Patent ID: 7106861

Claim:
A digital AV data transmitting unit comprising: data significance deciding means deciding the significance degree of digital AV data; transmitting-side plurality-of-authentication-rules storing means storing a plurality of types of authentication rules; transmitting-side authentication selecting means selecting one type of rule from the transmitting-side plurality-of-authentication-rules storing means in accordance with a decision result by the data significance deciding means when receiving an authentication request; and transmitting-side authenticating means performing authentication in accordance with the selected authentication rule; wherein the plurality of types of authentication rules Includes a first rule configured to use a public key and a secret key to provide a first type of encryption having high-security against forgery or alteration, and a second rule configured to use a common key to provide a second type of encryption having low-security against forgery or alteration, and the public and secret keys, or the common key are used for transmitting a sole single key from a transmission unit to a plurality of receiving units depending on a significance degree of the digital AV data, and the sole single key does not depend on the respective receiving units, and is used when the digital AV data is transmitted from the transmitting unit to the receiving units, and if the first rule or the second rule Is selected by the transmitting-side authenticating means, the digital AV data encrypted using the transmitted sole single key is transmitted from the transmitting unit to the receiving units.