Method and apparatus for detection of loss of cipher synchronization

A method for of detecting loss of stream cipher synchronization between a transmitter and a receiver in a video processing system, the method comprising:

• receiving, by the receiver, an encrypted video frame from the transmitter;
• obtaining an encrypted value for a selected pixel in the encrypted video frame;
• decrypting the encrypted pixel value using a current key stream of the receiver;
• re-encrypting the pixel value;
• and
• sending the re-encrypted pixel value from the receiver to the transmitter, to enable the transmitter to detect loss of stream cipher synchronization, based at least in part on the re-encrypted pixel value from the receiver.

An apparatus for a video processing system, the apparatus comprising:

• a transmitter adapted to perform operations comprising:
• transmitting an encrypted video frame to a receiver;
• after transmitting the encrypted video frame to the receiver, receiving a re-encrypted pixel value from the receiver;
• obtaining a plaintext value for a selected pixel from an original video frame, wherein the original video frame corresponds to the encrypted video frame, and wherein the selected pixel corresponds to the re-encrypted pixel value received from the receiver;
• encrypting the plaintext value for the selected pixel into a new encrypted value;
• and
• detecting loss of stream cipher synchronization with the receiver, based at least in part on (a) the re-encrypted pixel value received from the receiver and (b) the new encrypted value.