- quantum cryptography relies on individual photons to carry quantum information. But even the best optical fibers can carry these photons only so far—around 200 kilometers—before light absorption makes the process impossible
- Chinese satellite launched in in 2016. The Micius satellite, has set up the first intercontinental quantum cryptography service
- Researchers have tested the system by setting up a secure videoconference between Europe and China
Quantum cryptography relies on what’s called a one-time pad to guarantee privacy – a set of random numbers—a key—that can be used by two parties to encode and decode a message.
- problem with one-time pads is in ensuring that only the transmitter and the receiver have them – ensuring no eavesdropper has copied the key when it is distributed
problem solved by sending the key using quantum particles such as photons, since it is always possible to tell whether a quantum particle has been previously observed – which is the heart of quantum cryptography.
- Once the parties have the assured uncopied key, traditional communication paths can be used.
Micius satellite simply distributes this key from orbit and as it is in a sun-synchronous orbit
- As earth rotates, the satellite transmits the one-time pad to the ground (I am guessing the one-time pad is changed each day?)
There are still weaknesses in the system to continue work on
- Is the satellite considered secure?