An international team of scientists has proven, for the first time, the security of so-called device-independent quantum cryptography in a regime that is attainable with state-of-the-art quantum technology, thus paving the way to practical realization of such schemes in which users don't have to worry whether their devices can be trusted or not.

In quantum cryptography, the laws of quantum mechanics are exploited to send messages with higher security than is possible in conventional cryptographic schemes based on classical physical phenomena. In principle, quantum communication enables absolute security—that is, no adversary can intercept messages or tinker with them. But in practice, such unconditional security is not currently possible. One main route for unauthorized access is advance manipulation of the communication devices that will be used later. Writing in *Nature Communications*, Rotem Arnon-Friedman and colleagues describe quantum-cryptographic protocols that ensure nearly optimal security, even if the devices are manipulated, and that such device-independent quantum cryptography should be possible with current quantum technology.

Device-independent quantum cryptography is the gold standard of quantum communication, as the advantages of quantum cryptography over its classical counterpart can be realized without having to worry whether the device can be trusted or not. This is an appealing prospect, but so far, device-independent quantum cryptography has been theoretical, with experimental requirements that are not achievable under realistic conditions.

Arnon-Friedman, a Ph.D. student in the group of Prof. Renato Renner in the Institute of Theoretical Physics at ETH Zurich, and co-workers in the U.S., France and the Czech Republic, developed a new theoretical concept called entropy accumulation, and applied it to quantum cryptography. They find that any attack strategy, no matter how complex, can be decomposed into a sequence of simple steps. This is helpful for security proofs, which are notoriously difficult, because every possible attack strategy has to be taken into account. With their new approach, Arnon-Friedman and her colleagues have proven, for the first time, the security of device-independent quantum cryptography in a regime that is attainable with state-of-the-art quantum technology, thus paving the way to practical realization of such schemes.

**Explore further:**
How future quantum computers will threaten today's encrypted data

**More information:**
Rotem Arnon-Friedman et al, Practical device-independent quantum cryptography via entropy accumulation, *Nature Communications* (2018). DOI: 10.1038/s41467-017-02307-4

## antialias_physorg

The way I understand quantum communications it does not guarantee that messages cannot be intercepted. It only guarantees that you will notice shortly after someone starts intercepting (and can then break connection or whatever). It also guarantees safe key distribution (so 'tinkering' really is out).

## rrwillsj

## antialias_physorg

The proof is in the math. That's why these device-independent proofs are so interesting.

Think of it like Heisenberg Uncertainty - it doesn't rely on how tricky you think you can measure something. There's just now way around the math of it.

## Ojorf

Someone listening in on a secure communication has to "measure" the signal. In a quantum system it is impossible to make a measurement without disturbing the system.

Quantum communication algorithms can be devised that are able to detect these disturbances using uniquely quantum properties like entanglement and quantum superpositions.

Communication is immediately terminated when a disturbance is detected.

More: https://en.wikipe...tography

## antialias_physorg

...which is probably the only point where this could be 'hacked'. If the listener can prevent the receiver from telling the sender to stop sending (e.g. by flooding the back-channel) then he can listen in until the message stops (which can be mitigated by requiring periodical acknowledgement of message chunks)

The receiver will know that the message has been intercepted but the listener will still have the message content.

Now, this is just a small niggle because what you exchange with quantum communication doesn't have to be a meaningful message per se. Usually you exchange a key with which to encrypt/decrypt further (classically sent) messages. E.g. if you exchange a key in the way of a one-time-pad and the receiver of the key has ascertained that no one was listening then he can send a classically encrypted message over a normal (non-quantum) channel that is impossible to decrypt.

## rrwillsj

You came this close to assuaging my fears. And then? Off the top of your heads. Without any major effort, began to speculate methods of hacking quantum communications.

Thanks fellas. Thanks a whole damn lot!

## Ojorf

## TheGhostofOtto1923

More cheap shots at legitimate scientists by a professed ignoramus.