Quantum Cryptography

You might have heard about Cryptography, it is a one kind of technique that converts plain text into cipher text. In quantum cryptography cipher text is made by quantum mechanical effect. It’s hard to decipher text, that’s main benefit of quantum cryptography. If you want to transfer some confidential message to another party, you must need Cryptography. If you send this message as it is then anybody can intercept it and reveal your message. That might cause you lot of loss. There are many techniques to convert your plain text into cipher text (changed text). However this classical technique is not fully safe, because it can be broken by some another technique like brutal force (Might take 2-3 years).

Photon Properties:

          To understand quantum cryptography, you must behold photon. It is basic particle of light. It has considerably neglecting mass. It can exist all its possible state at once. That means it spins all direction at once, horizontally, vertically and diagonally. On that state photon is called unpolarized photon. Now this photon is worthless to our objective. We must make it polarized photon. Now how can we do that? There is one polarizing filter that makes photon polarized. If we pass photon from horizontal filter then we get photon with horizontal spin. Now you might be wondering how these photon properties can attach with quantum cryptography???

How to make cipher using quantum cryptography???

          Suppose our message is f-i-r-e and its binary is 11010011010011. Now sender can attach vertical polarized photon as 1 and horizontal polarized photon as 0. Sender can choose randomly polarizing filter and pass its photons through it and record the polarization of each photon. Sender knows which photon polarization receiver should receive.

          Here, sender uses LED (Light Emitting Diode) to generate photons. Sender will pass their photons (original message) through randomly chosen filter either + or X filters. After then photon has one of four possible states: vertical (|), horizontal (--), diagonal (/) or stateless (). When receiver receives message, he/she will decide which filter he/she should use. Receiver cannot use both filter together. Receiver asks every time which filter he/she should use for particular photon. In reply sender tells him answer as a ‘correct’ or ‘incorrect’.

          For example, receiver tells sender that he has used + filter for that particular photon. In reply sender tells him ‘incorrect’. Then receiver will use X filter. Suppose, the third party is listening this conversation then he can know only know about filters, but he cannot determine what actual photon sequence is.

          " Heisenberg's uncertainty principle limits the precision with which the position and momentum of a quantum particle can be determined simultaneously, but can also be exploited for secure information transfer." Quantum cryptography requires shared key to encode and decode message. If anyone tries to intercept communication, it becomes detectable because quantum particle are fragile, interception might change its behavior.     

          This new quantum cryptography is already being used by some government agencies and banks. Here light is used for transmission via optical fiber, so that it is limited by range up to 200 km.    

 Recent News:

          The scientists of LMU (Ludwig-Maximilians-Universitaet) Munich,Germany sent a cipher message from airplane to a ground station through atmosphere on 3 , April, 2013.