Abstract: Concerning of the issue that the present fragile authentication algorithm’s positioning is on a low accuracy and security condition，a complete fragile watermark algorithm which is based on the chaos has been put forward and has been used to certificate the integrity of the image content and locate the tampering. The algorithm uses the methods to separate the original image into blocks，then to calculate the high 6-bit gray-scale for the mean of each pixel in a block of image as the image characteristics watermark information. It also uses chaotic sequence to encrypt watermark information and determine the location of each embedded watermark bit，tampering with positioning accuracy for the 2×2 pixel image block. Experimental results show that the algorithm is simple，safe，and has a good practicality.

Key words: chaos, authentication watermark, fragile, tampering location

摘要： 针对现有空域脆弱认证水印算法定位精度低和安全性的问题，提出一种基于混沌的完全脆弱水印算法用于图像内容完整性认证和篡改定位。算法采用对原始图像分块的方法，计算图像块中各像素点高6位比特的灰度均值作为图像特征水印信息。利用混沌序列对水印信息进行加密和确定各水印比特嵌入的位置，篡改定位精度为2×2像素的图像块。实验结果表明，算法简单、安全性高，具有较好的实用性。

关键词: 混沌, 认证水印, 脆弱, 篡改定位