Efficient Composable Oblivious Transfer from CDH in the Global Random Oracle Model

Bernardo David, Rafael Dowsley

Research output: Conference Article in Proceeding or Book/Report chapterArticle in proceedingsResearchpeer-review


Oblivious Transfer (OT) is a fundamental cryptographic protocol that finds a number of applications, in particular, as an essential building block for two-party and multi-party computation. We construct the first universally composable (UC) protocol for oblivious transfer secure against active static adversaries based on the Computational Diffie-Hellman (CDH) assumption. Our protocol is proven secure in the observable Global Random Oracle model. We start by constructing a protocol that realizes an OT functionality with a selective failure issue, but shown to be sufficient to instantiate efficient OT extension protocols. In terms of complexity, this protocol only requires the computation of 6 modular exponentiations and the communication of 5 group elements, five binary strings of security parameter length, and two binary strings of message length. Finally, we lift this weak construction to obtain a protocol that realizes the standard OT functionality (without any selective failures) at an additional cost of computing 9 modular exponentiations and communicating 4 group elements, four binary strings of security parameter length and two binary strings of message length. As an intermediate step before constructing our CDH based protocols, we design generic OT protocols from any OW-CPA secure public-key encryption scheme with certain properties, which could potentially be instantiated from more assumptions other than CDH.
Original languageEnglish
Title of host publication Cryptology and Network Security. CANS 2020.
EditorsStephan Krenn, Haya Schulman, Serge Vaudenay
Publication date2020
ISBN (Print)978-3-030-65410-8
ISBN (Electronic)978-3-030-65411-5
Publication statusPublished - 2020
EventCryptology and Network Security -
Duration: 14 Dec 2020 → …
Conference number: 2020


ConferenceCryptology and Network Security
Period14/12/2020 → …
SeriesLecture Notes in Computer Science


  • Oblivious Transfer
  • Cryptographic Protocol
  • Computational Diffie-Hellman Assumption
  • Universal Composability
  • OT Extension Protocols
  • Static Adversaries
  • Global Random Oracle Model
  • Public-Key Encryption
  • Modular Exponentiations
  • Security Parameter Length


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