Chinese satellite used quantum cryptography for secure intercontinental video conferencing

Quantum cryptography allows people to make communication completely secure by protecting communication channels from listening. This technology is becoming increasingly important. Physicists have long known that quantum computers (when they appear in a form suitable for work) allow hacking into any types of cryptographic protection. Well, since the emergence of commercial quantum computers is not far off, scientists have to invent more and more sophisticated data protection methods. All this is in the interests of business, government organizations, the military.

In general, quantum cryptography is important for anyone who needs almost one hundred percent protection against hacking. But there is one problem. The fact is that quantum cryptography works with individual photons that carry quantum information. But even the best fiber optic cables can drive photons at a distance of no more than 200 km, before the absorption process makes all these attempts meaningless. Therefore, quantum cryptography previously worked (and then in the test version) only at short distances.

But Chinese scientists have developed a satellite that removed the obstacle in the form of a distance. This satellite, Micius , was launched in 2016. During the previous years he performed various tasks and went to the operational level. Last summer, he earned full power and was able to teleport a photon from orbit directly to Earth.

As you might guess, quantum cryptography is a method of protecting communications, based on the principles of quantum physics. Unlike traditional cryptography, which works with purely mathematical methods to ensure the secrecy of information, quantum cryptography focuses on physics. The process of sending and receiving information is carried out by physical means, as an example - electrons or photons. But eavesdropping can be considered a change in certain parameters of physical objects - in this case, carriers of information.

The technology of quantum cryptography is based on the fundamental uncertainty of the behavior of the quantum system, which is expressed in Heisenberg’s uncertainty principle. In this case, one cannot simultaneously obtain the coordinates and momentum of a particle, and one cannot measure one photon parameter without distorting another.

Ideally, using quantum phenomena, you can create a communication system that allows you to detect eavesdropping in 100% of cases. As mentioned above, eavesdropping on a quantum channel leads to a change in the parameters of the original signal. The noise level in the system will increase, and users of the system will immediately be able to recognize the fact of eavesdropping, as well as measure the level of its activity.



Devices for quantum cryptography can not be called new. Thus, the first functioning quantum-cryptographic system was created in 1989 at the IBM Research Center by scientists Bennett and Brassard. The system was a quantum channel that worked, on the one hand, with Alice’s transmitting apparatus, and on the other, with Bob’s receiving apparatus. Both devices were at a distance of 1 meter from each other. The control took place with the help of a computer that was loaded with software representations of legal users of the attacker Eva, who was trying to "overhear".

Particles in the quantum cryptography system can be called quantum keys. Their distribution is a key process. If both sides have the key, they can communicate through traditional communication channels without the threat of being overheard. So, the Chinese satellite sends the keys from orbit. It is located in orbit in such a way that it passes over certain points on the earth’s surface at about the same time every day.

When the satellite is located at a Chinese ground station in Hebei Province, it sends the key to Earth, which allows you to open secure communication channels. The Chinese managed to open a protected video link between the Chinese Academy of Sciences in Beijing and the Austrian Academy of Sciences in Vienna. Thus, both parties received by key. Video communication was carried out through the traditional channel.

"We have demonstrated the possibility of intercontinental quantum communication, between two points that are 7,600 kilometers apart," the project participants said.

Despite the successes, it is too early to talk about the commercial use of technology. At the moment, this is only proof of the performance of the system, based on the theoretical principles presented earlier.

Ref: arxiv.org/abs/1801.04418