Methods and apparatus for protecting copyrighted information, e.g., video
signals, from unauthorized copying. Analog red (R), green (G) and blue
(B) video signals are transmitted from a source device, e.g., a display
adapter, to a display device, e.g., a monitor, over corresponding analog
signal lines after the identify of the destination device is confirmed by
receipt of a certificate assigned to the destination device. A session
key, used for encrypting the analog signals, is generated and exchanged
between the source and destination devices after the identification of
the destination device is confirmed. The source and destination devices
each includes a pseudo-random number generator driven by the session key.
The lines that carry the R, G and B video signals are changed, e.g.,
swapped, on a periodic basis as a function of the output of the
pseudo-random number generator in the source device. The destination
device, which has an input to its pseudo-random number generator
synchronized with the random number generator of the source device,
decrypts the received video signals in a complimentary fashion to the
encryption. Encrypted digital information subject to copying constraints
may be supplied to a display adapter via an IEEE 1394 compliant bus.