Combination-based broadcast encryption method

A broadcast encryption method comprising:

• grouping, by a server, into a plurality of groups one upper group of a plurality of users receiving a broadcast message, and assigning a key value to corresponding users of each group;
• generating a base group for each group through combinations of integers of a plurality of different integers having values greater than 1, and assigning users of each group the base group produced through a different combination;
• generating secret information for each user through calculations with key value information allocated to a corresponding user of each group by using the base group allocated to each user as a base, and sending the secret information to each user;
• generating an inverse-base parameter value through calculations with integers used to produce the base group and key value information of at least one privileged user, and sending the inverse-base parameter value to users of a corresponding group, in order for only the at least one privileged user of the plurality of users to eliminate the base group from the secret information;
• and deriving a group key for each group with the key value information of the at least one privileged user, encrypting a session key with the group key, and sending the encrypted session key to each user.

A broadcast encryption method comprising:

• generating a base group through combinations of integers of a plurality of different integers having values greater than 1, and allocating the base group generated through different combinations to each user of a plurality of users;
• generating secret information for each user through calculations with a key value information allocated to a corresponding user based on the base group allocated to each user, and receiving by each user from a server the secret information;
• generating an inverse-base parameter value through calculations with integers used to produce the base group and the key value information of one or more privileged users, and receiving by each of the users the produced inverse-base parameter value, in order for only the privileged users of the plurality of users to eliminate the base group from the secret information;
• generating a group key by using the secret information for each user received from the server and the inverse-base parameter value;
• and decrypting, by a processor of each user, a session key received from the server by using the group key.

A broadcast encryption method comprising:

• grouping into a plurality of groups one upper group having a plurality of users receiving a broadcast message, and assigning a key value to users of each group;
• generating a base group for each group through combinations of integers of a plurality of different integers having values greater than 1, and assigning each user of each group the base group produced through a different combination;
• generating secret information for each user through calculations with key value information assigned to users of each group by using as a base the base group assigned to each user, and receiving by each user from a server the produced secret information for each user;
• generating an inverse-base parameter value through calculations with the integers used to produce the base group and the key value information of at least one privileged user of the plurality of users, and receiving from the server the inverse-base parameter value by users of each corresponding group, in order for only the at least one privileged user to eliminate the base group from the secret information;
• generating a group key for each group based on the secret information for each user received from the server and the inverse-base parameter value;
• and decrypting, by a processor of each user, a session key received from the server based on the group key for each group.