key information management method, content transmission method, key information management appliance, license management appliance, content transmission system, and terminal appliance

摘要

The present invention aims to reliably prevent illegal use of content when the content is encrypted and transmitted with a cipher key. A content transmission method of the present invention includes: a basic key creating step of creating a basic key K1; a cipher key creating step of creating a cipher key Kn and also creating mutual cipher keys K2 through Kn-1; a first key encrypting step of encrypting the mutual cipher key K2 with the basic key K1, a second key encrypting step of encrypting the mutual cipher keys K3 through Kn-1 and the cipher key Kn by successively using the keys K2 through Kn-1; a content encrypting step of encrypting content C with the cipher key Kn; a first transmitting step of transmitting content Kn (C) and one part among key data K1 (K2), . . . , Kn-1 (Kn) to a terminal apparatus 2 through a broadcast wave; and a second transmitting step of transmitting another part among the key data K1 (K2), . . . , Kn-1 (Kn) to the terminal apparatus 2 through a communication network.