Paper 2020/015

Efficient Homomorphic Conversion Between (Ring) LWE Ciphertexts

Hao Chen, Wei Dai, Miran Kim, and Yongsoo Song


In the past few years, significant progresses on homomorphic encryption (HE) have been made toward both theory and practice. The most promising HE schemes are based on the hardness of the Learning With Errors (LWE) problem or its ring variant (RLWE). In this work, we present new conversion algorithms which switch between different (R)LWE-based HE schemes to take advantages of them. Specifically, we present and combine three ideas to improve the key-switching procedure between LWE ciphertexts, transformation from LWE to RLWE, as well as packing of multiple LWE ciphertexts in a single RLWE encryption. Finally, we demonstrate an application of building a secure channel between a client and a cloud server with lightweight encryption, low communication cost, and capability of homomorphic computation.

Available format(s)
Public-key cryptography
Publication info
Published elsewhere. Applied Cryptography and Network Security 2021 (ACNS 2021)
Homomorphic encryptionLearning with ErrorsKey switching
Contact author(s)
yssong618 @ gmail com
2020-12-04: last of 3 revisions
2020-01-07: received
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Creative Commons Attribution


      author = {Hao Chen and Wei Dai and Miran Kim and Yongsoo Song},
      title = {Efficient Homomorphic Conversion Between (Ring) LWE Ciphertexts},
      howpublished = {Cryptology ePrint Archive, Paper 2020/015},
      year = {2020},
      note = {\url{}},
      url = {}
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