In each node system, a request execution unit executes, for each state update request, state update processing of updating an object representing a state of a target specified in the request, and returns a response indicative of completion of the request without executing tamper-evidence processing. The tamper-evidence execution unit executes tamper-evidence processing of detecting whether one or more common completion requests of one or a plurality of update completion requests are tampered with by comparing updated objects of two or more node systems or summaries thereof. The update completion request is a state update request for which the execution of the state update processing has been completed. The common completion request is an update completion request that is common among two or more node systems of the plurality of node systems.
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