Patent ID: 7210042
Filing Date: 2007-04-24
Classification: G06F

Abstract:
1. A revoke control method for revoking at least one of a plurality of content utilizing devices, each of the content utilizing devices being assigned a device ID and assigned a set of device keys according to the device ID, the device ID being formed of numerals each indicating a position of each of the device keys of the set in each one dimensional array of a device key matrix in which device keys are arranged in a two dimensional manner, and the device ID indicating a path in a plurality of trees that are formed of all possible combinations of device keys in the device key matrix, the method comprising: preparing the device key matrix; inputting a revoke target path, which is a path to be revoked in the trees and formed of numerals each indicating a position of a device key in each one dimensional array of the device key matrix; calculating a boundary set of paths except for the revoke target path in the trees, each of the paths of the boundary set being formed of one or more numerals each indicating a position of a device key in each one dimensional array of the device key matrix; calculating a path function value corresponding to each of the paths of the boundary set based on each device key indicated by each numeral of the each of the paths of the boundary set, to obtain a plurality of path function values corresponding to the paths of the boundary set; encrypting a master key by using each of the path function values, to obtain a plurality of encrypted data items corresponding to the paths of the boundary set; generating revoke control data including the encrypted data items; outputting the revoke control data to each of the content utilizing devices; and decrypting, by each content utilizing device whose device ID indicates one of the boundary set of paths, one of the encrypted data items by using a path function value calculated based on one or more device keys of the set assigned to the each content utilizing device.