1、1,Audio Steganography Echo Data Hiding,Jeff England EE 6886,2,Steganography vs. Watermarking,Both hide information discretely but for different purposes. Steganography Hiding data secretly for communication with another party. Ranging from small to large amount of data Non Detection most important W
2、atermarking Hiding a trademark or identification for the use of determining ownership. Usually Small amount of data Non Removal most important,3,Types of Steganography,Images LSB DCT encoding LSB of MS Byte Spread Spectrum Audio LSB (added noise can be heard) Phase Coding Spread Spectrum Tone Insert
3、ion Echo Data Hiding,4,Echo Data Hiding,Echo introduced to hide data into audio signal Echo is varied with three parameters:Initial AmplitudeDecay RateOffset,5,Inaudible echo,If the offset or delay is short then the echo produced will be unperceivable.Depends on the quality of recording but max dela
4、y without effect is noted to be around 1 ms. Also, initial amplitude and decay rate can also be set below the audible threshold of the human ear.,6,Encoding,The audio signal is divided into multiple windows. Two delay times are used to encode the hidden data. Binary 0 encoded with delay = offset Bin
5、ary 1 encoded with delay = offset + delta.,7,FIR Filter,A simple FIR Filter equation is used to delay the audio signal.H(z) = 1 +g*z d g = initial amplitude d = delayTherefore two impulses are used; one to copy the original signal and one to introduce an echo.,8,Final Encoding Step,Filter original s
6、ignal separately through both binary “one” and “zero” filter. Use mixer signal that contains a ramping function to switch between 0 and 1 encodings.,9,Decoding,Decoding is done by finding the delay before the echo.First find the Cepstrum of the encoded signal. Finding the Cepstrum makes the echo del
7、ay more pronounced and easier to detect.F-1(ln(F(x)2)Then find the autocorrelation of the Cepstrum signal.,10,Result of Auto-Correlation of Cepstrum,11,Goals,Implement Echo hiding Algorithm Determine the thresholds of when the echo becomes perceivable Type of music Amount of Delay (determines the am
8、ount of data that can be embedded) Determine if algorithm is easily detectable, via use of spectrograms or other means Determine if mp3 compression destroys the hidden data,12,References,W. Bender, D. Gruhl, N. Morimoto, A. Lu, “Techniques for data hiding,” http:/ 1996. Kaliappan Gopalan and Stanley
9、 Wenndt,“Audio Steganography for covert data transmission by imperceptible tone insertion”, www.calumet.purdue.edu/engr/docs/GopalanKali_422_049.pdf Ingemar J. Cox, Joe Kilian, F. Thomson Leighton, and Talal Shamoon, “Secure Spread Spectrum”, IEEE Transactions on Image Processing, Vol. 6, No. 12, December 1997,
