A video source device includes a cipher unit. The cipher unit includes a block
cipher and a stream cipher. The video source device uses the block cipher to generate
at least one cipher key for use by the stream cipher to generate cipher bits for
ciphering video to be transmitted to a video recording device. The video source
device further provides n bits of copy control information to the video recording
device. The video source device incorporates the n-bit copy control information
as part of an initialization value, and initializes a register of a round function
of the block cipher with the initialization value. The video recording device also
includes a cipher unit of like kind, and operates the block and stream ciphers
in like manner to decipher the ciphered video received from the video source device.
Upon receiving the n-bit copy control information, the video recording device also
forms an initialization value and initializes a corresponding register of the corresponding
round function of its block cipher. Accordingly, protection is provided to the
copy control information.