Patent ID: 7283633

Claim:
An information recording device for recording the information on a recording medium, comprising: memory means for holding a node key unique to each node of a hierarchical tree structure having a plural number of such information recording devices, operating as leaves, and a leaf key unique to each information recording device, said memory means also holding a key renewal block formed as renewal key storage data decryptable using at least one of the node key and the leaf key; and encryption means for decrypting the key renewal block decryptable using at least one of the node key and the leaf key provided in said information recording device to calculate an encrypting key used in encrypting data to be stored in said recording medium; said encryption means encrypting the data to be stored in said recording medium using the calculated encrypting key; said encryption means detecting, in encrypting and storing content for said recording medium, the latest usable key renewal block from key renewal blocks stored in said recording medium and from the key renewal block stored in said memory means of the information recording device itself; said encryption means encrypting the data to be stored on said recording medium using the encrypting key obtained on decrypting the detected latest usable key renewal block, wherein said information recording device executes processing of writing the latest usable one of the key renewal blocks stored on said recording medium and the key renewal block stored in the memory means of the information recording device itself, in the memory means of the information recording device itself, in case the latest usable key renewal block is the key renewal block stored in the recording medium and the latest key renewal block is not as yet stored in the memory means of the information recording device itself, and wherein said information recording device executes the processing of writing the latest usable one of the key renewal blocks stored on said recording medium and the key renewal block stored in the memory means of the information recording device itself on the recording medium in case the latest usable key renewal block is the key renewal block stored in the memory means of the information recording device itself and the latest key renewal block is not as yet stored on the recording medium.