Abstract. Protocols proven secure within the universal composability (UC) framework satisfy strong and desirable security properties. Unfortunately, it is known that within the "plain" model, secure computation of general functionalities without an honest majority is impossible. This has prompted researchers to propose various "setup assumptions" with which to augment the bare UC framework in order to bypass this severe negative result. Existing setup assumptions seem to inherently require some trusted party (or parties) to initialize the setup in the real world. We propose a new setup assumption -more along the lines of a physical assumption regarding the existence of tamper-proof hardware -which also suffices to circumvent the impossibility result mentioned above. We suggest this assumption as potentially leading to an approach that might alleviate the need for trusted parties, and compare our assumption to those proposed previously. For many years, researchers considered the security of protocols in a stand-alone setting where a single protocol execution was considered in isolation. Unfortunately, a proof of stand-alone security for a protocol does not, in general, provide any guarantees when the protocol is executed multiple times in a concurrent fashion (possibly by different sets of parties), or in a network where other protocol executions are taking place. This realization has motivated a significant amount of work aimed at providing models and security definitions that explicitly address such concerns. The universal composability (UC) framework, introduced by Canetti [6], gives strong security guarantees in exactly such a setting. (Other frameworks with similar guarantees also exist [20] , but we adopt the UC model in this work.) We refer the reader to Canetti's paper for a full discussion of the advantages of working within this framework, and focus instead on the question of feasibility. Canetti's initial work already demonstrates broad feasibility results for realizing any (polynomial-time computable) multi-party functionality in the presence of a
Hardware tokens have also been proposed as a physical assumption on which to base secure computation REF .
Universally composable multi-party computation using tamper-proof hardware
In EUROCRYPT, Lecture Notes in Computer Science
Computer Science