Data Hiding within Audio Signals Matthew Wiedemer CSE691 November 20, 2001

Overview  Steganography systems and their goals  Audio stego systems  Autocorrelation modulation scheme

Stego Systems  Data hiding, covert communications  Evade detection Stego Object Transmission EmbeddorExtractor Cover Object Stego Key Embedded Data Stego Key Embedded Data

Basic Stego System Goals  Transparent  Robust Survive compression encoding/decoding Survive attack intended to remove/forge object  Simplicity of embeddor and extractor  High throughput  Low probability of false detection (if using watermarks)

Audio Stego Systems  Add small amount of distortion  Use audio masking: human ear can’t distinguish weak and strong signals at same time Direct sequence spread spectrum – uses audio masking, susceptible to time scale modification Tone insertion – easy to find through frequency analysis Echo insertion – complex extraction, low robustness LSB – low robustness Compression-based – only contains watermark when compressed

Autocorrelation Modulation Scheme  Attains goals of high robustness, high transparency  Complex  Highly configurable

Autocorrelation Modulation System Model Stego Object Transmission EmbeddorExtractor Cover Signal Stego Key Embedded Data Stego Key Embedded Data

Delay or Advance Variable Gain or Attenuation Filter Gain Calculator Cover Signal Filtered Cover Signal Embedded Data Stego Signal Stego Object Transmission EmbeddorExtractor Cover Signal Stego Key Embedded Data Stego Key Embedded Data Embeddor *multiple difference signal components may be used **stego key is set of coefficients, constants used in block equations

Stego Object Transmission EmbeddorExtractor Cover Signal Stego Key Embedded Data Stego Key Embedded Data System Model Continued

Extractor Short-Term Integrator Filter Normalization Filtered Signal Stego Signal Delay Short-Term Integrator |*|² Regenerator Embedded Data

Conclusion  Designing a robust, secure, transparent, lossless stego system is difficult and complex; requires significant signal processing  An ideal solution would satisfy the needs of the music industry  Autocorrelation modulation satisfies these requirements better than any other audio stego/watermarking system available today