Patent ID: 8341403

Claim:
A revocation examination method for a device, the method comprising: storing, in a decryption support device, information that indicates revoked nodes among a plurality of nodes in a node tree; receiving, by the decryption support device, from a device other than the decryption support device, a revocation examination request message including an ID of a leaf node in the node tree corresponding to the device, the revocation examination request message requesting the decryption support device to examine whether only at least one key allocated to the device corresponding to the ID of the leaf node is revoked; examining, by the decryption support device, whether only the at least one key allocated to the device corresponding to the ID of the leaf node is revoked with reference to the information; transmitting, by the decryption support device, a response to the revocation examination request message that indicates whether only the at least one key allocated to the device corresponding to the ID of the leaf node is revoked based on a result of the examining, receiving a random number from the device; and establishing a secure authenticated channel (SAC) with the device based on the random number, wherein the establishing the SAC generates a session key between the device and the decryption support device based on the random number so as to establish the SAC by using the generated session key.