Patent ID: 7395425
Filing Date: 2008-07-01
Classification: G06F,G11B,H04L,H04N

Abstract:
1. A data protection system that comprises three or more terminals, an encryption device, and an encryption key designation device, and that protects distribution data that is to be distributed to said terminals, according to said encryption device encrypting the distribution data, wherein: each terminal is operable to said encryption key designation device is operable to designate encryption keys, and includes: an invalid terminal designation unit for designating one or more terminals as invalid terminals; and an encryption key designation unit for designating, when all the decryption keys assigned to the terminals, other than decryption keys assigned to the one or more invalid terminals, are prescribed as valid decryption keys, and when a procedure for selecting an assigned valid decryption key for the most terminals not designated as invalid terminals is repeated until all terminals not designated as invalid terminals have been assigned a selected valid decryption key, encryption keys that respectively correspond to each of the valid decryption keys that are selected as a result of the procedure; and said encryption device includes an encryption unit for encrypting distribution data by successively using all the designated encryption keys to encrypt distribution data, generating the encrypted distribution data group, and outputting the generated encrypted distribution data group.