Method and System for Data-Hiding Within Audio Transmissions

Abstract

A method for hiding data within cover audio uses a set of sample codebook waveforms that are each assigned a unique representative digit value. A hidden data sequence representing the data is formed from the waveforms by concatenation of the waveforms assigned to the digit values of the data. The sequence is superimposed upon segments of the cover audio at a fractional amplitude. After transmission, the received signal is decompressed if necessary, the hidden data sequence is recovered from the cover audio, and the data is recovered from the hidden data sequence. This may be done by recovering the locations of the codebook waveforms and interpolating the time markers of the locations. The recovered data may be cleaned up by using estimated distances between successive cross-correlations to discard extraneous correlation peaks and sequence recurrence to probabilistically delete overlapping correlation peaks.

What is claimed is: 
     
         1 . A method for hiding data within cover audio, comprising the steps of:
 choosing a set of sample codebook waveforms;   assigning a unique representative digit value to each codebook waveform in the set;   based on the codebook waveform representative digit values, forming, from the codebook waveforms, a hidden data sequence representing the data; and   repeatedly superimposing the hidden data sequence upon segments of cover audio at a fraction of the amplitude of the cover audio.   
     
     
         2 . The method of  claim 1 , further comprising the steps of:
 transmitting the cover audio with superimposed hidden data sequence;   receiving the transmitted cover audio with superimposed hidden data sequence;   recovering the hidden data sequence from the received cover audio with superimposed hidden data sequence; and   recovering the data from the hidden data sequence.   
     
     
         3 . The method of  claim 2 , wherein the step of recovering further comprises:
 recovering the locations of the codebook waveforms; and   interpolating the time markers of the locations to determine the transmitted data sequence.   
     
     
         4 . The method of  claim 3 , wherein the locations of the codebook waveforms are recovered by matched filtering. 
     
     
         5 . The method of  claim 2 , further comprising the step of cleaning up the recovered data by using estimated distances between successive cross-correlations to discard extraneous correlation peaks and sequence recurrence to probabilistically delete overlapping correlation peaks. 
     
     
         6 . The method of  claim 1 , further comprising the steps of:
 repeatedly segmenting the cover audio to match the size of the hidden data sequence for the step of superimposing; and   reconstructing the cover audio as a continuous stream prior to transmission.   
     
     
         7 . The method of  claim 1 , wherein each codebook waveform in the set is a short spoken word. 
     
     
         8 . The method of  claim 1 , wherein the hidden data sequence is formed by concatenation of the codebook waveforms for the representative digit values of the data. 
     
     
         9 . The method of  claim 2 , further comprising the steps of:
 compressing the cover audio with superimposed hidden data sequence prior to the step of transmitting; and   decompressing the received compressed cover audio with superimposed hidden data sequence prior to the step of recovering.   
     
     
         10 . A system for sending hidden data within cover audio, comprising:
 a codebook waveform selection application configured to select a set of codebook waveforms and assign a representative data value to each codebook waveform;   a hidden data sequence generator configured to form a hidden data sequence by concatenating codebook waveforms according to their associated representative data value to represent the data to be hidden;   a cover audio with superimposed hidden data sequence signal generator configured to repeatedly superimpose the hidden data sequence upon segments of cover audio at a fraction of the amplitude of the cover audio; and   a hidden data recovery application configured to recover the hidden data sequence from the cover audio with superimposed hidden data sequence and to recover the data to be hidden from the hidden data sequence.   
     
     
         11 . The system of  claim 10 , further comprising:
 a transmitter configured for transmitting the cover audio with superimposed hidden data sequence; and   a receiver configured for receiving the transmitted cover audio with superimposed hidden data sequence.   
     
     
         12 . The system of  claim 10 , wherein the hidden data recovery application is further configured to recover the locations of the codebook waveforms and interpolate the time markers of the locations to determine the transmitted hidden data sequence. 
     
     
         13 . The system of  claim 12 , wherein the hidden data recovery application is configured to recover the locations of the codebook waveforms by matched filtering. 
     
     
         14 . The system of  claim 12 , wherein the hidden data recovery application is further configured to clean up the recovered data by using estimated distances between successive cross-correlations to discard extraneous correlation peaks and sequence recurrence to probabilistically delete overlapping correlation peaks. 
     
     
         15 . The method of  claim 10 , wherein the cover audio with superimposed hidden data sequence signal generator is further configured to repeatedly segment the cover audio to match the size of the hidden data sequence for the step of superimposing and to reconstruct the cover audio as a continuous stream prior to transmission. 
     
     
         16 . The system of  claim 10 , wherein each codebook waveform in the set is a short spoken word. 
     
     
         17 . The system of  claim 10 , further comprising applications configured for compressing the cover audio with superimposed hidden data sequence prior to transmission and decompressing the received compressed cover audio with superimposed hidden data sequence prior to recovery of the hidden data sequence.