The public key encryption with keyword search (PEKS) scheme is a cryptographic primitive that allows a cloud server to search for a ciphertext without knowing the corresponding keyword used in the search.An expressive PEKS scheme is a variant of the PEKS scheme that supports conjunctive and disjunctive searches (expressive search).Utilising the expressive properties of an attribute-based Collections encryption (ABE) scheme, most of the expressive PEKS schemes can be constructed from an ABE scheme.In this paper, we first give a brief review of the transformed expressive PEKS scheme by Shen et al.
in 2019.Then, we present a keyword guessing attack on Shen et al.’s transformed expressive PEKS scheme and Trash Compactor show that an adversary can correctly guess the supposedly hidden keyword.