Patent ID: 8200963

Claim:
A broadcast encryption method comprising: generating, by a server, a base group of unique base values, each of the base values generated from a unique combination of integers among a plurality of different integers having values greater than 1, and assigning a first base value among the unique base values to a first user and a second base value among the unique base values to a second user; generating first secret information and second secret information for the first user and the second user through calculations with key value information allocated to a corresponding user by using the first base value and the second base value as a base, respectively, and sending the secret information to the first user and the second user; generating an inverse-base parameter value through calculations with an integer used to produce the base group and key value information of the first user and the second user, and sending the produced inverse-base parameter value and key value information to the first user and the second user; and deriving a first group key and a second group key based on the key value information and the first secret information and the second secret information, respectively, encrypting a session key with the derived first group key and second group key and sending the encrypted session key encrypted with the derived first group key and the encrypted session key encrypted with the derived second group key to the first user and the second user, respectively.