Prof. Niv Gilboa

We propose a new and efficient scheme for broadcast encryption. A broadcast encryption system allows a broadcaster to send an encrypted message to a dynamically chosen subset ,of a given set of users, such that only users in this subset can decrypt the message. An important component of broadcast encryption schemes is revocation of users by the broadcaster, thereby updating the subset . Revocation may be either temporary, for a specific ciphertext, or permanent. We present the first public key broadcast encryption scheme that support permanent revocation of users. Our scheme is fully collusionresistant. In other words, even if all the users in the network collude with a revoked user, the revoked user cannot encrypt messages without receiving new keys from the broadcaster. The procedure is based on Cipher-text Policy Attribute-Based Encryption (CP-ABE). The overhead of our system is Ο in all major performance
measures including length of private and public keys, computational complexity, user’s storage space, and computational complexity of encryption and decryp