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Quantum Mechanics And Cryptography: A Truly Unbreakable Cipher

Games : Codes And Ciphers

One of the interesting elements about quantum theory is that its whackiness and counter intuitive results coupled with the way that it works in explaining so many phenomena means that we can reliably apply quantum theory to practice.

One thought avenue suggests that an unbreakable cipher could be created as a result due to uncertainty.

If you were to send a pulse of a few photons down a line and decide on their initial direction of vibration, for instance, then you as the sender can effectively send a series of numbers like 10001011.

What is particularly interesting is that the receiver can only deduce which each photon is through applying a polarising filter, but to get the correct result for each photon they need to apply the correct filter. Crucially, if you apply the wrong filter then you will never know for sure the spin of the photon and therefore must discard that result.

Thus, sender A then contacts B after sending the message - as publically as they like - and tell you which filter you should have used for each number. You then tell A which ones you got right and then discard the rest. The resultant number is the key that both parties share for encryption but crucially at no point have they shared that key with each other.

Now the interesting point is this: if someone tried to break into the communication and also applied a filter to each photon and then even listened to your conversation after they still could not work out the key. Why?

Because unless they applied the right filter for every single photon they would have no way of knowing what the end result was. Apply the wrong filter to a particular photon and you have no way of knowing if it was a 1 or a 0. Therefore listening to the communication is futile.

Even better, if anyone actually listened in their observations under quantum theory would change the results at the other end and through doing some basic error checking you can see if your line is secure or not (unsecure or ineffective if there are errors) and the process is repeated.


By: Fred

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