Just kidding. When I woke up this morning I realized what I was
missing: the decryption might be out of your hands, such as when
you die, or you might *want* it to be out of your hands for some
With that in mind, I can think of only one unalterable lower-limit
on the time of as decryption-- the speed of light. Suppose you
encrypt your data with successive layers of keys, K1-Kn. Then you
encrypt each key with its predecessor, encrypting Kn with Kn-1,
encryping Kn-1 with Kn-2, etc. Destroy all copies of unencrypted
keys except for K1, which has not been encrypted. Now put all
odd-numbered keys in location A and all even-numbered keys in
location B, which is 1 light minute from location A. Once an agent
has received Key 1, it will take at least n minutes to decrypt
the data. Of course, the agent could just take copies of all of the
keys from location B on some physical media and transport the media
to location A, which would make the lower bound on time to be "much
longer than 1 minute".
Hm. Suppose the n different keys are in n different physical
locations, and the agent does not know where the k+1 location is
until he decrypts the material at the k location. The "scavenger
hunt" scheme for timed decryption. Of course this doesn't mean that
you have to bury your crypto box and make a map with an "X" marking
the spot. Each key could be held by a crypto box which is
publically accessible on the Net. The important thing is that
the decrypting agent can't retrieve the k+1 piece until he has
decrypted the k piece. Then the lower bound on time of decryption
is... um... Well it depends on the location of the decrypting agent
with respect to the locations of the n pieces. (Neglecting, still,
transmission overhead and decryption time.) I'm not sure what the
lower bound actually is, but it can be increased simply by adding more
pieces to the puzzle.
A single station could serve up multiple pieces. It would only
reveal the k piece if the querying agent can prove that he has the
k-1 piece. Of course if the total number of stations is small then
the "physically move the pieces" trick might work.
"To strive, to seek, to find and not to yield."
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