Communication device, communication method, and recording medium

A communication method comprising:

• generating clock information representing timing by using a periodic clock signal;
• selecting at least a part of device information that is information commonly stored in one or more communication devices in accordance with the clock information;
• generating selection information that is different information for each piece of the clock information from at least a part of the device information selected;
• generating an encryption key by using at least the clock information and the selection information generated;
• executing at least one of encryption processing and decryption processing on communication data by using the encryption key generated;
• transmitting and receiving the communication data with the another communication device, when not correctly decrypting the communication data received from another communication device,
• generating one or more pieces of first estimated clock information that is the clock information different from the clock information in the own device at the time when the communication data is received,
• selecting at least a part of the device information according to the first estimated clock information, generating the selection information from at least the selected part of the device information,
• generating a first estimated encryption key by using at least the first estimated clock information and the selection information, and
• estimating the clock information generated by the another communication device according to a result of determining whether or not the communication data received from the communication device is correctly decrypted by using the generated first estimated encryption key.

A non-transitory computer-readable recording medium embodying a program for, the program causing a computer to perform a method, the method comprising:

• generating clock information representing timing by using a periodic clock signal;
• selecting at least a part of the device information that is information commonly stored in one or more communication devices in accordance with the clock information;
• generating selection information that is different information for each piece of the clock information from at least part of the device information selected;
• generating an encryption key by using at least the clock information and the selection information generated;
• and
• executing at least one of encryption processing and decryption processing on communication data by using the encryption key generated;
• transmitting and receiving the communication data with the another communication device, when not correctly decrypting the communication data received from another communication device,
• generating one or more pieces of first estimated clock information that is the clock information different from the clock information in the own device at the time when the communication data is received,
• selecting at least a part of the device information according to the first estimated clock information, generating the selection information from at least the selected part of the device information,
• generating a first estimated encryption key by using at least the first estimated clock information and the selection information, and
• estimating the clock information generated by the another communication device according to a result of determining whether or not the communication data received from the communication device is correctly decrypted by using the generated first estimated encryption key.