Let me start out by mentioned that I am by no means a security expert -- in the late 1990s I simply structured the DVD CSS key transfer interfaces for Linux and then got them integrated into the Linux kernel as the "DVD ioctls," primarily intended for players (such as the Creative Labs Encore/Dxr2 Auravision VxP524 hardware driver (and here) I had started working on in early 1998). Hardware playback devices, such as the [old] VxP524, do not descramble over the CPU bus. However the interfaces I created to support encrypted transfer could be used for both hardware and software players.