Generating Searchable Public-Key Ciphertexts with Hidden Structures for Fast Keyword Search

TL;DR

This paper introduces SPCHS, a new public-key encryption scheme that enables fast keyword search over large encrypted databases by structuring ciphertexts with hidden relations, maintaining semantic security.

Contribution

It proposes the first SPCHS scheme with hidden structures for efficient search, including a simple star-like construction and a generic construction from IBKEM, with security proofs.

Findings

Search complexity depends on matching ciphertexts, not total ciphertexts.

The scheme is semantically secure under standard cryptographic assumptions.

Efficient keyword search is achieved without sacrificing security.

Abstract

Existing semantically secure public-key searchable encryption schemes take search time linear with the total number of the ciphertexts. This makes retrieval from large-scale databases prohibitive. To alleviate this problem, this paper proposes Searchable Public-Key Ciphertexts with Hidden Structures (SPCHS) for keyword search as fast as possible without sacrificing semantic security of the encrypted keywords. In SPCHS, all keyword-searchable ciphertexts are structured by hidden relations, and with the search trapdoor corresponding to a keyword, the minimum information of therelations is disclosed to a search algorithm as the guidance to find all matching ciphertexts efficiently. We construct a simple SPCHS scheme from scratch in which the ciphertexts have a hidden star-like structure. We prove our scheme to be semantically secure based on the decisional bilinear Diffie-Hellman assumption in the Random Oracle (RO) model. The search complexity of our scheme is dependent on the actual number of the ciphertexts containing the queried keyword, rather than the number of all ciphertexts. Finally, we present a generic SPCHS construction from anonymous identity-based encryption and collision-free full-identity malleable Identity-Based Key Encapsulation Mechanism (IBKEM) with anonymity. We illustrate two collision-free full-identity malleable IBKEM instances, which are semantically secure and anonymous, respectively, in the RO and standard models. The latter instance enables us to construct an SPCHS scheme with semantic security in the standard model.