Security for information data broadcasting system with conditional-access control

The security of the key distribution scheme for the broadcasting system with conditional-access control is discussed and proposals are made for the realization of the secure key distribution scheme. First, it is shown that known-plaintext attack, which is a very powerful attack, can be made to the conventional systems. Then a proposal is made on the key distribution system which is free from the known-plaintext attack. Next, the information data broadcasting system which accommodates multiple information transmitters is discussed and it is pointed out that the system can be endangered if one of the information providers loosely manages the secret information of the receivers. Two systems are proposed, then, to solve the problem and to protect the system