US Patent 11522722 Communication apparatus and communication method

A communication apparatus configured to acquire information in a distributed ledger shared in a network, the communication apparatus includes a memory; and a processor coupled to the memory and configured to acquire one or more digital certificates used by a user of another apparatus to apply to the communication apparatus from the other apparatus, acquire type information that identifies a combination of the user and the type of information certified by the one or more digital certificates, by using the distributed ledger, acquire certificate issue history that is recorded in the distributed ledger in association with the type information, and determine whether the issue history contains information of another digital certificate that has not been acquired from the other apparatus.