DATA TRANSMITTER AND DATA TRANSMISSION METHOD

摘要

PROBLEM TO BE SOLVED: To enhance the security against leakage of ciphered transmission data by improving the security of transmission of a ciphering key or a decoding key. SOLUTION: A large capacity transmission channel 12 such as a satellite transmission channel through which data of a large capacity are transmitted and a small capacity transmission channel 13 such as a public telephone line to send a ciphering key or a decoding key or information to generate the keys are provided. A ciphering session key is converted by using a work key and a destination address of a receiver 2 being a transmission destination. Furthermore, a decoding session key is converted by using its own address and the work key. The work key is preferably ciphered and sent through the small capacity transmission line 13. A transmitter 1 ciphers data 5 to be transmitted by using the converted ciphering session key 7 as above and adds transmission control information such as destination data to the data 5 and the resulting data 5 are sent to a receiver 2 through the large capacity transmission channel 12. The receiver 2 uses a decoding session key 8 converted as above to decode ciphered data 19.