In contrast with traditional networks, with the characteristics of mobile wireless devices that can dynamically form a network without any infrastructure and wired line, mobile ad hoc networks usually do not provide on-line access to trusted authorities or to centralized servers. Furthermore, they frequently exhibit partition that is due to link and node failures and node mobility. For these reasons, if we apply traditional PKI Public Key Infrastructure) security architecture to mobile ad hoc networks, it will appear secure blind sides especially in large-scale ad hoc networks. For this point of view, we propose a new scalable cluster-organized key management scheme and distribution of trust to an aggregation of nodes by taking advantage of threshold cryptosystems faculty to perform key management. Furthermore, our approach provides robust CA (Certificate Authority) fault tolerance mechanism to keep off single failure point CA, improves the key exchange performance and security, and enhances the secure routing.