Welcome to the Twilight Zone of quantum cryptography

Quantum computing, the world of the bizarre and the super-fast, will be a game changer for cryptography. Other areas will benefit from quantum physics speed such as weather forecasting, medicine, search engines, robotics, and big data analytics, but it is in cryptography that we will see early applications of the technology.

The current cryptographic method of RSA public/private key encryption derives it’s security from the difficulty of computing the private (decryption) key from the public (encryption) key. Using the fastest computers available today, it is infeasible to calculate a private key due to the length of time it would take to perform the mathematical calculations. Quantum computing will change all that. If today’s fastest computers are the speed of Usain Bolt, quantum computers will be as fast as the speed of light – simply no comparison.

The concept of quantum physics is surreal and bizarre when viewed from a classical physics (non-quantum) perspective. Quantum physics involves the microscopic level, down to the level of one particle of light – a photon. Strange things happen at this level, which cannot be explained by classical physics. In the Twilight Zone of quantum physics, an object can be in two states at once – a single object can be in two places at exactly the same time, a cat can be both dead and alive at the same time, and there are multiple parallel universes co-existing at all times. Stranger still, these various states co-exist only while not measured or observed. Quantum physics defies common sense and appears more science fiction when viewed from our classical physics perspective, but the quantum scientists assure us that this is how things work at a microscopic level. As bizarre as it sounds, we need to take their word for it.

Computers also operate at a microscopic level so it should be possible to construct a quantum computer that works on quantum principles. A quantum computer will be able to perform multiple tasks at the same time. This is unlike a conventional computer – we are not talking different threads here. Let me explain. Typically a computer programme contains many loops, a sequence of instructions which are performed multiple times. A conventional computer can only perform loops sequentially. A quantum computer could perform loops simultaneously. Each in it’s own universe (!?), due to the fact that at a microscopic level, all states of a particle exist at once as long as no-one is watching.

The difficulty so far, has been in building the hardware to perform quantum physics calculations, and then figuring out how to write the software. Once a quantum computer has been successfully constructed however, all current encryption methods will be instantly redundant. Some cryptographers have been quietly working on methods of quantum cryptography that will be needed to replace existing technologies, to secure data. One such effort uses the polarisation of photons, exploiting the uncertainty surrounding the plane in which an electrical field oscillates.

This week’s Economist magazine has an article describing three quantum-based methods of securing the transmission of an encryption key through local fixed lines. Quantum physics is used to secure the key during transmission, as the quantum event is uncertain, any eavesdropper will not be able to reassemble the message correctly and send it to it’s intended destination.

Another article this week exploits the strange behaviour of quantum particles with a tongue-in-cheek examination of a Quantum Bank in which all deposits go into all accounts making everyone rich! Now there’s an idea worth contemplating.


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