In recent years, security in MANET is anticipated as the pre-establishment of specific information among the participating nodes, so that the future communications can be secured through a newly designed protocol, which deploys cryptographic mechanisms over the pre-established information. In this paper we suggest three dimensions to secure the communications in wireless mobile ad hoc networks. Then we demonstrate the issues that might creep out in the security design, when a cryptographic technique alone is involved. Also we suggest how to counter those issues through the combination of trust management with cryptographic mechanisms. Moreover, we propose the need to introduce the notion of heterogeneity resource management in the security design to address the divergence among the nodes, which can be taken advantage to diminish the packet drop attacks.