Composable security in relativistic quantum cryptography

Relativistic protocols have been proposed to overcome certain impossibility results in classical and cryptography. In such a setting, one takes the location of honest players into account, and the signalling limit given by the speed of light to constraint the abilities of dishonest agents. , composing such protocols with each other to construct new cryptographic resources is to be insecure in some cases. To make general statements about such constructions, a framework for modelling cryptographic security in Minkowski space is required. , we introduce a framework for performing such a modular security analysis of classical and cryptographic schemes in Minkowski space. As an application, we show that (1) fair and coin flipping can be constructed from a simple resource called channel with delay; (2) coin flipping, bit commitment and channel with delay through any classical, quantum or -quantum relativistic protocols are all impossible without further setup assumptions; (3) it is to securely increase the delay of a channel, given several short-delay channels as . Results(1) and (3) imply in particular the non-composability of existing relativistic bit and coin flipping protocols.