Data transmitting/receiving method, data transmission apparatus, data reception apparatus, data transmission/reception system, av contents transmitting method, av contents receiving method, av contents transmission apparatus, av contents reception apparatus, and program recording medium

Abstract

A data transmitting and receiving method for improving transmission and reception efficiency can be obtained by improving the security through update of a control key and reduction of the frequency of the authentication and key exchange process. An STBtransmits encrypted digital data Kw (D) obtained by encrypting digital data D using a work key Kw, and an encrypted work key Kc (Kw) obtained by encrypting the Kw using a control key Kc. The Kc is periodically or non-periodically updated, and an identifier L identifying the Kc is assigned to each Kc. A VTR devicedecrypts the received Kc (Kw) using the Kc obtained by performing the authentication and key exchange process with the STB, decrypts the Kw (D) received using the Kw to obtain the D. It is determined whether or not the Kc has been updated while the reception process is suspended by referring to the transmitted L when the reception process is suspended and then resumed. If it is determined that the Kc has been updated, then the authentication and key exchange process is performed again to obtain the updated Kc.