Ad hoc networks have lots of applications; however, a vital problem concerning their security aspects must be solved in order to realize these applications. The dynamic and cooperative nature of ad hoc networks present challenges in securing these networks. There are recent research efforts in securing ad hoc networks. Amongst security approaches, there are threshold cryptography, certification authority, reputation and authentication., in this paper we introduce and survey these aprroaches. We conclude this paper and identify the challenges and open research areas associated with each of these approaches.