Wireless network was one of the most popular, vibrant and active field of communication in computing industry in the past decade but in the present times researchers are ardently interested in exploration of solutions to various challenges over ad hoc networks. The solution to achieve secure routing over ad hoc networks has been taken into consideration in this paper. Security in ad hoc networks is difficult to achieve because of the vulnerability of wireless links, mobility of nodes, dynamic network topology, limited physical protection of nodes, absence of a certification authority, and the lack of a centralized infrastructure. Moreover the ad hoc environment is accessible to both legitimate network users and unfortunately to malicious attackers. The major problem in ad hoc networks arise when a new mobile node joins the network and it does not have any trust based relationship with other nodes in the network. In this paper, implementation of Diffie-Hellman algorithm of key exchange has been presented which can be integrated into any of the on-demand MANET routing protocol so as to make it secure.