Quantum Cryptography In Action 238
Whitney Wyatt writes: "Discover magazine outlines the first successful laser photon communication utilizing Quantum Cryptography. Called 'Perfect Encryption,' quantum encryption sends the key with the message, however it is impossible for an eavesdropper to intercept the message without changing it. One can only wonder what the FBI will do."
hmmm.. (Score:2, Insightful)
Or is this so complicated that only states and not criminal indivduals can use it?
Martin
Re:Duhh... (Score:0, Insightful)
Perfect encryption already exists... (Score:3, Insightful)
It's called a one-time pad.
So, before everybody and their brother starts talking about how the NSA can already break this, remember that you can, quite easily, build a 'uncrackable' cypher.
And it'll never be breakable, provided you take some sort of security measures. But if you're paranoid, you already do most of those.
Sorry, this is just a preemptive strike against 'the government can monitor my thoughts" crowd.
Back to your normal high S/N ratio.
Cool, but the FBI don't have to do anything. (Score:3, Insightful)
Alice and Bob have a length of optical fibre running between them, and are using quantum cryptography. Eve attempts to evesdrop, but is unable to do so without changing the information in the signal (polarisation etc). Eve is foiled. Hurrah!
Now imagine that Alice and Bob are mere mortals and get to use the phone network like the rest of us.
The system they use is a standard fibre & router system, but the actual fibre is encrypted. What is Eve to do?
Answer: She installs a tap on the repeater, because quantum crypto only works over single lengths of fibre.
As if by magic quantum cryptography only becomes useful to people who get to dig holes in the road, such as phone companies, big business and the government. We little people don't even get to play the game.
Re:Only a matter of time.. (Score:1, Insightful)
Here's a pence, buy a clue
Re:Only a matter of time.. (Score:2, Insightful)
Martin
Osama? (Score:2, Insightful)
Re:Initial handshake? (Score:2, Insightful)
After reading one of the more detailed articles linked to the original, I think one solution is to agree as a matter of protocol that the receiver's report will consist of photons all polarized in a specific direction.
The sender sends some random data to the receiver using photon polarization. The receiver randomly chooses polarizations and reports back to the sender its list of choices without polarizing (or using a consistent polarization). The sender then tells it which choices were correct (once again without polarization). At this point all subsequent data could be sent polarized using the bit pattern from the correctly chosen photons to determine the polarization pattern.
Lessons from history.... (Score:3, Insightful)
I strongly feel that The Codebreakers should be required reading for cryptography advocates. Over and over again the weakest link in any cryptographic system, including the one-time pad has been user error. According to Kahn the NSA successfully decrypted Soviet messages encrypted with "one-time" pads that had been reused due to supply difficulties or clerical errors. They were able to accomplish this by collecting thousands of encrypted dispatches, using traffic analysis, and looking for identical cipher text that might indicate common words, names, or phrases.
Kahn credits cryptographic incompetence to a wide variety of historical disasters from the defeat of the Imperial Russian army during World War I because key officers refused to use codes, to the World War II defeat of enigma because the German Navy had their U-boats transmitting trivial messages to headquarters on a daily basis. (In fact, traffic analysis and radio direction finding efforts were probably more critical than the actual capture of an enigma machine.)
The bottom line is that creating cryptographic systems that mathematically cannot be broken using current technology and probably with any future technology is relatively trivial. Creating socio-technical systems that are resistant to cryptographic incompetence is almost impossible. Most of the focus on algorithms is missing the point when there exist a dozen algorithms that are unbreakable, but no algorithms that are not vulnerable to social engineering attacks, traffic analysis, and dictionary attacks.
I feel that this is really the primary focus of government attacks on cryptographic products, the goal is not to attack the algorithms, but to hinder the development of socio-technical systems that use cryptography effectively. Why worry about if Microsoft Office includes strong, probably unbreakable encryption algorithms, if the software uses password XOR by default for compatibility with earlier versions, the strong cryptography is incompatible with export versions, and a dictionary attack will get 50 percent of the information you want? I am less interested in whether they can create yet another unbreakable encryption system, than creating a security system that allows me to send private e-mail to co-workers who don't understand why they should get a pgp plug-in or how to use it.
no brute force attack (Score:2, Insightful)
The problem is: when you try one the possibilities, how do you know if it's my original plaintext or not? Was my original message "BREAD"? Was it "HELLO"? Was it "DEATH"? The answer is all of the above and none of the above. You can calculate all 2^40 possibilities, and all of them could be correct. You could use a little human intuition -- you could say "DEATH" is more probable than "999.." -- but that only goes so far. You have no reason to believe that "HELLO" is a more or less probably message than "DEATH". If you did have any of that intution, then the actual ciphertext was be literally meaningless to you (aside from its length, of course). You have *NO* way of knowing which is the actual message.
Unless you have the key. This is where quantum cryptography comes into play. Exchanging keys for Vernam ciphers is not hard, but it is impossible (literally) to do electronically and securely. If you send the key over insecured channels, then your key is insecure. If you send your key over encrypted channels, then your key is only as secure as the channel you used, which is to say not secure at all (relatively speaking, seeing as all ciphers are prone to brute-force attack, except for the Vernam cipher). By using quanta, you can tell if your key has been listened to with 1 - (0.5)^n probability, where n is the length of the key.
It always amazes me that people are still willing to spout of crap like "the Vernam cipher is crackable" or "it's prone to brute-force attacks", I guess because they've grown up with the "anything's possible, even the impossible" Hollywood drivel. The Vernam cipher, if the key is generated with a true random number generator (which does not exist, I should say, but it might some day) is uncrackable. It is mathematically provable. Each bit in the ciphertext (again, if the key is completely random) does not depend on any of the bits before or after it. So, suppose you intercept a bit of ciphertext. It is a 0. Was the original plaintext a 0 or a 1? There is a 50% chance it was a 0 and a 50% it was a 1. Tell me how you would crack this; the entire cryptoanalysis field is awaiting your answer. There is no reason a 0 a better answer than a 1; there is no reason a 1 is a better answer than a 0; there is a 0.5 probability it was a 0; there is a 0.5 probability it was a 1. Tell me: was it a 0 or a 1? Take all the computer time you need.
Re:key, not message (Score:3, Insightful)
Check out Generalized Privacy Amplification (1992) by Charles Bennet et. al if you're really interested.