Key exchange system, qkd apparatus, hub apparatus, method, and program

A quantum key distribution (QKD) apparatus in a key exchange system including:

• a QKD network including a plurality of QKD apparatuses that performs exchange of a key by using a quantum key distribution protocol and a plurality of key management apparatuses that relays the key;
• and a plurality of hub apparatuses that performs encrypted communication by using the key received from the key management apparatuses, the QKD apparatus comprising:
• a processor;
• and
• a memory storing program instructions that cause the processor to,
• in a case where the key is transmitted to an unreliable key management apparatus among the plurality of key management apparatuses, use a secret key shared in advance with a hub apparatus that receives the key via the unreliable key management apparatus, and transmit the key subjected to an exclusive OR with the secret key to the unreliable key management apparatus.

A hub apparatus in a key exchange system including:

• a quantum key distribution (QKD) network including a plurality of QKD apparatuses that performs exchange of a key by using a quantum key distribution protocol and a plurality of key management apparatuses that relays the key;
• and a plurality of hub apparatuses that performs encrypted communication by using the key received from the key management apparatuses, the hub apparatus comprising:
• a processor;
• and
• a memory storing program instructions that cause the processor to,
• in a case where the key is received from an unreliable key management apparatus among the plurality of key management apparatuses, use a secret key shared in advance with a QKD apparatus that transmits the key to the unreliable key management apparatus, and calculate an exclusive OR of the secret key and the key.