A video source device includes a cipher unit. The video source device uses the
cipher unit to generate cipher bits for ciphering video to be transmitted to protect
the video from unauthorized copying. The video source device authenticates video
receiving devices using a symmetric ciphering/deciphering process that requires
the video source device to generate and provide the video receiving device with
a pseudo random number as the seed/basis number for the symmetric ciphering/deciphering
process. The video source device is further provided with a state machine that
controls the cipher unit to generate the required pseudo random number for the
video source devices, thereby eliminating the need of having to provide separate
circuitry to generate the required pseudo random numbers.