Networks where end-to-end connectivity and seamless access to nodes are not possible generally belong to the category of Delay Tolerant Networks (DTNs). Several security goals including authentication, access control and confidentiality have to be achieved. Existing security mechanisms based on Public Key Infrastructure (PKI) and Identity Based Cryptography (IBC) are not complete solutions for DTN. Since these mechanisms are most suitable for end-to-end communications. This paper focus on key exchange algorithm for DTN, the exchanged key can be used for subsequent encryption and authentication.