### Faster Homomorphic Linear Transformations in HElib

Shai Halevi and Victor Shoup

##### Abstract

HElib is a software library that implements homomorphic encryption (HE), with a focus on effective use of "packed" ciphertexts. An important operation (which is used in bootstrapping, as well as in other applications) is applying a known linear map to a vector of encrypted data. In this paper, we describe several algorithmic improvements that significantly speed up this operation: in our experiments, our new algorithms were 30-75 times faster than those currently implemented in HElib for typical parameters. Our techniques also reduce the size of the large public evaluation key, often using 33%-50% less space than the previous HElib implementation. We also implemented a new tradeoff that enables a drastic reduction in size, maybe a 25x factor or more for some parameters, paying only a 2-4x factor in runtime (and giving up some parallelization opportunities).

Available format(s)
Category
Public-key cryptography
Publication info
Keywords
Homomorphic encryptionImplementationLinear transformationsbootstrapping
Contact author(s)
shaih @ alum mit edu
History
2019-05-11: revised
See all versions
Short URL
https://ia.cr/2018/244

CC BY

BibTeX

@misc{cryptoeprint:2018/244,
author = {Shai Halevi and Victor Shoup},
title = {Faster Homomorphic Linear Transformations in HElib},
howpublished = {Cryptology ePrint Archive, Paper 2018/244},
year = {2018},
note = {\url{https://eprint.iacr.org/2018/244}},
url = {https://eprint.iacr.org/2018/244}
}

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