Biometric encryptions combine biometric authentication and cryptography. It can possibly provide accurate and convenient authentication with the benefits of privacy and security. In this paper, we propose three irreversible transformation schemes using four irreversible transformation functions for face features; order number transformation scheme, feature value transformation scheme and two dimensional transformation schemes. In experiment, we compared the authentication performance and the security of each scheme. Faces from ORL database are taken as examples to illustrate the performance. Then we use one arbitrary face from the database to compare the reconstructed faces for each transformed feature. The results show that the reconstructed face images from the transformed feature values are much different from the original face images. The scheme 2, order number transformation, can be secure enough by increasing the percentage of many-to-one area. It has almost the same authentication performance as original face features.%生物特征加密技术由于生物特征认证技术和密码学方法组成.它在为生物认证系统提供精确性和便捷性的同时,也保证了生物模板的隐私性和安全性.本文针对有序人脸特征,设计了四种形态的不可逆变换函数,并将其运用到三种不可逆变换方案中.我们设计的不可逆变换方案包括:位置变换方案,特征值变换方案以及二维变换方案.在实验阶段,我们对比了三种变换方案产生模板的认证性能和安全性能,并以任意一幅人脸的变换模板为例进行重构,重构后的人脸图像与原始人脸有很大差异.实验结果表明,位置变换方案通过增加多对一区域方式来增加认证系统安全性能,且认证性能与原始生物特征几乎相同.
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