Attribute-Based Proxy Re-Encryption (ABPRE) schemes facilitate secure data sharing based on user attributes without needing a centralized authority for encryption or re-encryption. However, many ABPRE models lack built-in support for efficient keyword search and dynamic keyword updating, often depending on a Private Key Generator (PKG). To overcome this, Ge et al. proposed the CPAB-KSDS scheme, a cipher text-policy ABPRE framework that enables secure keyword searches and keyword updates without PKG involvement. They assert that CPAB-KSDS achieves indistinguishability under chosen-cipher text attacks (IND-CCA) and chosen-keyword attacks (IND-CKA) within the random oracle model.

A detailed security analysis of Ge et al.’s CPAB-KSDS scheme, revealing critical flaws in their security reductions from IND-CKA to underlying assumptions. Additionally, we demonstrate a specific attack that breaches the IND-CKA security of CPAB-KSDS. Our results indicate that CPAB-KSDS fails to achieve the claimed IND-CKA security, exposing significant vulnerabilities in encryption schemes that incorporate keyword search and update features.

Keywords: Cryptanalysis, Attribute-Based Encryption, Proxy Re-Encryption, Searchable Encryption, Keyword Update, Indistinguishability, Security Flaws.