With its Micius satellite, China proved it possible to use individual photons sent from space to communicate in almost total secrecy. Now, other countries are playing catch-up.

Time is running out for our encryption – although no one knows quite when that will be. This threat is posed by quantum computers, which are ideally suited to cracking classical encryption schemes like RSA through sheer brute force. Any data being sent place to place is vulnerable – from military secrets to the financial and medical records of private citizens.

“If you’re interested in the long-term security of data that has been transmitted … you should probably be concerned about the future emergence of quantum computing technology, because of the ‘harvest now, decrypt later’ attack that could be present on any encrypted data,” says Professor Tim Spiller, director of the UK’s Quantum Communications Hub. “That’s the looming threat.” Intelligence agencies are already collecting and storing vast troves of data, ready...