Dynamic Broadcast Encryption Scheme with Revoking User

Currently, there still lacks an efficient methodology to revoke user＇s ability to decrypt ciphertext in broadcast encryption with the uncertain number of ciphertext recipients. To solve this problem, here, we present a dynamic broadcast encryption scheme with the following properties： First, the length of the ciphertext has a linear relationship with the number of revocable users, but it has no association with the total number of ciphertext recipients. Sec- ond, the scheme also works when users dynamically join. Espe- cially, compared with methods published up to date, our scheme is more efficient with a large number of ciphertext recipients. Third, the broadcaster can revoke user＇s ability to decrypt ciphertext if necessary. Fourth, the private key of users is composed of three elements in Elliptic curve group of prime order. Last, if q-Deci- sional Multi-Exponent Bilinear Diffie-Hellman assumption holds, our scheme is secure in the standard model when a polynomial time adversary selectively attacks it.

Access control scheme with tracing for outsourced databases

To manage dynamic access control and deter pi- rate attacks on outsourced databases, a dynamic access control scheme with tracing is proposed. In our scheme, we introduce the traitor tracing idea into outsource databases, and employ a polynomial function and filter function as the basic means of constructing encryption and decryption procedures to reduce computation, communication, and storage overheads. Compared to previous access control schemes for outsourced databases, our scheme can not only protect sensitive data from leaking and perform scalable encryption at the server side without shipping the outsourced data back to the data owner when group membership is changed, but also provide trace-and-revoke features. When malicious users clone and sell their decryption keys for profit, our scheme can trace the decryption keys to the malicious users and revoke them. Furthermore, our scheme avoids massive message exchanges for establishing the decryption key between the data owner and the user. Compared to previously proposed publickey traitor tracing schemes, our scheme can simultaneously achieve full collusion resistance, full recoverability, full revocation, and black-box traceability. The proof of security and analysis of performance show that our scheme is secure and efficient.