A partial dual encryption encoder, consistent with certain embodiments of
the present invention receives video from a source of an unencrypted
digital video signal. A first segment of the unencrypted digital video
signal is selected for transmission over a first channel. A first
encrypter encrypts a second segment of the unencrypted digital video
signal under a first encryption method to produce a first encrypted
segment and a second encrypter that encrypts the second segment of the
unencrypted digital video signal under a second encryption to produce a
second encrypted segment. A multiplexer combines the unencrypted digital
video signal with the first and second encrypted segments for
transmission, so that the first segment is transmitted over a first
channel, the first encrypted segment is transmitted over the first
channel and the second encrypted segment is transmitted over a second
channel. A trigger message generator generates a trigger message
indicating that the second encrypted segment of the digital video signal
will be encrypted and will be transmitted on a second channel. The
multiplexer further combines the trigger message with the first segment,
the first encrypted segment and second encrypted segment.