Password protected cryptosystem is commonly adopted nowadays. The main shortcoming of such cryptosystem is the lack of the connection between the user and password. The special biometric protected cryptosystem adopting biometric key scheme, which binds the biometric template and cryptographic key monolithically, can be a good solution to the problem. The biometric key scheme is devised in such a way that the cryptographic key cannot be retrieved without a successful biometric authentication. A novel biometric key scheme based on modular secret sharing is proposed in this paper. The feasibility and high security have been proved by theoretical analysis and experiments. In the experiment of combining iris recognition with the scheme, the probability for illegitimate user to retrieve the cryptographic key is zero; the probability for legal user fail to retrieve the cryptographic key is 0.0571. The optimal biometric key is 2645 times more difficult for an attacker to retrieve the cryptographic key comparing to the legitimate user.

数字水印技术是实现多媒体数据版权保护的一种有效手段。随着关系型数据库的广泛使用，也随之产生了在关系型数据库中嵌入水印信息的需求。通过在关系型数据库中所嵌入的版权信息，可以将数据库与其拥有者联系起来，从而实现数据库的版权保护。本文提出了一种可以在数据库中嵌入具有实际意义字符串的水印算法，并介绍如何通过调整算法中的参数，实现不同的鲁棒性和不可见性需求。在Oracle数据库中所进行的仿真实验结果表明，该算法可以在实际数据库中得到很好的应用。

几何攻击是目前困扰数字水印领域发展的问题，现有的抗几何攻击的水印技术存在诸多缺陷和不足。本文提出一种基于时域的抗几何攻击水印技术，利用边框这一简单的图形通过对其检测和提取，完成对几何失真参数的检测。考虑到实际应用中存在噪声的影响，用中值滤波和锐化增加了几何参数估计的鲁棒性。利用检测获得的几何失真参数对图像进行校正，使图像基本恢复原图从而无失真地提取水印。同时本文探讨了诸多文献尚未提及的几何失真恢复问题，提出一种模板匹配的方法恢复图像。仿真实验证明，该方法在含水印图像受到几何攻击后，仍可无失真地提取水印。

A digital watermarking technique based on the discrete fractional Fourier transform (DFRFT) is proposed. The original image is transformed by DFRFT, and the DFRFT coefficients of the original image are modified by the information of watermark. Experimental results show that the proposed technique is robust to lossy compression attack.

本文提出一种基于多分辨率分解的可视数字水印技术。利用图像的多分辨率分解技术，相同分辨率层次的灰度级数字水印嵌入到对应的相同分辨率层次的原始静态图像之中，使水印对原始图像具有自适应性。由于水印的嵌入过程是基于原始图像的不同分辨率层次之间的关系，所以水印的提取不需要原始图像。实验结果表明本文提出的数字水印技术，经一些图像处理操作和有损压缩后仍是健壮的。