A system and method for cryptographically securing a graphics system connectable via an external bus to a computing system, the graphics system including a graphics processor, a video memory and a memory controller for controlling the flow of data to and from the video memory. The graphics system further includes a copy engine for copying data between a system memory of the computing system and the video memory, where this copy engine acts independently of the graphics processor of the graphics system. The present invention enables the copy engine of the graphics system to decrypt encrypted data in the course of copying data from the system memory to the video memory and to encrypt unencrypted data in the course of copying data from the video memory to the system memory. Thus, cryptographic protection of secure content may be assured by the graphics system without the excessive usage of its primary resources for this non-graphical purpose.