In mobile Ad Hoc networks, the existence and availability of trusted authorities is severely limited by intrinsic network features, and problems such as “service availability” have become a crucial issue. A proxy signature scheme allows an entity to delegate his/her signing capability to another entity in such a way that the latter can sign messages on behalf of the former when the former is not available. This is an important primitive to ensure the service availability issue. Proxy signatures have found numerous practical applications such as distributed systems, mobile agent applications, etc. However, the security of the known proxy signature schemes is proven in the random oracle which does not imply security in the real world. In this paper, we propose the first proxy signature schemes without random oracle. The unforgeability of our scheme is based on the hardness of the well known Computational Diffie Hellman (CDH) problem.