Hi all,
today Vilasini will talk about composable security in relativistic quantum cryptography, at the usual time and place (see subject line). This is joint work with Christopher and Lídia, and is part of her master thesis. It's also a rehearsal talk for a conference in Oxford next week, so all feedback is welcome!
Abstract:
Cryptographic resources should remain secure even when used as a subroutine within arbitrary protocols: they should be composably secure. It is this notion of security that allows us to construct cryptographic resources and protocols from each other (e.g. a quantum key distribution protocol uses an authenticated classical channel and an insecure quantum channel to construct a shared, secret key resource between two parties). While composable security has been widely studied in non-relativistic cryptography, a general framework for modelling composable security of classical, quantum and relativistic protocols against classical, quantum and non-signalling adversaries is lacking. Here we propose a general framework to this effect and use it to prove novel possibility and impossibility results in relativistic quantum cryptography. In particular, we show that even in a relativistic setting, composable bit commitment is impossible without additional assumptions, and that both bit commitment and coin flipping can be constructed from the primitive channel with delay. Our approach applies the formalism of abstract cryptography to causal boxes.
Best,
-joe