为了使数字水印算法具有更好的鲁棒性，首先阐述了迭代函数系（iterated function system，IFS）理论，并给出了构造IFS吸引子的随机迭代算法；然后从理论分析了IFS吸引子抗几何失真的特性，并提出了一种非对称数字水印算法；接着利用三点法将数字水印信息转化为IFS码，并由重构的分形水印图像与原始图像进行相关性处理得到索引集；最后版权者和第3信任方用私钥将索引集进行数字签名和加盖时间戳。水印检测时，只需利用第3信任方和版权者的公钥，而不需要原始图像参与。实验结果表明，该算法对噪声、滤波、压缩

In this paper，in order to obtain more robust digital watermark scheme，firstly the theory of iterated function system（IFS）and the stochastic algorithm by which IFS attractor is constructed are proposed Secondly，by analyzing the robust character against geometric distortion of IFS attractor theoretically，a new scheme is provided，which is a asymmetric digital watermark one Thirdly，using tri point method，the paper translates the information of digital watermarking into IFS code，and the indices set can be attained by reconstructing the image of fractal watermarking and manipulating the original image relatively Finally the index set is signed and time stamped by the owner and trusted third partys private keys Using the owner and trusted third partys private keys，the watermark can be detected without the original image The experimental results show that the watermark scheme is robust against image manipulations，such as noise adding，filtering，compression and rotation