Sensor network, sensor management server, key updating method and key updating program

A sensor management server connected mutually with a large number of sensor terminals each storing an element key, which transmits a key update message for updating the element key to each of the sensor terminals and performs encrypted communication with each of the sensor terminals by utilizing the element key, the sensor management server comprising:

• a key delivery module which transmits the key update message to each of the sensor terminals;
• a communication volume detection module which detects a communication volume when transmitting or retransmitting the key update message, and
• a multiplicity determination module which specifies a numerical value of the multiplicity that is a lower limit value of number of the key update messages transmitted to each of the sensor terminals according to the detected communication volume, wherein
• the multiplicity determination module successively specifies the multiplicity with which the communication volume when transmitting or retransmitting the key update message becomes a minimum value, and the key delivery module successively transmits the key update message according to the specified multiplicity.

A key updating method used in a sensor network comprising a large number of sensor terminals each storing an element key and a sensor management server connected mutually, in which the sensor management server transmits a key update message to each of the sensor terminals, and each of the sensor terminals updates the element key according to the received key update message and performs encrypted communication with the sensor management server by utilizing the element key, wherein:

• a multiplicity determination module of the sensor management server initially sets a numerical value of a multiplicity that is lower limit value of number of the key update messages transmitted to each of the sensor terminals;
• a key delivery module of the sensor management server transmits the key update message according to the set numerical value of the multiplicity;
• a communication volume detection module of the sensor management server detects a communication volume when transmitting or retransmitting the key update message;
• and
• the multiplicity determination module of the sensor management server specifies the numerical value of the multiplicity when transmitting the key update message next time according to the detected communication volume.

A non-transitory computer readable recording medium storing a key updating program used in a sensor network comprising a large number of sensor terminals each storing an element key and a sensor management server connected mutually, in which the sensor management server transmits a key update message to each of the sensor terminals, and each of the sensor terminals updates the element key according to the received key update message and performs encrypted communication with the sensor management server by utilizing the element key, the program causing a computer provided to the sensor management server to execute:

• a procedure for initially setting a numerical value of a multiplicity that is a lower limit value of number of the key update messages transmitted to each of the sensor terminals;
• a procedure for transmitting the key update message according to the set numerical value of the multiplicity;
• a procedure for detecting a communication volume when transmitting or retransmitting the key update message;
• and
• a procedure for specifying the numerical value of the multiplicity when transmitting the key update message next time according to the detected communication volume.

A sensor management server connected mutually with a large number of sensor terminals each storing an element key, which transmits a key update message for updating the element key to each of the sensor terminals and performs encrypted communication with each of the sensor terminals by utilizing the element key, the sensor management server comprising:

• key delivery means for transmitting the key update message to each of the sensor terminals;
• communication volume detection means for detecting a communication volume when transmitting or retransmitting the key update message, and
• multiplicity determination means for specifying a numerical value of the multiplicity that is a lower limit value of number of the key update messages transmitted to each of the sensor terminals according to the detected communication volume, wherein
• the multiplicity determination means successively specifies the multiplicity with which the communication volume when transmitting or retransmitting the key update message becomes a minimum value, and the key delivery means successively transmits the key update message according to the specified multiplicity.