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Multi-Key Homomorphic Encryption from TFHE

  • Hao Chen
  • Ilaria Chillotti
  • Yongsoo SongEmail author
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 11922)

Abstract

In this paper, we propose a Multi-Key Homomorphic Encryption (MKHE) scheme by generalizing the low-latency homomorphic encryption by Chillotti et al. (ASIACRYPT 2016). Our scheme can evaluate a binary gate on ciphertexts encrypted under different keys followed by a bootstrapping.

The biggest challenge to meeting the goal is to design a multiplication between a bootstrapping key of a single party and a multi-key RLWE ciphertext. We propose two different algorithms for this hybrid product. Our first method improves the ciphertext extension by Mukherjee and Wichs (EUROCRYPT 2016) to provide better performance. The other one is a whole new approach which has advantages in storage, complexity, and noise growth.

Compared to previous work, our construction is more efficient in terms of both asymptotic and concrete complexity. The length of ciphertexts and the computational costs of a binary gate grow linearly and quadratically on the number of parties, respectively. We provide experimental results demonstrating the running time of a homomorphic NAND gate with bootstrapping. To the best of our knowledge, this is the first attempt in the literature to implement an MKHE scheme.

Keywords

Multi-Key Homomorphic Encryption Bootstrapping 

Notes

Acknowledgments

The second author (I.C.) has been supported in part by ERC Advanced Grant ERC-2015-AdG-IMPaCT and by the FWO under an Odysseus project GOH9718N. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the ERC or FWO.

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Copyright information

© International Association for Cryptologic Research 2019

Authors and Affiliations

  1. 1.Microsoft ResearchRedmondUSA
  2. 2.imec-COSIC, KU LeuvenLeuvenBelgium

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