Publication Type

Conference Proceeding Article

Version

acceptedVersion

Publication Date

7-2025

Abstract

Proxy re-encryption (PRE) schemes enable a semi-honest proxy to transform a ciphertext of one user i to another user j while preserving the privacy of the underlying message. Multi-hop PRE schemes allow a legal ciphertext to undergo multiple transformations, but for lattice-based multi-hop PREs, the number of transformations is typically bounded due to the increase of error terms. Recently, Zhao et al. (ESORICS 2024) introduced a lattice-based unbounded multi-hop (homomorphic) PRE scheme that supports an unbounded number of hops. Nevertheless, their scheme only achieves the selective CPA security. In contrast, Fuchsbauer et al. (PKC 2019) proposed a generic framework for constructing HRA-secure unbounded multi-hop PRE schemes from FHE. Despite this, when instantiated with state-of-the-art FHEW-like schemes, the overall key size and efficiency remain unsatisfactory.In this paper, we present a lattice-based unbounded multi-hop PRE scheme with the stronger adaptive HRA security (i.e. security against honest re-encryption attacks), which is more suitable for practical applications. Our scheme features an optimized re-encryption process based on the FHEW-like blind rotation, which resolves the incompatibility between the noise flooding technique and Fuchsbauer et al. ’s framework when instantiated with FHEW-like schemes. This results in reduced storage requirements for public keys and offers higher efficiency. Moreover, our optimized unbounded multi-hop PRE scheme can be modified to an unbounded homomorphic PRE, which allows for arbitrary homomorphic computations over fresh, re-encrypted, and evaluated ciphertexts.

Keywords

proxy re-encryption, unbounded multi-hop, HRA security, LWE

Discipline

Information Security

Research Areas

Information Systems and Management

Areas of Excellence

Digital transformation

Publication

Proceedings of the 30th Australasian Conference, ACISP 2025, Wollongong, Australia, July 14-16

First Page

124

Last Page

144

ISBN

9789819690985

Identifier

10.1007/978-981-96-9098-5_7

Publisher

Springer

City or Country

Cham

Additional URL

https://doi.org/10.1007/978-981-96-9098-5_7

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