Communication system, node device, communication terminal, key management method, and non-transitory computer-readable medium in which program is stored

A node device that carries out an authentication process on each of a plurality of communication terminals that form a communication group, the node device comprising:

• a deriving unit configured to derive first keys unique to the respective communication terminals by using information shared between the node device and each of the communication terminals through the authentication process and derive a second key common to the communication group;
• a calculating unit configured to calculate an exclusive OR of between each of the first keys and the second key;
• and
• a transmitting unit configured to transmit the respective XOR values obtained by the calculating unit to the respective communication terminals.

A communication terminal that forms a communication group together with another communication terminal, the communication terminal comprising:

• a deriving unit configured to derive a first key unique to the own communication terminal by using information shared between the communication terminal and a node device through an authentication process on the own communication terminal;
• a receiving unit configured to receive an XOR value from the node device;
• and
• a reproducing unit configured to reproduce a second key common to the communication group by calculating an exclusive OR between the first key and the XOR value,
• wherein the XOR value is obtained by the node device calculating an exclusive OR between the first key and the second key.

A key management method executed in a node device that carries out an authentication process on each of a plurality of communication terminals that form a communication group, the key management method comprising:

• deriving first keys unique to the respective communication terminals by using information shared between the node device and each of the communication terminals through the authentication process;
• deriving a second key common to the communication group;
• calculating an exclusive OR of between each of the first keys and the second key;
• and
• transmitting the respective XOR values obtained in the calculating to the respective communication terminals.

A key management method executed in a communication terminal that forms a communication group together with another communication terminal, the key management method comprising:

• deriving a first key unique to the communication terminal by using information shared between the communication terminal and a node device through an authentication process on the communication terminal;
• receiving an XOR value from the node device;
• and
• reproducing a second key common to the communication group by calculating an exclusive OR between the first key and the XOR value,
• wherein the XOR value is obtained by the node device calculating an exclusive OR between the first key and the second key.