Quantum direct communication: secrecy without key distribution


An interesting development in the world of quantum encryption.

In the last couple of years, we’ve seen a number of quantum key distribution systems being set up that boast close-to-perfect security (although they’re not as secure as the marketing might imply).

These systems rely on two-part security. The first is the quantum part which reveals whether a message has been intercepted or not. Obviously this is no use when it comes to sending secret message because it can only uncover eavesdroppers after the fact.

So Alice sends a one time pad over this quantum channel that she and Bob can later use to encrypt and send a message classically. If this key is compromised, Alice sends another.

What guarantees the security is not quantum mechanics but the second part of the system: the one time pad.

Today, Seth Lloyd and colleagues at the Massachusetts Institute of Technology in Cambridge, publish a way of guaranteeing security over a quantum channel without having to fall back on a one time pad.

Their idea is to send a message over a standard quantum channel without bothering with a one time pad. The security, they say, can be monitored by randomly checking the channel to see whether any of the qubits are being lost (potentially to Eve).

The security of the channel then depends on how much loss of information Alice and Bob are willing to accept, but can always be improved by checking more often for eavesdroppers.

Quantum direct communication, as the team call it, looks interesting. But it will be demanding to implement, not least because any noise in the channel will look like an eavesdropper. So it looks as if this idea will have to be limited to short range applications where noise can be kept to a minimum.

Nevertheless, a cool idea.

Ref: arxiv.org/abs/0802.0656: Quantum Direct Communication with Continuous Variables

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