A Mobile Ad-Hoc NETwork (MANET) is a self-organized network, with no fixed infrastructure, limited resources and limited physical security. Security in such an environment is an essential requirement. Key management is a salient element in MANET security. It is responsible for key generation, storage, distribution, updating, revocation, deleting and archiving. Key management protocols are classified into symmetric, asymmetric, group and hybrid. Group key management is a point of interest for researchers with the growing usage of mobile devices and the rising of multicast communication.