Practical security of non-invertible watermarking schemes

Designing secure digital watermarking schemes resistant to invertibility attacks (or more generally, ambiguity attacks) has been challenging. In a recent work, Li and Chang (IHW'04) give the first stand-alone provably secure non-invertible spread-spectrum watermarking scheme based on cryptographically secure pseudo-random generators. Despite its provable security, there are certain constraints on the security parameters that require further analysis in practice, where it is more important to analyze the exact security instead of theoretical asymptotic bounds. In this paper, we consider a security notion that is slightly weaker theoretically but still reasonable in practice, and show that with this alternative security notion, the exact requirements on the parameters can be analyzed, and such analysis can be used to guide flexible implementations of similar schemes in practice.