An encryption scheme for a secure policy updating

Ciphertext policy attribute based encryption is an encryption technique where the data is encrypted according to an access policy over attributes. Users who have a secret key associated with a set of attributes which satisfy the access policy can decrypt the encrypted data. However, one of the drawbacks of the CP-ABE is that it does not support updating access control policies without decrypting the encrypted data. We present a new variant of the CP-ABE scheme called ciphertext policy attribute based proxy re-encryption (CP-ABPRE). The proposed scheme allows to update the access control policy of the encrypted data without decrypting the ciphertext. The scheme uses a semitrusted entity called proxy to re-encrypt the encrypted data according to a new access control policy such that only users who satisfy the new policy can decrypt the data. The construction of our scheme is based on prime order bilinear groups. We give a formal definition for semantic security and provide a security proof in the generic group model.