## Cryptology ePrint Archive: Report 2017/1165

Fast and Universally-Composable Oblivious Transfer and Commitment Scheme with Adaptive Security

Megha Byali and Arpita Patra and Divya Ravi and Pratik Sarkar

Abstract: Adaptive security embodies one of the strongest notions of security that allows an adversary to corrupt parties at any point during protocol execution and gain access to its internal state. Since it models real-life situations such as hacking", efficient adaptively-secure multiparty computation (MPC) protocols are desirable. Such protocols demand primitives such as oblivious transfer (OT) and commitment schemes that are adaptively-secure as building blocks. Efficient realizations of these primitives have been found to be challenging, especially in the no erasure model. We make progress in this direction and provide efficient constructions that are Universally-Composable in the random oracle model.

Commitment Scheme: We present an adaptively secure commitment scheme in the Global Random Oracle model solely relying on observable random oracle (ORO). Our commitment scheme has a one-time offline setup phase, where a common reference string (crs) is generated between the parties using an ORO. In the online phase, the parties use the crs and ORO to generate commitments in a non-interactive fashion. Our construction incurs communication of 4k bit strings and computation of 4 exponentiations and 4 random oracle queries for committing to an arbitrary length message. Empirically, it takes around 0.18ms and 0.2 ms for committing to 128 bits and 2048 bits respectively. It finds applications in secure two-party computation (2PC) protocols that adopt offline-online paradigm, where the crs can be generated in the offline phase and the scheme can be used in the online phase.

Category / Keywords: cryptographic protocols / Oblivious Transfer, Commitment Schemes, Universal Composability, Adaptive Security, Erasures

Date: received 30 Nov 2017, last revised 21 Mar 2018

Contact author: iampratiksarkar at gmail com

Available format(s): PDF | BibTeX Citation

Short URL: ia.cr/2017/1165

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