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First Bank Transfer via Quantum Cryptography
An anonymous reader writes with today's announcement that "the Austrian project for Quantum Cryptography made the world's first Bank Transfer via Quantum Cryptography Based on Entangled Photons; see also Einstein-Podolski-Rosen Paradoxon." (For more background, see the recent Slashdot post "Quantum Cryptography Leaving the Lab.")
because you wouldn't know which photons contain the data. as soon as you touch it, the other end knows it's datastream has been tampered with.
This is a good overview.
I post links to stuff here
Yes and no. (Well, we *are* talking quantum stuff here, aren't we?) Do a google for "bell inequality" and see if you can get anything from the results. Basically, the answer is , yes, it is instantaneous. And no, it doesn't violate the speed-of-light limitation because you cannot get any useful information transmitted that way. You see, there are two photons which are interlocked. The first photn came at the speed of light and it contains the information you are looking for. The second photon, which serves to validate the quantum key is redundant from the information point of view, it doesn't carry the bank account balance, it only serves to detect tampering in the system.
In order to "read" the photon, you will need to measure the polarization of that photon. But, due to quantum mechanics, as soon as you measure the polarization (for example, with a filter), you will in effect have changed its polarization, and thus its original, actual polarization will be unknown to you. And that's the trick. In essence, the message is "read once." Even if you happen to use the exact same filter as the sender, and read the original photon (and message) for yourself, you can not retransmit the photon with its original, actual polarization -- and thus your "clean one" will arrive at the destination as garbage (thus notifying the receiver that the message has been compromised).
For more info read this primer.
Have you actually tried it?
When I first read about the double slit experiment, I said to myself, "That can't be!"
I cut two slits into a piece of cardboard and directed a flashlight beam through the slits at a wall.
And I observed exactly what one would expect, two diffuse bright spots. I said, "Hmph."
Of course, when I learned a little more, it was obvious why this didn't work. In order to see the interference pattern, your light must be coherent and columnated (as from a laser), and your slits must be very close together, and narrow (with dimensions similar to the wavelength of light). You pretty much need to use a laser as your light source, and rather than a "board" with slits, a sheet of metal with two very thin slits cut into it, very close together.
Something I found very fascinating is that the diffraction pattern you get is the fourier transform of the pattern of slits the system of interference exactly implements the fourier transform integral!
Yes, Quantum Cryptographic Communications (QCC) can help with the requirement that the one-time pad must be transmitted in private. However the one-time pad cannot be reused so your key must be the same size as your text. Thus far, Quantum Cryptographic Communications is not a speedy high bandwidth form of communication. It might be OK to transmit a small key but to date it is not OK for sending, in a reasonable period of time, huge one-time pad keys that are as big as your original message.
Another thing people sometimes gloss over about Vernam one-time pads is that your cipher is only as good as your random number generator! If you generate your one-time pad using the v7 libc rand(3) function your one-time pad is next to useless.
Another important aspect of Quantum Cryptography (Quantum Cryptography is not simply limited to communications) is random number generation. Quantum Cryptographic Random Number Generation (QCRNG) is a useful tool in generating keys (one-time pads, block cypher keys, public/private key pairs, etc.).
The importance of QCRNG goes beyond Vernam one-time pads. You want a cryptographically strong RNG such as a QCRNG when you generate your session keys. Sending predictable keys over a QCC protected link is next to useless!
Now IF you have:
then you will begin to approach the ''unbreakable cypher level'' that some people think you get with Vernam One-Time Pad Ciphers.
chongo (was here)