Ciphertext policy-hiding attribute-based encryption

Ciphertext-policy attribute based encryption (CPABE) is becoming very important in distributed computing environment, because it makes easier to protect, broadcast and control the access of information, especially over the cloud server. In CP-ABE every plaintext is encrypted under an access structure, defined on the user´s attribute and users have given private keys in advance from the trusted and reliable authority. If the user´s attributes satisfy the access structure then only user can decrypt the ciphertext using his/her private keys. But, there is one privacy issue in available CP-ABE schemes, owner sends the access structure along with the ciphertext and everyone can learn the access policy. Sometimes this access structure violates the privacy of the ciphertext, i.e. it reveals the type of information the ciphertext contains and sometimes reveals the partial anonymity of the decryptor. It is desirable to hide the access structure associated to the ciphertext, especially in the medical database cloud server applications. Previous CP-ABE schemes hides only plaintext through encryption. There are few CP-ABE schemes which hides access structure (policy) as well but are not efficient in terms of computations. We proposed a secure CP-ABE scheme using composite-order bilinear groups which hides access policy.