Paper 2023/665

On the Feasibility of Identity-based Encryption with Equality Test against Insider Attacks

Keita Emura, Kanazawa University

Public key encryption with equality test, proposed by Yang et al. (CT-RSA 2010), allows anyone to check whether two ciphertexts of distinct public keys are encryptions of the same plaintext or not using trapdoors, and identity-based encryption with equality test (IBEET) is its identity-based variant. As a variant of IBEET, IBEET against insider attacks (IBEETIA) was proposed by Wu et al. (ACISP 2017), where a token is defined for each identity and is used for encryption. Lee et al. (ACISP 2018) and Duong et al. (ProvSec 2019) proposed IBEETIA schemes constructed by identity-based encryption (IBE) related complexity assumptions. Later, Emura and Takayasu (IEICE Transactions 2023) demonstrated that symmetric key encryption and pseudo-random permutations are sufficient to construct IBEETIA which is secure in the previous security definition. In this paper, we demonstrate a sufficient condition that IBEETIA implies IBE. We define one-wayness against chosen-plaintext/ciphertext attacks for the token generator (OW-TG-CPA/CCA) and for token holders (OW-TH-CPA/CCA), which were not considered in the previous security definition. We show that OW-TG-CPA secure IBEETIA with additional conditions implies OW-CPA secure IBE. On the other hand, we propose a generic construction of OW-TH-CCA secure IBEETIA from public key encryption. Our results suggest a design principle to efficiently construct IBEETIA without employing IBE-related complexity assumptions.

Available format(s)
Cryptographic protocols
Publication info
Published elsewhere. Minor revision. ACISP 2024
IBEET against insider attacksSearchable EncryptionGeneric Construction
Contact author(s)
k-emura @ se kanazawa-u ac jp
2024-04-15: last of 3 revisions
2023-05-11: received
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      author = {Keita Emura},
      title = {On the Feasibility of Identity-based Encryption with Equality Test against Insider Attacks},
      howpublished = {Cryptology ePrint Archive, Paper 2023/665},
      year = {2023},
      note = {\url{}},
      url = {}
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