Device-Independent Cryptography
Quantum nonlocality enables cryptographic protocols that are secure even when the systems are not well characterized or manufactured by an untrusted provider.
Quantum properties lead to levels of security for cryptographic tasks that are inconceivable even with the most powerful classical technology. The notorious example is quantum key distribution (QKD), in which two parties, Alice and Bob, establish a secret key unknown to an eavesdropper, Eve, with unlimited resources. This allows them to communicate with unconditional security, in contrast to current cryptosystems that rely on computational assumptions. A successful implementation of QKD requires a precise characterization of the underlying quantum system. Deviations from such assumptions led to the hacking of many commercially available QKD schemes. Hence, without a full characterization of the systems, or if they are manufactured by an untrustworthy provider, can we still achieve secure communication? Surprisingly, quantum properties also offer a solution to this problem, and secure communication can be established even when the users are ignorant about the internal working of their devices. This is the device-independent (DI) paradigm, which models systems and measurement apparatuses as black boxes where the only relevant information is the statistics of inputs (measurement settings) and outputs (measurement outcomes).