Long PN Code Based DSSS Watermarking
Cyber crimes often involve complicated scenes. In this paper, the authors investigate unidentified crimes committed through anonymous communication networks. They developed a long Pseudo-Noise (PN) code based Direct Sequence Spread Spectrum (DSSS) flow marking technique for invisibly tracing suspect anonymous flows. By interfering with a sender's traffic and marginally varying its rate, an investigator can embed a secret spread spectrum signal into the sender's traffic. Each signal bit is modulated with a small segment of a long PN code. By tracing where the embedded signal goes, the investigator can trace the sender and receiver of the suspect flow despite the use of anonymous networks.