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arXiv:1808.10145 · Entropy

On the Composability of Statistically Secure Random Oblivious Transfer

Rafael Dowsley, Jörn Müller‐Quade, Anderson C. A. Nascimento

Published Jan 16, 2020• 3 citations
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Abstract

We show that random oblivious transfer protocols that are statistically secure according to a definition based on a list of information-theoretical properties are also statistically universally composable. That is, they are simulatable secure with an unlimited adversary, an unlimited simulator, and an unlimited environment machine. Our result implies that several previous oblivious transfer protocols in the literature that were proven secure under weaker, non-composable definitions of security can actually be used in arbitrary statistically secure applications without lowering the security.

DOI
10.3390/e22010107

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We show that random oblivious transfer protocols that are statistically secure according to a definition based on a list of information-theoretical properties are also statistically universally composable. That is, they are simulatable secure with an unlimited adversary, an unlimited simulator, and an unlimited environment machine. Our result implies that several previous oblivious transfer protocols in the literature that were proven secure under weaker, non-composable definitions of security can actually be used in arbitrary statistically secure applications without lowering the security.
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Abstract. We investigate the definition of statistical security (i.e., security against unbounded adversaries) in the framework of reactive simulatability. This framework allows to formulate and analyze multi-party protocols modularly by providing a composition theorem for protocols. However, we show that the notion of statistical security, as defined by Backes, Pfitzmann and Waidner for the reactive simulatability framework, does not allow for secure composition of protocols. This in particular invalidates the proof of the composition theorem. We give evidence that the reason for the non-composability of statistical security is no artifact of the framework itself, but of the particular formulation of statistical security. Therefore, we give a modified notion of statistical security in the reactive simulatability framework. We prove that this notion allows for secure composition of protocols. As to the best of our knowledge, no formal definition of statistical security has been fixed for Canetti’s universal composability framework, we believe that our observations and results can also help to avoid potential pitfalls there.
The study of secure multiparty computation has yielded powerful feasibility results showing that any efficient functionality can be securely computed in the presence of malicious adversaries. Despite this, there are few problems of specific interest for which we have highly efficient protocols that are secure in the presence of malicious adversaries under full simulation based definitions (following the ideal/real model paradigm). Due to the difficulties of constructing such protocols, many researchers have resorted to weaker definitions of security and weaker adversary models. In this paper, we construct highly efficient protocols for the well-studied problem of oblivious polynomial evaluation. Our protocol is secure under standard cryptographic assumptions for the settings of malicious adversaries, and readily transform to protocols that are secure under universal composability and in the presence of covert adversaries. Our protocol is constant round and requires O(d · s) exponentiations, where d is the degree of the polynomial and s is a statistical security parameter (that should equal about 160 in practice).
We introduce a general construction of fully simulatable oblivious transfer based on lossy encryption. Furthermore, we extend the common definition of lossy encryption by introducing the notion of computationally lossy encryption. If the cryptosystem used is computationally lossy, our general construction yields oblivious transfer protocols with computational security for both parties. Otherwise, when regular statistically lossy cryptosystems are employed in this construction, it yields oblivious transfer protocols with statistical security for the sender. The construction introduced in this paper is realizable from rerandomizable, homomorphic and lossy cryptosystems in general. Thus, it yields specific constructions based on different assumptions, such as DDH, LWE and McEliece. Moreover, it proves the equivalence of fully simulatable oblivious transfer and lossy encryption.