Open IPTV has attracted considerable attention and is expected to bring great changes in the IPTV service area. However, because of its openness and IP network characteristics, security is one of the major issues hindering its commercialization. For IPTV, several security mechanisms for user authentication and content protection have been applied to make the service reliable. These traditional security mechanisms cannot be adopted in the IPTV area, because in the many-to-many environment the security and hence the system performance is influenced by numerous factors. In our work, we propose a mechanism for secure user authentication and key distribution based on Kerberos for open IPTV and for secure M2M three-screen service in home networks. Our proposal provides an efficient authentication process and secure transfer of contents among users, and it further decreases the authentication time compared with the other mechanisms.