| 摘要 |
PROBLEM TO BE SOLVED: To shorten the time for acquiring images or voices by shortening the time to be occupied for sending out a cryptographic key by sending out key correspondent data so as to correspond to not only a key at that time but also a key to be next used within a prescribed overlap period before the time of changing a key used in enciphered data. SOLUTION: In the Fig. B, sections Odd0, Even1, Odd1 and Even2 are respectively periods for sending out the key correspondent data of cryptographic keys Odd0, Even1, Odd1 and Even2. Preceding to a time Tx to change the cryptographic key used in the enciphered data by Δt1 (Ts), the next key correspondent data are sent out. This is for receiving data without interrupting them while considering the time for restoring the cryptographic key from the key correspondent data on the reception side. Besides, the key correspondent data of the cryptographic key just used or enciphering data at present as well are continuously sent out even after the transmission of the next key correspondent data is started. Thus, an overlap period 40 is provided. |
