Variable starting state scrambling circuit

DETAILED DESCRIPTION It is an object of this invention to provide a scrambling/descrambling technique which is relatively secure even from an unauthorized user having the same receiver hardware.
Briefly, the present invention comprises a method and apparatus by which the PN sequence generators in the transmitter and receiver are periodically set to identical but variable starting states.
A starting state value to be used at the transmitter as an initial scrambling sequence value is transmitted over a privacy channel to the receiver so that the receiver knows the same starting state used at the transmitter.
In a preferred embodiment of the invention, the transmitter and receiver each include multibit storage registers for storing a particular such value.
The contents of this register can be periodically changed, and setting of the PN sequence generators at the scrambler and descrambler is performed by loading the stored initial scrambling sequence value into the PN sequence generator in response to a start, or load, pulse which can be generated and transmitted in a conventional manner.
The initial scrambling sequence value, which is generated at the transmitter, can be transmitted to the receiver over a privacy channel and can be preferably encrypted in accordance with the well known DES.