New York Times story

[David Howe]

Just received. I pass it on for what its worth but have not as yet been
able to access the story on the web.
>The Key Vanishes: Scientist Outlines Unbreakable Code
>
>By GINA KOLATA
>
>computer science professor at Harvard says he has found a way to
>send coded messages that cannot be deciphered, even by an
>all-powerful adversary with unlimited computing power. And, he says,
>he can prove it.
>
>http://www.nytimes.com/2001/02/20/science/20CODE.html
>
>
>
>For archives see: http://www.interesting-people.org/

It's an interesting (but not entirely secure) variant on One Time Pad.
Basically, you have a single data source (he specifies a orbital satelite)
outputting a true-random stream, presumably intermixed with some sort of
timing / interlock counter
Both users somehow agree (method not discussed) an exact marker to begin
intercepting that stream; they sample a slice from the stream to give them
their symmetric key, and store it.
Symmetric OTP encryption is used to encrypt the message, which is then
transferred, and decrypted with the stored stream (which is then discarded)
Security relies on a high (but reliable) data rate from a true-random data
source forming too big a mass of data to be usefully stored (I think it
envisions intervals between sync-acceptance, intercept of keydata, and
actual sending of data measured in hours, with *very* large amounts of
non-compressable data being transmitted in that time period, so as to
conceal the actual key used in a pool that, if not physically beyond
storage, would take too long to process and extract a message from the key
material and encrypted data.

I doubt it would be practical - the data source would almost certainly be
possible to replace with a pseudo-random stream, thus reducing it to a much
simpler problem (there is no way I can think of to secure the receivers from
a closer, stronger signal overriding the orbital stream; I am sure you can
envision a suitable transmission device that could hit a city-sized
footprint with your own datastream if you needed to; two of them would allow
the message to get though regardless of the deception; one would allow the
message to be decrypted by the black hats, even though the recipient failed
to correctly do so (and that would probably be written off as corruption in
transmission of either data stream or message); this is not to mention the
value of an agent managing to switch the true-random generator "core" to one
that can be switched amongst a choice of prngs... or replace the satellite
with such a "gimmicked" one if usage the system took off.