BBC Technology

Quantum cryptography has emerged from the laboratory and into the real world.

Using properties of quantum physics, the technique encrypts data with keys that reveal if they have been intercepted or tampered with.

US company Magiq and Swiss firm ID Quantique have already sold hardware to several customers keen to protect data with quantum cryptography.

Governments and armed forces are thought to be among the first users of the technology.

Encryption usually involves scrambling data with long numeric keys that stop other people reading it. Once you can guarantee the key is secret, you can use that for encrypting the data or for any other cryptographic tasks you want to do

The information inside the message is effectively kept secure because of the time it would take an eavesdropper to sort through all possible keys used to scramble the data.

But quantum cryptography scrambles data in a different way by using the strange properties of the quantum world to guarantee that keys have been swapped securely.

Information about the key is encoded onto a single photon.

Quantum physics guarantees that the properties of the photon will change if anyone intercepts it and tries to read the information off it.

Once two parties have swapped a key that they know to be safe they can be sure that the messages they are sending each other are secure.

The current record for long-distance quantum key distribution is 120km.