Advanced colluder detection techniques for OSIFT-based hiding codes

In this work, we examine a family of anti-collusion codes using the principle of "orthogonal spreading followed by the inverse Fourier transform (OSIFT)" as introduced in (B.-H. Cha and C.-C. Jay Juo, 2007). The Hadamard-Walsh (HW) codes were adopted as the orthogonal spreading codes in (B.-H. Cha and C.-C. Jay Juo, 2007). Here, we introduce another type of orthogonal spreading codes; namely, the carrier interferometry (CI) codes, which are comparable to HW codes. To detect OSIFT hiding codes against weighted collusion attacks, we propose advanced detectors that can identify a large number of colluders with weighted collusion attacks. The proposed detection schemes include the maximal ratio combining (MRC) scheme for colluder detection in the same group and the multiuser detection (MUD) scheme for colluder detection in different groups. It is demonstrated that HW- and Cl-based OSIFT codes have robust performance with advanced detection schemes against weighted collusion attacks compared with conventional matched filter (MF) in an exemplary audio watermarking system.