In this paper, the authors propose an efficient and simpler Contributory Group Key Agreement protocol (CGKA) based on Elliptic Curve Diffie Hellman (ECDH). In this CGKA protocol, a member acts as a Group Controller (GC) and forms two-party groups with remaining group members and generates an ECDH style shared key per each two-party group. It then combines these keys into a single group key and acts as a normal group member. This paper also addresses a Dynamic Contributory Group Key Agreement protocol (DCGKA) by extending CGKA to dynamic groups.