面向工程图版权保护和修改定位的半脆弱水印算法

A Semi-fragile Watermarking Algorithm for Copyright Protection and Tamper Localization of Engineering Graphics

针对现有的CAD工程图水印算法没有充分考虑工程图的图元特性,透明性低、鲁棒性差、修改定位不准确的问题,提出一种有效地应用于CAD工程图的半脆弱水印算法.首先将水印序列循环扩展,扩展后的长度等于工程图图元对的个数;然后遍历工程图图元对,在图元对的某属性比值中依次嵌入1位水印;水印提取是水印嵌入的逆过程,统计分析提取出的扩展水印序列可得正确的水印信息;最后采用对比提取出的扩展水印序列与理论嵌入值来验证图纸的完整性,并定位修改的部分.实验结果表明,该算法不仅能够免疫平移、旋转、缩放操作,还能抵抗修改、删除、增加图元等恶意攻击,同时能够实现精确的修改定位.

Current watermarking algorithms for CAD engineering graphics do not consider the characteristics of graphic primitives and the obvious disadvantage of these techniques is that they are severely weakened by low transparency,poor robustness and inaccurate tamper localization.This paper proposes an effective semi-fragile watermarking algorithm for CAD engineering graphics.Firstly,the watermark sequence is circularly extended.Then,the watermark is successively embedded into a scale factor of the adjacent graphic primitive.Watermark extraction is an inverse process of watermark embedding and the correct watermark information can be obtained from the extracted watermark sequence by statistical analysis.Comparing the extracted watermark sequence with the theoretical embedding values,the integrity of the graphics can be verified and the modified part can be located accurately.The experimental results show that the proposed algorithm can not only be immune to translation,rotation and scaling operations,but also resist modification,deletion and addition of primitives and other malicious attacks with high robustness,while tampering localization can be achieved precisely by using this algorithm.