Scrambling a compression-coded signal

Abstract

This invention provides methods and apparatus for protecting data transmitted using standard compression techniques such as Huffman coding. After input data is preprocessed (filtered, quantized, etc.), the data is encoded using a Huffman coder based on Huffman codes or code books which have been scrambled to change the order of the code books and/or codes from established standard Huffman code books and/or codes. When the transmitted information is received by a Huffman code receiver, the received data may be decoded using the scrambled Huffman code book/codes to obtain the data that was transmitted by the transmitter.

1 . A method for protecting a data transmission comprising the steps of: 
 encoding a first portion of said data with a first standard code book,    encoding a second portion of said data either 
 (a) with a second standard code book that is different from said first code book but whose codes are also codes of said first code book, or  
 (b) by encoding the second portion with the first standard code book and scrambling the coded results in a predetermined manner; and  
   transmitting encoded data.    
   
   
       2 . The method of  claim 1 , wherein the scrambling step scrambles the standard codes so that a decoder corresponding to the first standard codes cannot successfully decode the encoded data.  
   
   
       3 . The method of  claim 1 , wherein the scrambling step is performed based on scrambling information, the scrambling information being transmitted with the encoded data.  
   
   
       4 . The method of  claim 1 , wherein the standard code books are Huffman code books.  
   
   
       5 - 8 . (canceled)  
   
   
       9 . The method of  claim 1 , wherein the transmitted data include in-stream data that indicates a change of code book or code scrambling.  
   
   
       10 . The method of  claim 1 , wherein the standard codes are Huffman code books.  
   
   
       11 . An apparatus that protects a data transmission using a plurality of standard code books where each of the code books encodes a preselected portion of the data, comprising: 
 an encoder responsive to said data that yields results that correspond to a first portion of the data being encoded with a preselected fixed code book and a second portion of the data being encoded with said preselected fixed code book that has its codes scrambled;    a transmitter that transmits encoded data.    
   
   
       12 . The apparatus of  claim 11 , wherein the encoder comprises an encoding unit coupled to a scrambling unit where the scrambling unit scrambles results of said encoding unit during said second portion of the data, where the scrambling replaces one code from the code book with another code from the code book.  
   
   
       13 . The apparatus of  claim 12 , wherein the scrambling unit scrambles based on scrambling information, the scrambling information being transmitted with the encoded data.  
   
   
       14 . The apparatus of  claim 11 , wherein the code book is a Huffman code book.  
   
   
       15 . The apparatus of  claim 13 , wherein the scrambling information is based on one or more of a fixed table or an algorithm.  
   
   
       16 . The apparatus of  claim 15 , wherein the algorithm is initialized with an initial value.  
   
   
       17 . The apparatus of  claim 16 , where in one or more of the fixed tables an identification of the algorithm or the initial value is either agreed upon between a transmitter and one or more intended receivers prior to transmission of the encoded data or transmitted with the encoded data.  
   
   
       18 . The apparatus of  claim 17 , where in one or more of the fixed tables the identification of the algorithm or the initial value is transmitted in encrypted form.  
   
   
       19 . The apparatus of  claim 17 , wherein the transmitted data include in-stream data that indicates a change of code book or code scrambling.  
   
   
       20 . The apparatus of  claim 11 , wherein the standard codes are Huffman code books.  
   
   
       21 . The method of  claim 1  where the data represents video and audio information, and the first portion is a portion of said video and/or audio that is desired to be decoded with said first code book.  
   
   
       22 . The method of  claim 21  where said first portion is selected based on content of said data transmission.  
   
   
       23 . The method of  claim 21  where said first portion is distributed in time.  
   
   
       24 . The method of  claim 21  where said first portion is selected so that information in selected frequency bands can be recovered with decoding in accord with the first code book, and not recovered in other frequency bands with decoding in accord with the first code book.  
   
   
       25 . The method of  claim 1  where said data transmission is divided into sub-streams, some sub-streams belong to the first portion and other sub-streams belong to the second portion.  
   
   
       26 . The method of  claim 25  where information in said data transmission is divided into said sub-streams based on type of information, frequency band of said information, and/or time intervals.