Method for data transmission

摘要

The invention relates to a method for transmitting data to a subset of users via a radio medium. The users are managed as leaves of a tree structure consisting of a root, knots and leaves. Keys are allocated to the knots and leaves of the tree structure. The users have the keys allocated to their leaf and the knots on the path between their leaf and the root. The data to be transmitted is encoded in such a way that it can be decoded respectively by the key to the knots which are closest to the root, the direct and indirect successors of said knots being only users belonging to the subset. The data can also be decoded by the keys which are allocated to the users belonging to the subset, the path between said users and the root containing no such knots.