Encrypted communication device, encrypted communication system, encrypted communication method, and program

An encrypted communication system in which a plurality of encrypted communication devices transmit and receive encrypted data, wherein

• each encrypted communication device includes
• a key storage that stores at least one common key which is shared with another encrypted communication device, and
• processing circuitry configured to:
• receive a notification indicating the completion of a key exchange;
• select an encryption key from the at least one common key stored in the key storage regardless of receiving the notification;
• generate the encrypted data by encrypting, by using the encryption key, data to be transmitted to the other encrypted communication device;
• transmit, to the other encrypted communication device, the encrypted data with a key index, by which the encryption key is uniquely identified, added thereto;
• receive the encrypted data with the key index added thereto from the other encrypted communication device;
• obtain, from the at least one common key stored in the key storage, a decryption key corresponding to the key index added to the encrypted data;
• and
• decrypt the encrypted data by using the decryption key.

An encrypted communication method by which a first encrypted communication device and a second encrypted communication device transmit and receive encrypted data, wherein

• the first encrypted communication device stores at least one common key, which is shared with the second encrypted communication device, in a first key storage,
• the encrypted communication method comprising:
• storing, by the second encrypted communication device, the at least one common key, which is shared with the first encrypted communication device, in a second key storage;
• receiving, by the first encrypted communication device, a notification indicating the completion of a key exchange;
• selecting, by the first encrypted communication device, an encryption key from the at least one common key stored in the first key storage regardless of receiving the notification;
• generating, by the first encrypted communication device, the encrypted data by encrypting, by using the encryption key, data to be transmitted to the second encrypted communication device;
• transmitting, by the first encrypted communication device, to the second encrypted communication device, the encrypted data with a key index, by which the encryption key is uniquely identified, added thereto;
• receiving, by the second encrypted communication device, the encrypted data with the key index added thereto from the first encrypted communication device;
• obtaining, by the second encrypted communication device, from the at least one common key stored in the second key storage, a decryption key corresponding to the key index added to the encrypted data;
• and
• decrypting by the second encrypted communication device, the encrypted data by using the decryption key.