| 摘要 |
<p>A server (20) is connectable to a client (30) and allows the client to acquire a message of an index designated by the client among N messages held by the server, where N is an integer of two or more. The server includes: a classification unit configured to classify the N messages into M classified messages by contents of the messages, so that redundant messages are removed; a message encryption unit configured to encrypt each of the M classified messages; a message provision unit configured to provide the M encrypted classified messages to the client; and a key sending unit configured to send the client, by oblivious transfer, a message key for decrypting the classified message corresponding to the message of the index designated by the client.</p> |
