The integration of different wireless networks such as cellular networks, WLANs and MANETs with a core IP network is an extremely complex and challenging task, involving issues at all layers of the protocol stack. It is expected that the future advancements in such an integrated heterogeneous network technology would provide a variety of services to the network users. For achieving the end- to- end security in a heterogeneous network environment, an integrated and robust security framework is to be developed and for that an efficient and decentralized key establishment scheme is a fundamental requirement. This paper proposes a hierarchical and decentralized key establishment scheme applying the principles of symmetric polynomials for the futuristic heterogeneous network environment.