HDCP is required for all equipment that uses a HDMI connection. Since HDCP is a proprietary technology, it requires a license to be implemented and as part of the license agreement, a manufacturer must agree to limit the capabilities of the other video outputs on a device. This means that in effect, a movie disc can instruct a source player to downgrade the video quality if a user attempts to transmit high definition video content through a connection that doesn't feature HDCP.
With the master key released, anyone can now create their own source/sink keys.
You can view the original post here: HDCP Master Key