A Type-3 Pairing-Based Attribute-Based Encryption Scheme with Expressive Keyword Search and Trapdoor Delegation

Abstract

Cloud data sharing allows users to outsource data storage and management to external servers, but it also raises privacy concerns when data must remain encrypted while still supporting efficient search and fine-grained access control. Attribute-based encryption with keyword search (ABE-EKS) addresses this problem by combining searchable encryption with attribute-based access policies. However, existing schemes often focus on separate aspects such as expressive search, online/offline computation, revocation, or policy protection, while controlled trapdoor delegation and inequality-based keyword predicates are less commonly considered together in an implementation-oriented Type-3 pairing setting. This paper revisits the ABE-EKS framework of Yang et al. and adapts it to the Type-3 pairing setting. The construction follows the main structure of Yang et al.’s ABE-EKS scheme, but places the group elements in the appropriate source groups for asymmetric pairings. It further supports expressive access-control and keyword-search policies, Boolean keyword predicates, inequality comparisons, and trapdoor key delegation. We also analyse its security under the honest-but-curious cloud model and implement the scheme using the Apache Milagro Cryptographic Library (AMCL). Experimental results on the Enron Email dataset demonstrate the feasibility of the proposed construction for outsourced encrypted data-sharing scenarios.