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Alice and Bob meet for lunch. During their meeting, they get their cell phones out and discreetly snap them together and (in what appears to be a senseless act) shake them vigorously.
Tiny accelorometers in each phone independently sample the movement, run the results through an A/D converter,
remove the noise, and use the results to seed a random number generator, which writes a whole bunch of random numbers to memory cards on each phone (how much data is written depends on the sampling rate). The only communication between the phones is an occasional checksum on chunks of the newly generated random data to make sure that they are both generating the same string of numbers. The data chunks are re-generated if disparities (due to errors in A/D conversion, etc) are found.
The phones are then separated. They now each contain the same very long encryption key. They use this shared key to make unbreakably encrypted calls to each other. (Unbreakable because they key is completely random and as long as the message. This is called a one-time-pad and is the only known encryption method known to be 100% secure as long as the key remains secret).
The phones destroy the data on the memory cards that hold the very long encryption key as the data is used. When the data is exhausted, it's time for another meeting...
(And Oscar is out of luck even if he has recorded phone calls and manages to capture the phones after the calls are made).
One Time Pad
http://en.wikipedia.org/wiki/One-time_pad
[cowtamer, Jul 21 2007]
Alice, Bob, and Oscar
http://en.wikipedia.../wiki/Alice_and_Bob
[normzone, Jul 21 2007]
ECHELON
http://en.wikipedia.org/wiki/ECHELON
[nuclear hobo, Jul 22 2007]
NewScientist article
http://technology.n...com/article/dn12912
Synchronised shaking connects gadgets securely [xaviergisz, Nov 16 2007]
Cryptonomicon exerpt
http://books.google...3M9TZRFIgwsnUV5klMk
Mrs. Tenney, the vicar's wife, has become sloppy, and forgotten to close her eyes when she takes the balls out of the bingo machine. [5th Earth, Nov 17 2007]
For //crypto freaks//
http://www.random.org
[Klaatu, Nov 17 2007]
[link]
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Obviously some crypto fans here on the 'bakery. You've made it to five positive votes, no autoboner, and no visible annos. |
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You're not going to get both phones to generate the same random number sequence. For a start, the two sets of accelerometers are going to see slightly different shaking, then, because they're not identical, they're going to send slightly different signals to the processor... Could the phones be plugged together, and both share all of the accelerometer data instead? |
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David, you've got a point about the phones not getting the same cipher stream. This is especially the case if the accelorometers are not right next to each other. But if you know their relative location to each other, and if you know how accurate and precise they are, you can do some filtering and rounding off and make sure that you end up with the same data. The data should be used to seed a random number generator every milisecond or so--not used directly, as Lt_Frank remarked. |
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In an ideal embodiment, the memory card device would be sealed inside the phone, bundled with the accelarometer, and be a write-never-read-once type of device. |
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Best part of this is it would piss off the NSA to no end. Project ECHELON would be rendered even more aburd than it already is. |
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In the end the U.S. government would no doubt ban this technology and reserve it for its own use. |
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I bet this would be endorsed by the NSA. A false sense of security is their stock-in-trade. |
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Your "filtering and rounding off" will destroy the security of the system, at least from a mathematical standpoint. Once you start taking measures like that, you ruin any chance of generating genuinely random numbers, because the "smoothing algorithm", coupled with the fact that the shaking will probably take place at a fairly regular frequency given the tendencies of human action, will itself influence the nature of the numbers generated in a theoretically predictable way. Additionally, you mention removing the noise from the A/D convertors--you should want to keep the noise, because that's one more degree of randomness in the system. |
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A far, far better solution is just to use ONE accelerometer, and then sync the data between phones using built-in physical connection ports. |
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Note link to Cryptonomicon, about a case of near-randomness not being good enough. Okay, it's fictional, but crypto freaks take their random numbers very seriously. |
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