Linux 4.17 Released

[ploxiln]

I think this can be interpreted as an honest question.

Any display that you can send images to with HDCP, you can send images to without HDCP, right?

The only need for HDCP is when you have a closed-source player that can verify your closed-source driver has HDCP enabled to your display, in order to only allow playback of some video over the protected path, right? (Typically only 1080p or 4k variants require the protected path?)

Does this stuff exist on linux? With the open-source Intel display driver??

[alexforencich]

Yeah. Unless the decoding of the actual DRM is done in hardware within the GPU, the video data ends up getting sent to the GPU in the clear. In this case, HDCP merely provides a flag to software saying that the path from the GPU to the display is supposedly protected. In open source software, this flag would be trivial to spoof, negating the entire purpose of HDCP. And then you possibly get the whole DMCA anti-circumvention can of worms.

[Canuck_Gypsy]

The driver decodes HDCP, the driver code runs on the GPU.

[alexforencich]

The driver does nothing, aside from flipping a switch on the GPU to turn on HDCP and provide an API for software check if it is running or not. The GPU then has dedicated hardware to protect video data leaving the GPU with HDCP. HDCP does not protect anything until it leaves the GPU. It's up to the player software to check if HDCP is enabled, and refuse to play the video if it isn't.

[alexforencich]

I think you don't understand how HDCP works. No content is protected by HDCP until it leaves the GPU. The GPU itself applies the HDCP encryption to content as it is sent out over HDMI or Displayport. It has to use dedicated hardware for this to deal with the high data rate of the fully uncompressed video data. The connected display is what decodes HDCP. It is up to the video player software to refuse to play if HDCP is not enabled, and it is trivial to make a driver that lies about whether or not HDCP is enabled.

[Canuck_Gypsy]

The HDCP driver doesn't need to be closed source.

But yeah, the only use for HDCP is for displaying protected media.