Patent ID: 7568094

Claim:
A content providing system which receives an encryption key corresponding to decryption keys assigned to a plurality of user systems from a third-party unit and provides encrypted content and header information to decrypt the encrypted content to each of said plurality of user systems, the decryption key being a value obtained by substituting user identification information unique to a user system into a key generation polynomial assigned to each sub-group to which a plurality of pieces of user identification information belong, the content providing system comprising: a content encrypting device configured to encrypt content using a session key and obtain the encrypted content; a header information generating device configured to encrypt the session key using the encryption key and generate header information which includes the obtained encrypted session key and one or more values based on user identification information about at least one of the user systems which are permitted to obtain the session key; and a transmission device configured to transmit the encrypted content and at least a portion of the header information to each of the user systems.