Asymmetric schemes belong to second generation of watermarking. Whereas their need and advantage are well understood, many doubts have been raised about their robustness and security. Four different asymmetric schemes have been proposed up to now. Whereas they were seemingly relying on completely different concepts, they share the same performances. Exploring in detail these concepts, the authors propose a common formulation of the four different detector processes. This allows to stress common features about security of asymmetric schemes.