アイテム詳細

要旨

Designing communications protocols specifically adapted to relativistic situations (i.e. constrained by special relativity theory) is taking advantage of uniquely relativistic features to accomplish otherwise impossible tasks. Kent [Ken99] has demonstrated, for example, that secure bit commitment is possible using a protocol exploiting relativistic causality constraints, even though it is known to be impossible otherwise. Therefore, Kent's protocol gives a theoretical solution to the problem of finding commitment schemes secure over arbitrarily long time intervals. The functionality only requires from the committer a sequence of communications, including a post-revelation validation, each of which is guaranteed to be independent of its predecessor. We propose to verify the security of the relativistic commitment not as a stand alone protocol, but as an entity which is part of an unpredictable environment. To achieve this task we use the universal composability paradigm defined by Canetti [Can01]. The relevant property of the paradigm is the guarantee of security even when a secure protocol is composed with an arbitrary set of protocols, or, more generally, when the protocol is used as an element of a possibly complex system. Unfortunately, Kent's relativistic bit commitment satisfies universal composability only with certain restrictions on the adversarial model. However, we construct a two-party universal composable commitment protocol, also based on general relativistic assumptions.