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Paper 2021/1085

Homomorphic Encryption for Multiple Users with Less Communications

Jeongeun Park

Abstract

Keeping privacy for every entity in outsourced computation is always a crucial issue. For efficient secure computation, homomorphic encryption (HE) can be one of nice solutions. Especially, multikey homomorphic encryption (MKHE) which allows homomorphic evaluation on encrypted data under different keys can be one of the simplest solutions for a secure computation which handles multiple users' data. However, the current main problem of MKHE is that the dimension of its evaluated ciphertext relies on the number of users. To solve this problem, there are several variants of multikey homomorphic encryption schemes to keep the size of ciphertext constant for a fixed number of users. However, users interact one another before computation to provide their inputs, which increases setup complexity. Moreover, all the existing MKHE schemes and their variants have unique benefits which cannot be easily achieved at the same time in one scheme. In other words, each type of scheme has a suitable computational scenario to put its best performance. In this paper, we suggest more efficient evaluation key generation algorithm for the existing variants of MKHE schemes which have no ciphertext expansion for a fixed number of users. Our method only requires a very simple and minor pre-processing; distributing public keys, which is not counted as a round at all in many other applications. As a result, participants have less communication, computation, and memory cost in online phase. Moreover, we provide a practical conversion algorithm between the two types of schemes in order to \emph{efficiently} utilize both schemes' advantages together in more various applications. We also provide detailed comparison among similar results so that users can choose a suitable scheme for their homomorphic encryption based application scenarios.

Metadata
Available format(s)
PDF
Category
Cryptographic protocols
Publication info
Preprint. MINOR revision.
Keywords
Compact MKHEHomomorphic EncryptionMKHEMultikey Homomorphic Encryption
Contact author(s)
jungeun7430 @ naver com
History
2021-10-11: last of 2 revisions
2021-08-25: received
See all versions
Short URL
https://ia.cr/2021/1085
License
Creative Commons Attribution
CC BY
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