In the cloud computing context, group data sharing, which is highly convenient for people who intend to share data with multiple members of a group, has attracted extensive research attention. However, the question of how data security might be ensured in this scenario, particularly as regards the security of group session keys, still remains an open one. To support secure group data sharing in cloud computing, it is essential to design a key agreement protocol characterized by both high flexibility and efficiency. Accordingly, this paper proposes a key agreement protocol based on Latin Square to reinforce the security of group data sharing. This protocol supports an arbitrary number of members to participate in a group and make equal contributions to generating a common session key among themselves. Compared with previous works, both the communication and the computational complexity in this protocol are significantly reduced. In addition, the services of authentication, key confirmation and fault tolerance are provided, enabling the protocol to resist different types of attacks. The results of both theoretical and experimental analysis indicate that the proposed protocol can efficiently support secure cloud data sharing for large-scale groups.

Subscription-based services, where broadcasting companies make profits by providing subscription programs to users, have become a popular application of wireless broadcast systems. Driving by business interests and data security, companies usually encrypt content of programs with session keys, then only authorized users can access the contents of their subscribed programs, respectively. It is challenging to flexibly distribute and update the session key, we are therefore motivated to propose an identity-based many-to-many subscription scheme (IMS) with efficient key management. The IMS scheme possesses three novel advantages: First, it provides a whole set of subscription flow, from the selection of programs of interest to the generation and updating of keys. Second, it supports program updating and all subscription behaviors. Third, it employs a signature and authentication mechanism to stipulate that only authorized users can access the programs’ ciphertext. The theoretical analysis demonstrates that the proposed scheme is secure against chosen-ciphertext attacks (CCA) under the$ k$-bilinear Diffie-Hellman exponent (BDHE) problem, and has a decent performance in storage and computational overhead. The experimental analysis shows the total time cost of the proposed scheme is reduced more than 75.02 percent compared against the popular peer schemes under the condition of 2500 users.

The vehicular ad hoc network (VANET) is a type of mobile wireless networks, where vehicles are allowed to broadcast a message to its neighbors and access data from other participants. However, how to guarantee the reliability of these broadcast messages and prevent malicious vehicles from accessing the private data of the VANETs is still an open problem to be solved. As a countermeasure, a fuzzy-based trustworthiness evaluation scheme for privilege management in VANETs is proposed in this article. In the proposed scheme, to ensure the result of trustworthiness is valid, mutual authentication with conditional anonymity between the evaluator and the vehicle to be evaluated is first employed. Then, based on the vehicle's behavioral big data, the trustworthiness of each vehicle is evaluated by utilizing the fuzzy theory. Note that the privilege of a vehicle and the reliability of the vehicle's messages are determined by its trustworthiness. Moreover, the mobility of vehicles is also considered in this article, since the location of a vehicle is not constant and the monitoring area of an road side unit is limited. The results of theoretical and experimental analyses demonstrate that the proposed scheme performs well in terms of security and efficiency.