Abstract: A recording device which backs up a content ? in a recording medium and a recording device which restores the content are registered in a server so as to belong to the same domain group. When the recording device tries to restore the content, the restore is permitted only when both the recording devices belong to the same domain group. When there is a refresh request of the domain group, the domain group is invalidated only when a refresh period has passed. When a refresh number recorded in the recording device is less than or equal to the refresh number recorded in the recording device, the recording device backs up and locally merges the content recorded in the recording device into the recording medium.

Abstract: A data processing apparatus capable of updating and writing a plurality of distributed information items generated based on to-be-held secret information with respect to a data storage device in which access is not limited includes a secret distribution processing portion which generates a plurality of distributed information items updated this time according to secret information to be held this time based on a threshold value secret distribution method, and a distributed information management portion which selects recording positions of distributed information items updated this time to leave behind distributed information items of a number less than a threshold value among a plurality of distributed information items updated last time with respect to a plurality of distributed information items updated and stored in the data storage device and writes distributed information items updated this time to the data storage device based on the selected recording positions.