Fully secure ciphertext-policy attribute based encryption with security mediator
Attribute-Based Encryption (ABE) offers fine-grained decryption policy such that users can do decryption if their attributes satisfy the policy. Such flexibility enables it applicable in various applications in government and business. However, there are two issues that should be solved first before it is deployed in practice, namely user revocation and decryption outsourcing. In this paper, we adopt the slightly modified Lewko et al.'s fully-CCA-secure Ciphertext-Policy-ABE (CPABE) combining with Boneh et al.'s idea of mediated cryptography to propose a CP-ABE with SEcurity Mediator (SEM) supporting immediate user revocation. At the same time, by the introduce of SEM, we intendedly outsource most of the computation workload in decryption to SEM side and leave only one exponentiation and one division at user side for decryption. It is proved fully-RCCA-CCA-secure in random oracle model.