Today, most people assume that the best way to ensure confidentiality and integrity of communications, as well as underlying data, is through encryption, which is a very old method to secure communication that appeared 2,500 years ago in Greece during Peloponnese Wars*.

Even the most modern form of encryption is primarily based on the assumption that the mathematical models used to encrypt are too complex to decode without access to an extremely large computing power beyond the realms of today’s classical computers. One of these methods, knows as “asymmetrical method” uses two encryption keys, one public and one private.

*Wikipedia: Scytale – History

Unfortunately, with the advent of massively powerful quantum computers in the next decade, such as the ones built by IBM or Google, such assumptions will no longer hold true.

Much of today’s encryption will become vulnerable as quantum computers may solve complex optimization problems many orders of magnitude faster than a single-core classic computer*. Moreover, encrypted information which has been downloaded today may be decrypted offline in the coming years.

* IDC Technology Spotlight April 2016

Quantum cryptography, the science of exploiting quantum mechanical properties to perform cryptographic tasks, uses Heisenberg’s Uncertainty Principle and the No-Cloning Theorem. According to the Uncertainty Principle, formulated in 1927, there is a fundamental limit to the precision with which physical properties of a particle can be known; the more precisely we can determine the position of a particle, the less precisely its momentum can be known, and vice versa. The No-Cloning Theorem, first articulated by Wootters, Zurek and Dieks in 1982, demonstrates that it is impossible to create a copy of an arbitrary unknown quantum state.

The best example of quantum cryptography that exists today is quantum key distribution (QKD). It offers absolute protection, even against quantum computers, because its strength does not depend on mathematical complexity, as in the case of post-quantum cryptography, but on physical principles.

Current research on quantum encryption is based on the Quantum Entanglement Phenomenon, discovered by Albert Einstein in 1935, and first experimentally proven by the French physicist Alain Aspect in 1981.

Strange as it may seem, two intricate particles (material or light) form an indivisible bond, no matter how far they are located from each other. Even if they are placed at the opposite ends of the galaxy, everything that happens to one instantaneously has an impact on the other. In light of this, several laboratories are currently working on developing devices which generate such pairs of entangled photons, one of which to be sent to one user, and the other, to another one.

This is done with the use of one of numerous properties of light, its polarization, to encode information in the photon. As each pair of photons is entangled, one with the other, after having been picked up one by one with a single-photon detector connected to a computer that converts them into electrical signals, we can ultimately obtain the same randomized string on both screens – that means the same key.

In addition, entanglement offers another invaluable advantage: any attempt by a third party to “read” the photons alters the key in a way that will be evident to participants.

Accordingly, one of the authorized users can then immediately discard that key and request the quantum device to generate a new one. Thus, it will be impossible to defeat.