China has successfully tested its "unhackable" Micius satellite in what it claims is "the world's most secure video conference".
Using quantum cryptography to connect scientists in Europe and China, the satellite's latest feat marks a milestone that is officially named Quantum Experiments at Space Scale (QESS).
Quantum cryptography uses a technique called quantum key distribution (QKD), which encrypts data sent between two parties using quantum particles such as photons, a method that always make it possible to tell if the data has been observed.
It was only last year the satellite was making headlines for transmitting the first "unbreakable" quantum code to the Earth's surface. Now, the technology was used to hold a video conference in September last year that lasted 75 minutes.
In its latest experiment, the Micius satellite sent the quantum key from orbit to a ground station twice, over two locations. The first was a station at Xinglong in China's Hebei province, then - once the Earth had rotated - it did it again at a station in Graz in Austria, by sending a set of random numbers called a one-time pad, encoded in photons.
Next, the scientists used ground-based quantum communication across optical fibres to get the key from these ground stations to their destinations in Beijing's Chinese Academy of Sciences in and Vienna's Austrian Academy of Sciences, respectively.
The video conference was therefore secured by the Advanced Encryption Standard (AES), refreshed every second by 128-bit seed codes.
"We have demonstrated intercontinental quantum communication among multiple locations on Earth with a maximal separation of 7600 km," the researchers behind Micius said.
However, the researchers added that the milestone only constitutes a simple prototype for a global quantum communications network.
"To increase the time and area coverage for a more efficient QKD network, we plan to launch higher-orbit satellites and implement day-time operation using telecommunication wavelength photons and tighter spatial and spectral filtering," they said.
The technology it has turned to is quantum cryptography, a radical break from the traditional encryption methods around. The Chinese project in the city of Jinan has been touted as a milestone by state media.
The pioneering project is also part of a bigger story: China is taking the lead in a technology in which the West has long been hesitant to invest.
In the Jinan network, some 200 users from the military, government, finance and electricity sectors will be able to send messages safe in the knowledge that only they are reading them.
China's push in quantum communication means the country is taking huge strides developing applications that might make the increasingly vulnerable internet more secure. Applications that other countries soon might find themselves buying from China.
So, what is this technology into which the country is pouring massive resources?
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