Data management apparatus, power usage calculation system, and data management method

A power usage calculation system comprising:

• at least one power meter;
• a data management apparatus;
• an application server;
• and
• a key management server, wherein
• the at least one power meter includes
• a collector configured to collect a power usage amount for a unitary time;
• a first generator configured to generate a first value by encrypting the power usage amount using a first secret key shared with the key management server;
• and
• a first transmitter configured to transmit the first value to the data management apparatus,
• the data management apparatus includes
• a first receiver configured to receive the first values from the at least one power meter;
• a second generator configured to generate a second value by summing the first values;
• a second receiver configured to receive a conversion key from the key management server;
• a convertor configured to convert the second value into a third value by using the conversion key;
• and
• a second transmitter configured to transmit the third value to the application server,
• the application server includes
• a third receiver configured to receive the third value from the data management apparatus;
• a third generator configured to generate a fourth value by decrypting the third value using a second secret key shared with the key management server, the fourth value being a value acquired by summing power usage amounts collected by the at least one power meter;
• and
• an executor configured to execute a predetermined application using the fourth value, and
• the key management server includes
• a fourth generator configured to generate the conversion key using the first secret key and the second secret key in response to a request from the data management apparatus;
• and
• a third transmitter configured to transmit the conversion key to the data management apparatus.

A data management method, comprising:

• receiving a plurality of first values from at least one power meter collecting a power usage amount for a unitary time, each of the first values being the power usage amounts encrypted using a first secret key maintained by the power meter;
• generating a second value by summing the first values;
• receiving a conversion key from a key management server, the conversion key being generated by using the first secret key and a second secret key maintained by an application server that executes a predetermined application by using a value acquired by summing power usage amounts collected by the at least one power meter;
• converting the second value into a third value by using the conversion key;
• and
• transmitting the third value to the application server, wherein
• the third value is a value from which a value acquired by summing the power usage amounts is acquired by decrypting the third value using the second secret key by the application server.