Data transmitting method and apparatus, and data communication method and apparatus

A data transmitting apparatus comprising:

• inquiring means for making an inquiry to a receiving apparatus when a count value is invalid, receiving a first random number generated in the receiving apparatus, and storing a count value n that is first generated from the first random number into a volatile memory;
• encrypting means for encrypting data to be transmitted by the count value n;
• transmitting means for transmitting data in a frame format including the count value n and the encrypted data;
• and
• count value changing means for changing the count value stored in the volatile memory, every time data is transmitted,
• wherein when the changed value exceeds a set range, an inquiry is made to the receiving apparatus, a second random number different from the first random number generated in the receiving apparatus is received, and a count value n′ (≠n) that is first generated from the second random number is stored into the volatile memory, and
• an encrypting process by the encrypting means, a transmitting process by the transmitting means, and a count value changing process by the count value changing means are repeated by using the count value n′.

A data communication method which performs communication via a radio channel capable of two-way communication between a transmitting apparatus and a receiving apparatus, wherein:

• a data transmitting method includes
• an inquiring step of making an inquiry to the receiving apparatus when a count value is invalid, receiving a first random number generated in the receiving apparatus, and storing a count value n that is first generated from the first random number into a volatile memory,
• an encrypting step of encrypting data to be transmitted by the count value n,
• a transmitting step of transmitting data in a frame format including the count value n and the encrypted data, and
• a count value changing step of changing the count value stored in the volatile memory, every time data is transmitted,
• in which when the changed value exceeds a set range, an inquiry is made to the receiving apparatus, a second random number different from the first random number generated in the receiving apparatus is received, and a count value n′ (≠n) that is first generated from the second random number is stored into the volatile memory, and
• the encrypting step, the transmitting step, and the count value changing step are repeated by using the count value n′;
• and
• a data receiving method includes
• an inquiry response step of receiving the inquiry, and transmitting the first random number to the receiving apparatus,
• a receiving step of receiving the data in the frame format transmitted in the transmitting step,
• a determining step of determining whether or not the count value received has increased or decreased from a value being held, and falls within the set range,
• a decrypting step of
• generating a decryption key by using the received count value when it is determined in the determining step that the received count value matches the count value being held, and decrypting encrypted data within a received frame with the generated decryption key, and
• discarding the received frame when it is determined that the received count value does not match the count value being held, and
• a count value changing step of changing the value being held, when the encrypted data within the frame is decrypted.

A data communication apparatus which performs communication via a radio channel capable of two-way communication between a transmitting apparatus and a receiving apparatus, wherein:

• a data transmitting apparatus includes
• inquiring means for making an inquiry to the receiving apparatus when a count value is invalid, receiving a first random number generated in the receiving apparatus, and storing a count value n that is first generated from the first random number into a volatile memory;
• encrypting means for encrypting data to be transmitted by the count value n;
• transmitting means for transmitting data in a frame format including the count value n and the encrypted data;
• and
• count value changing means for changing the count value stored in the volatile memory, every time data is transmitted,
• in which when the changed value exceeds a set range, an inquiry is made to the receiving apparatus, a second random number different from the first random number generated in the receiving apparatus is received, and a count value n′ (≠n) that is first generated from the second random number is stored into the volatile memory, and
• an encrypting process by the encrypting means, a transmitting process by the transmitting means, and a count value changing process by the count value changing means are repeated by using the count value n′;
• and
• a data receiving apparatus includes
• inquiry response means for receiving the inquiry, and transmitting the first random number to the receiving apparatus,
• receiving means for receiving the data in the frame format transmitted by the transmitting means,
• determining means for determining whether or not the count value received has increased or decreased from a value being held, and falls within the set range,
• decrypting means for
• generating a decryption key by using the received count value when it is determined by the determining means that the received count value matches the count value being held, and decrypting encrypted data within a received frame with the generated decryption key, and
• discarding the received frame when it is determined that the received count value does not match the count value being held, and
• count value changing means for changing the value being held, when the encrypted data within the frame is decrypted.