Access control for mobile multicast

An access control method for controlling access to a multicast delivery tree (3), in e.g. an IPv4 or an IPv6 network, comprising: performing, at a designated router (6, 10), authorization procedures for access to the delivery tree (3), the designated router (6, 10) being a multicast edge router of the multicast delivery tree. The designated router (6, 10) performs the authorization procedures by comparing authorization information received from a user (4, 8) with information received from a group manager (12). For sender access control, the verification information is based on a sender key provided by the group manager (12) to legitimate senders. For receiver access control, the verification information is based on a group key provided by the group manger (12) to a group of users. A derived value of the key, obtained by applying a derivation function to the key, may be used. The derivation function may be a one-way hash function.