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New Quantum Cryptography Speed Record
Roland Piquepaille writes "Physicists from the National Institute of Standards and Technology (NIST) have established a world's speed record for 'unbreakable' encryption with their cryptographic system based on the transmission of single photons. With this kind of method, messages cannot be intercepted without detection, meaning transmission is always safe. The NIST 'quantum key distribution' (QKD) system was used between two buildings located 730 meters apart for transmitting a stream of photons at a rate of 1 million bits per second. While it might not look very fast, its 100 times faster than with previous quantum distribution systems. This overview contains more details and references about information theory."
1,000,000 / 8 = 125,000 /1024 = 122.1
125,000
Not to bad for not using wireless undetectable (so far) encryption.
Your last paragraph is the way that QC is actually used (or so I have read in some random QC article):
(1) Sender generates long random key
(2) Sender transmits key
(3) Receiver receives key
(4) Received acks that the key has been received securely
(4A) Design of a secure "ack" channel is an interesting question, don't know the answer for that off the top of my head!
(5) Sender computes (message XOR key)
(6) Sender transmits (message XOR key)
(7) Receiver receives (message XOR key)
(8) Receives computes ((message XOR key) XOR key) == message
Aaahhh! and it runs Linux. Mod me up.
("We are currently using a Linux operating system with custom drivers for the boards.")
17779 eligible voters in a district, 17779 'vote' as one. This is Russia.
Even if you can detect the evesdropping, by that time, it's too late; the evesdropper already has part of the message. Granted, it's only a single bit, but it might be the most important bit of the message.
No, no, no, no. All you're sending is the key. If the key is compromised, all you have to do is throw that key away and send another key. No actual data from the message is sent. Once the key is received, and you know it hasn't been comprimised, you can send the encrypted data through any unsecure channel you like at any speed. You could cache the keys in advance so the transmission can be unaffected by a DOS attack on the quantum transmission.
The whole point of quantum crypto is that if someone did try to act as a repeater, then they would be detected. This is not because you would "see" them standing there intercepting your data ( although that would be a possibility ), but because the protocol used to transmit the information securely would reveal the fact that the data had been intercepted and then retrasmitted.
The basics are like this. Small particles ( like photons of light ) have a property called spin. You can set the spin of a particle when you transmit it by using the right kind of gear. You can test the spin of the particle in several different ways, but not all spins can be detected correctly by all tests. So if you have no idea what the spins are, you can't know which test to use. So if you use a random sequence of tests, you will sometimes have the right test, and sometimes not. So to transmit information, our protocol works like this ( taken from "The Code Book" by Simon Singh, p.346-7 ):
1) Alice sends Bob a series of photons, and Bob measures them.
2) Alice tells Bob on which occasions he measured them in the correct way. Although Alice is telling Bob when he made the correct measurement, she is not telling him what the correct result should have been, so this conversation can be tapped without any risk to security ).
3) Alice and Bob discard the measurements that Bob made incorrectly, and concentrate on those that he made correctly in order to create an identical pair of onetime pads.
4) Alice and Bob test the integrity of their onetime pads by testing a few of the digits.
5) If the verification procedure is satisfactory, they can use the onetime pad to encrypt a message; if the verification reveals errors, they know that the photons were being tapped by Eve, and they need to start all over again.
It is true that Eve could listen in on the line, intercepting photons sent by Alice and try to recreate the same stream of photons to Bob with the same spins. However, she can only use a test once, she can't copy a photon and test it using several different tests. So she will inevitably use the wrong test on a number of photons, and so not know what the true spin ought to be, and so can't reproduce them. She also can't know what series of tests Bob will use to test the photons he is receiving. So inevitably what would happen is this: Eve uses the wrong test on some photons, doesn't know what their spins ought to be, sends out some with different spins; Bob however uses the correct tests on some of those photons that Eve "made up", but gets different results from Alice ( because some of the spins are different from what Alice originall sent ), so when they compare results it becomes obvious that they don't have the same sequence of results. Furthermore, Eve can't know where the errors are going to come up and how she should fix them, so she couldn't intervene successfully in this verification step to make it seem correct when its not.
Long story short - you can't make a successful repeater ( down side to this is you can't use any network for transmitting the photons, as a network necessarily involves repeaters - aka routers/gateways - you must have a direct line from sender to receiver so the photons don't get altered ).
There are a thousand forms of subversion, but few can equal the convenience and immediacy of a cream pie -Noel Godin