Abstract: A key exchange technique of performing a key exchange among N (?2) parties, which can conceal metadata on communication, is provided. A key exchange method includes: a first key generation step in which a communication device Ui generates a first key; a first anonymous broadcast step in which the communication device Ui anonymously broadcasts the first key with a set R?{Ui} being designated for i?{1, . . . , n} and the communication device Ui anonymously broadcasts the first key with ? being designated for i?{n+1, . . . , N}; a second key generation step in which the communication device Ui generates a second key; a second anonymous broadcast step in which the communication device Ui anonymously broadcasts the second key with the set R?{Ui} being designated for i?{1, . . . , n} and the communication device Ui anonymously broadcasts the second key with ? being designated for i?{n+1, . . . , N}; and a session key generation step in which the communication device Ui generates a session key SK for i?{1, . . .

Abstract: The life of a sacrificial anode for use in a pump device, such as a seawater pump, is extended, thus extending the life of a corrosion protection system of the seawater pump device. A pump device includes corrosion system including: a measurement unit located at a portion of a column pipe to be immersed into seawater; and a temperature control device located at an installation site of the pump device. In this corrosion protection system, a sacrificial anode electrically conductive with the column pipe and capable of being controlled in temperature is attached through a heating/cooling unit and a thermal conduction sheet to the column pipe. The temperature control device is configured to control, based on the temperature of the sacrificial anode measured by the measurement unit, the temperature of the sacrificial anode using the heating/cooling unit attached through the thermal conduction sheet to the sacrificial anode.