Text and email messages can be read, regardless of advances in encryption. The world woke up to this fact when Edward Snowden revealed the extent to which intelligence agencies were snooping on private conversations.
Normally only the two respective ends of a conversation have the key to decode it. But if someone steals that key, the participants have no idea that someone is listening to them. Since Snowden’s revelations, innovations such as end-to-end encryption have tried to keep messages secret.
This week, China launched its first quantum satellite. This carries quantum key distribution technology, which uses pairs of photons — light particles wrapped into each other — to send information between two people. If someone tries to eavesdrop on that conversation, the photons react by popping. There’s no decoding, no finding out the secret passphrase.
If the test works, secure communication might be one step ahead of hackers for a brief spell of time.