System for detecting whether client state matches predetermined state

A client connectable to a server storing a set including a predetermined state, the client comprising:

• a state management unit for managing the successively transitioning state of the client;
• a client-side communication unit for communicating with the server using a privacy-preserving set-intersection protocol for detecting whether an element in a mutual set is a common element between mutual sets while preserving privacy;
• and
• a determining unit for determining whether the state of the client is included in the set stored by the set storage unit on the basis of ciphertext received from the server in accordance with the privacy-preserving set-intersection protocol.

An information processing method for a server connectable to a client able to manage successively transitioned-to states, the method comprising the steps of:

• storing a set including a predetermined state;
• communicating with the client using a privacy-preserving set-intersection protocol for detecting whether an element in a mutual set is a common element between mutual sets while preserving privacy;
• and
• determining whether the state of the client is included in the set stored by the set storage unit on the basis of ciphertext received in accordance with the privacy-preserving set-intersection protocol.