Low Complexity Multi-authority Attribute Based Encryption Scheme for Mobile Cloud Computing

In multi-authority attribute based encryption (MA-ABE) schemes, multiple authorities monitor different set of attributes and the corresponding shared-decryption-keys. In such schemes the encrypt or can encrypt a message and upload to the cloud, whereas only users who satisfy a set of attributes from each authority can decrypt that message. We extend the well-known Chase and Chow's scheme \cite{imaabe} for mobile users by introducing a cloud based semi-trusted-authority (STA) between the mobile user and attribute authorities. In this work, substantial amount of communications and computations are outsourced to the STA without compromising the security and privacy of the MA-ABE scheme. The STA interacts with the attribute-authorities on behalf of the user and obtains the masked shared-decryption-keys. Later the STA combines all the keys and gets one masked-key which can only be unmasked by a user to decrypt the message. In particular, STA cannot decrypt the message nor determine the attributes of the mobile user, hence, the security and privacy of the proposed MA-ABE scheme is preserved.