Today, most people assume that the best way to ensure confidentiality and integrity of communications and underlying data is through encryption, which is an ancient 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 immense computing power beyond the realms of today’s classical computers. One of these methods, knows as the “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 those built by IBM or Google, such assumptions will no longer hold.

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

Quantum cryptography, the science of exploiting quantum mechanical properties to perform cryptographic tasks, uses Heisenberg’s Uncertainty Principle and the No-Cloning Theorem. The Uncertainty Principle, formulated in 1927, states there is a fundamental limit to the precision with which a particle’s physical properties can be known; the more precisely we can determine the position of a particle, the less accurately its momentum can be identified, 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 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 inseparable bond, no matter how far located they are from each other. Even if they are situated 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 developing devices that generate such pairs of entangled photons, one of which is to be sent to one user, and the other, to another.

This research uses one of the numerous properties of light, its polarization, to encode information in the photon. Each pair of photons is entangled one with the other after being picked up one by one with a single-photon detector connected to a computer that converts them into electrical signals. We can then ultimately obtain the same randomized string on both screens – that means the same key.

Besides, 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.