Patent ID: 8259949

Claim:
A method for protecting digital content, the method comprising: receiving, at a source device, a digital certificate from a presentation device; using public key infrastructure (PKI) to determine, at the source device, whether the presentation device has been authorized by a certificate authority (CA) to receive protected content; generating a session key and a master key at the source device; receiving a nonce from the presentation device; using the session key to encrypt data comprising video data that includes pixels within lines within frames; using the master key and the nonce from the presentation device to encrypt the session key; transmitting the encrypted session key to the presentation device before transmitting the encrypted data to the presentation device; and transmitting the encrypted data to the presentation device only if the source device determines that the presentation device has been authorized by the CA to receive protected content; wherein the operation of using the session key to encrypt data comprises: generating primary cipher data with a first cipher module, based at least in part on the session key; using at least first, second, third, and fourth cipher blocks in a second cipher module to generate four or more instances of secondary cipher data, based at least in part on the primary cipher data from the first cipher module; encrypting four or more different pixels in the video data with the secondary cipher data from four or more different secondary cipher blocks, respectively; and mixing bits in each secondary cipher block for multiple clock ticks between times that the secondary cipher data from that secondary cipher block is used to encrypt pixels.