the present invention provides for hdcp over usb using a virtualizing usb controller that provides a physical usb controller for external communications and a virtual usb controller for communicating with an incorporating host . when the host inquiries whether hdcp is supported , the virtual usb controller responds that it is supported . when a video data is received from the host , an hdcp module on the virtualizing usb controller encrypts the video . the virtualizing usb controller then transmits the encrypted video data out the physical usb port . the virtualizing controller can be used in connection with a usb display with a usb controller that supports hdcp decryption . as a result , hdcp video can be transmitted over a usb cable for display . as shown in fig1 , a computer system api includes a host computer 11 and a display 13 connected to each other by a usb cable 14 . display 13 includes a display panel 15 , a stand 17 , and a base 19 . base 19 contains a usb controller 21 that supports decryption for hdcp protected video so that hdcp video can be displayed . host computer 11 runs a multimedia application 23 on an operating system 25 . operating system 25 includes a video driver 27 that queries a video controller regarding capabilities before transmitting video data . in the case multimedia application 23 is playing hdcp protected content , e . g ., playing an hdcp protected blu - ray disk , video driver 27 queries whether a video controller supports hdcp encryption . if the controller supports hdcp encryption , video driver 27 provides high - definition video ; otherwise , lower - resolution video data is provided that can be sent without protection ( which is what would be sent over a conventional usb controller ). host computer 11 uses a virtualizing usb controller 30 to support the hdcp - over - usb capabilities of display 13 . video driver 27 communicates with controller 30 over a pci system bus 50 , which carries video data 51 as well as control signals and data 53 . controller 30 includes a physical usb controller 31 , a processor 33 , and computer - readable media 35 . media 35 is encoded with a virtual usb controller 40 , which includes a video driver 41 for physical usb controller 31 , an hdcp module 43 , which in turn provides an “ information constraint token ” flag 45 . video driver 41 provides video data 47 and control signals and data 49 compatible with physical usb controller 41 . virtualizing usb controller 30 supports a method me 1 , flow charted in fig1 . at method segment m 1 , virtual controller 40 receives an inquiry from video driver 27 regarding the capabilities of virtual controller 40 . based on the set status of ict flag 45 , controller 40 returns an indication that hdcp is supported at method segment m 2 . virtual controller 40 receives video data from multimedia application 23 at method segment m 3 , which it attempts to transmit . at method segment m 4 , hdcp module 43 applies hdcp encryption to the video data to yield encrypted video data . if there is no inquiry at method segment m 1 , hdcp module 43 leaves the video data unencrypted . at method segment m 5 , video driver 41 transmits the encrypted video data via physical ubs controller 31 . at method segment m 6 , display usb controller receives and decrypts the video data . at method segment m 7 , display 13 presents decrypted video at panel 15 . if physical controller 31 had been directly coupled to system bus 50 , it would have responded to the inquiry of method segment m 1 that it did not support hdcp . in that case , the video signal at 51 would have been relatively low - resolution ( non - hd ) data , which would have been transmitted unencrypted to display 13 . when video driver 41 inquires about hdcp capability , physical usb controller 31 will not indicate that hdcp is supported . of course , since hdcp module 43 has encrypted the video it has received , the video can be transmitted by physical controller 31 without further encryption and still be hdcp compliant . physical usb controller 31 supports a second channel to which a usb cable 61 is connected . in this case , the destination is a usb dock 63 , which converts the received encrypted hd video data for transmission over a “ digital video interface ” dvi cable 65 to a display 67 . in this case , display 67 does not have a usb connection or provide for hdcp over usb . thus , virtualizing usb controller 30 provides for hdcp on a non - usb display or a usb display that does not support hdcp over usb . in an alternative embodiment , a video driver of a virtualizing controller does not inquire regarding hdcp support . depending on the embodiment , a virtualization controller can support only one or , alternatively , one or more displays . also , the host computer may support another display through a dedicated video port . these and other variations upon and modifications to the illustrated embodiment are provided by the present invention , the scope of which is defined by the following claims .