Quantum Cryptography

The What

Quantum Cryptography is one the latest advancements in Cryptography. This technique involves using the "quantum mechanics" concept of Physics in Cryptography.

Quantum Mechanics deals with atomic and sub-atomic particles, and endorses the particle nature of light, which carries packets of energy called Photons. This concept was first postulated by Einstein as The Photo-Electric Effect(for which he received the Nobel Prize in 1921), and later proved by Max Planck and others.

The Photo-Electric Effect is the emission of electrons when light (electromagnetic radiation) hits a surface.

This concept is implemented in Cryptography to improve security. The key implementation is in Quantum Key Distribution called in short, as QKD.

The How

QKD is used for sharing secret keys between two parties, by using two bit sequences - Vertical and Horizontal Polarizations, in the form of photons

In cryptography, the sender and receiver are usually called Bob and Alice. Let us assume that Alice sends out a set of photons. Bob then sends these through a beam splitter, which causes the beams to split up in a specific pattern - taking either Vertical or horizontal polarizations. Bob then sends back data regarding the photons sent. Alice compares the received messages with the original photons sent. Photons in the wrong orientation are discarded, and the rest is used as the encryption key.

Picture from the Washington University of Illinois website

This is a very secure way of sharing the encryption key, as the eyedropper does not get to know the key at any point in time, and any distortion done to the data transmitted can be easily identified when the photon orientations do not match, and the channel can be safely discarded by both Alice and Bob. 

It however cannot be used as a stand-alone. This technology has to be integrated with other underlying encryption techniques. 

Who are all working on this?

China, USA, Canada and several European countries have been working on developing QKD, the efforts of IBM being substantial and notable. However, an ambitious China has now emerged as the world leader in Quantum Key Distribution, as it has already tested the technology on a small scale, as against USA, which is still working on it. 

QKD has proved to be safe against intercept and resend, man-in-the-middle-attack, Photon number splitting attack, Denial of Service and Trojan Horse attacks

This technology is mainly aimed for use by governments and defense organizations. It will take several years before the technology reaches the public.