Quantum Lunch: Device-independent two-party cryptography secure against sequential attacks.

Speaker: Jed Kaniewski, QMath.

Abstract: Two-party cryptography considers situations in which two parties (Alice and Bob) want to cooperate but since they do not fully trust each other they also try to preserve privacy. For example Alice wants to retrieve a record from a database owned by Bob in a way which does not allow Bob to deduce which record Alice chose but nevertheless does not allow Alice to access the entire database. Unfortunately, such tasks cannot be implemented in a secure way (classically or quantumly). However, security becomes possible, for instance, when the memory of the adversary is limited, which in the quantum world is a reasonable and realistic assumption. We show that such tasks can be executed in a secure manner even in the device-independent setting (i.e. Alice and Bob do not trust the quantum devices they are using). The proof relies on a couple of new trade-offs that connect nonlocality, (anti)commutation and entropic uncertainty, which might be of independent interest for other problems in device-independent cryptography or self-testing.

Joint work with Stephanie Wehner, available at https://arxiv.org/abs/1601.06752