Patent ID: 7251833

Claim:
A method for enforcing restricted access of a media file, comprising: storing a media file; partitioning the media file into a plurality of sequential data blocks; generating a plurality of cryptographic token keys; encrypting the plurality of sequential data blocks with the plurality of cryptographic token keys, thereby producing a plurality of encrypted sequential data blocks; transferring at least a subset of the plurality of encrypted sequential data blocks from a sending server to a receiving client; selecting, by the sending server, a subset of the plurality of cryptographic token keys for transfer to the receiving client, wherein the subset of the plurality of cryptographic token keys enables decryption of one of more corresponding encrypted sequential data blocks of the transferred subset of the plurality of encrypted sequential data blocks, thereby enabling the receiving client to access only a selected portion of the media file as defined by the sending server, in accordance with an access status of the receiving client, and wherein the subset of the plurality of cryptographic token keys comprises fewer cryptographic token keys than the plurality of cryptographic token keys; and transferring the subset of the plurality of cryptographic token keys from the sending server to the receiving client, wherein non-selected cryptographic token keys are not transferred to the receiving client as defined by the sending server, in accordance with the access status of the receiving client.