The recent IEEE 802.16j-2009 adds multi-hop relay capabilities to IEEE 802.16 systems, which aims to offer improved coverage and capacity over single-hop radio access systems. In this paper, we point out several security issues, including non-authenticated privacy and key management messages, insecure relay multicast rekeying algorithm and insecure Multicast and Broadcast Rekeying Algorithm (MBRA), of the key management protocols in IEEE 802.16j-2009 and give some solutions. In particular, we propose a new Secure MBRA (SMBRA) based on identity and logical key tree to solve the security issues of MBRA. SMBRA can not only provide backward and forward secrecy of communications but also avoid key forgery. Furthermore, our theoretical analysis and simulation indicate that SMBRA is much more efficient and adequate, especially in a large group.

The security of P2P networks depends on building trust management among peers. However, current trust management models focus on preventing untrustworthy resources from spreading by malicious providers, but have few effects on reducing denial-of-service attacks of malicious consumers and free riding of selfish peers. Pointing to these problems, a bi-evaluation trust management model, called BiTrust, is proposed. In this model, the trustworthiness of a peer is divided into service and request trustworthiness. Service trustworthiness shows the resources reliability of providers, and request trustworthiness is used to deal with requests from consumers, which can keep away malicious consumers and encourage selfish peers to share resources. A generic method for evaluating service and request trustworthiness is described. Furthermore, the implementation strategies of the model are also depicted in this paper. The following analysis and simulation show that BiTrust is more effective on enhancing high-quality resources sharing among peers and more advanced in successful exchanges rate.