An Anonymous Multi-Authority Key-Policy Attribute-Based Encryption Scheme With Expressive Keyword Search

Existing attribute-based searchable encryption schemes have advanced the ability to perform fine-grained keyword retrieval over encrypted data; however, they still suffer from two fundamental limitations. First, most existing constructions rely on a single trusted authority, which not only results in excessive computational burden on the centralized entity but also limits the scalability of key management in distributed environments. Second, many schemes reveal sensitive attribute or policy information in ciphertexts or search tokens, causing privacy leakage and enabling inference attacks from untrusted servers. These shortcomings highlight the need for a decentralized and privacy-preserving searchable encryption framework capable of supporting expressive queries without exposing access structures or user attributes. To overcome these limitations, we first design an anonymous Multi-Authority Key-Policy Attribute-Based Encryption (MA-KPABE) scheme. Our construction conceals the access policies embedded in users' secret keys and attribute embedded in the ciphertext, thereby limiting information leakage during key generation. Building upon this foundation, we further extend MA-KPABE into a Multi-Authority Attribute-Based Searchable Encryption (MA-ASE) scheme that integrates expressive keyword search capabilities while preserving keyword privacy. The resulting system enables decentralized key management, privacy-preserving access control, and secure expressive search within a unified cryptographic framework. We formally prove that the proposed schemes satisfy IND-CPA, anonymity, and IND-CKA security. Comprehensive performance evaluations demonstrate that the distributed architecture significantly reduces authority-side computational load and achieves practical efficiency for large-scale encrypted retrieval scenarios.