Patent ID: 7634171

Claim:
A personal video recorder system comprising: a general-purpose computer having a host processor and memory; and at least one video recorder card implemented in the general-purpose computer, the video recorder card in the computer being configured to tune a receiver using a tuner to a particular channel or a frequency carrying digitally streamed video content comprising of intra-frames (I-frames) and predictive frames (P-frames), receive and scramble for storage the video content and record the scrambled video content into the memory in a scrambled form that cannot be perceptibly displayed by the general-purpose computer to prevent unauthorized distribution of the video content, the video recorder card being further configured to perform steps comprising: retrieve and descramble the video content from the memory and output the descrambled video content for playback to a display separate from the general-purpose computer, wherein the video recorder card comprises: a key management processor to derive keys based on a secret value local to the video recorder card, but unknown to the general-purpose computer; a content scrambler to scramble the video content using the keys derived by the key management processor; a direct memory access (DMA) engine to direct storage of the scrambled content at specified addresses in the memory; and an address scrambler to scramble the specified addresses for storage on the memory; and store a playlist on the memory, wherein the playlist comprises a list of content stored on the memory and data for an electronic program guide comprising upcoming content to be broadcast at a later date, wherein the playlist is partially encrypted such that the list of content stored on the memory is encrypted and the data for the electronic program guide is not encrypted, wherein the content scrambler and the address scrambler are implemented as a single unit that employs a same encryption algorithm.