A method of managing a key of a user for a broadcast encryption. The method includes forming a tree comprising m hierarchies by repeating a process of setting a ith level comprising groups into which at least one node is grouped in a unit of ni, and setting a i+1th level comprising the groups of the ith level that are re-grouped in a unit of ni+1 until i is from “1” to “m”. The method further includes mapping users on at least one node of the tree and message providers on the mth hierarchy, going down from the mth hierarchy to the first hierarchy to map key encryption keys with respect to the i+1th level connected to the ith level, and transmitting the message using the key encryption keys.