On Extension of Evaluation Algorithms in Keyed-Homomorphic Encryption

Hirotomo Shinoki, Koji Nuida

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Homomorphic encryption (HE) is public key encryption that enables computation over ciphertexts without decrypting them, while it is known that HE cannot achieve IND-CCA2 security. To overcome this issue, the notion of keyed-homomorphic encryption (KH-PKE) was introduced, which has a separate homomorphic evaluation key and can achieve stronger security (Emura et al., PKC 2013). The contributions of this paper are twofold. First, the syntax of KH-PKE assumes that homomorphic evaluation is performed for single operations, and its security notion called KH-CCA security was formulated based on this syntax. Consequently, if the homomorphic evaluation algorithm is enhanced in a way of gathering up sequential operations as a single evaluation, then it is not obvious whether or not KH-CCA security is preserved. In this paper, we show that KH-CCA security is in general not preserved under such modification, while KH-CCA security is preserved when the original scheme additionally satisfies circuit privacy. Secondly, Catalano and Fiore (ACM CCS 2015) proposed a conversion method from linearly HE schemes into two-level HE schemes, the latter admitting addition and a single multiplication for ciphertexts. In this paper, we extend the conversion to the case of linearly KH-PKE schemes to obtain two-level KH-PKE schemes.

Original languageEnglish
Title of host publicationAdvances in Information and Computer Security - 17th International Workshop on Security, IWSEC 2022, Proceedings
EditorsChen-Mou Cheng, Mitsuaki Akiyama
PublisherSpringer Science and Business Media Deutschland GmbH
Number of pages19
ISBN (Print)9783031152542
Publication statusPublished - 2022
Event17th International Workshop on Security, IWSEC 2022 - Tokyo, Japan
Duration: Aug 31 2022Sept 2 2022

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume13504 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349


Conference17th International Workshop on Security, IWSEC 2022

All Science Journal Classification (ASJC) codes

  • Theoretical Computer Science
  • Computer Science(all)


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