Quantum Cryptography

[damienpaul]

In a recent Monsters and Critics article (http://science.monstersandcritics.com/news/article_1132147.php/Photon_physics_used_to_foil_hackers), it is claimed:


Photon physics used to foil hackers
Feb 23, 2006, 2:06 GMT

TORONTO, ON, Canada (UPI) -- A University of Toronto scientist says he is using photon physics to prevent hackers from obtaining sensitive government and business data.

How?

A wonderful explanation can be found, via Wikipedia (http://en.wikipedia.org/wiki/Quantum_cryptography) (click on link for full article):

An exerpt:
Quantum cryptography is an approach to securing communications based on certain phenomena of quantum physics.

Essentially, rather than using mathematical techniques to encrypt data - which can invariably be worked out, quantum cryptography focuses on "the physics of information" - such as the photons of light passing along a fibre optic wire etc.

Here is A Bibliography of Quantum Cryptography (http://www.cs.mcgill.ca/~crepeau/CRYPTO/Biblio-QC.html) with some downloadable papers.

If folks have some more info about this technology, please post it

[Duane]

That is--really beyond my comprehension! :eh:

[The Supreme Canuck]

Actually, the principle is pretty simple.

Say Alice wants to send Bob an encrypted message. First, they need to agree on an encryption/decryption key. So Alice sends him a bunch of polarized photons. If polarized one way, the photon represents a 1. If polarized another way, the photon represents a 0. Now, Bob doesn't know which polarization represents a 1 and which a 0 (note that each orientation could mean either, depending on the specific photon). So he guesses for each photon he receives, and sends the guess back to Alice. They use the ones he gets right as the key.

Now, this is secure for two reasons:

First, it is physically impossible to decrypt a message without the key. If you have no key, you have no idea what each photon represents: the polarization could mean either a 1 or a 0. There is no consistency.

Second, if the key is intercepted, Bob and Alice will know. The interception will muck up the polarization due to the way that polarized particles are detected: the detectors are polarized and any particle that is polarized in a different way will have its polarization changed. So when Bob gets the intercepted photons and sends his guess, he will guess correctly less than ~50% of the time (which, statistically, is the percent of the guesses that should be correct). So, seeing this, Alice will keep transmitting new keys until one gets through unmolested, and the message will be encrypted using that key.

Hope that helps.

[damienpaul]

That does help, actually. Thank you for that explanation.

It seems that an inherent strength of this form of security is that mathematics based cryptography can be cracked, but the laws of physics (polarisation etc) can not be "cracked".

(Please correct me if I am wrong)

Also, are there organisations or companies taht utilise this technology?