Comments on “Verifiable and Exculpable Outsourced Attribute-Based Encryption for Access Control in Cloud Computing”

Recently in IEEE Transactions on Dependable and Secure Computing (TDSC) (doi: 10.1109/TDSC.2015.2499755), Ma et al. proposed a new construction of attribute-based encryption (ABE) which can outsource the complicated encryption task to Encryption Service Provider (ESP) in a verifiable manner. Despite the authors claimed that the results of the outsourced encryption can be checked by the user, we show that Ma et al.'s proposal fails to provide the verifiability property for outsourced encryption, the most essential security goal that a verifiable computation scheme should achieve. Specifically, by giving concrete attacks, we demonstrate that the ESP can return forged intermediate ciphertext to the user without being detected.