1. Introduction
Original biometrics are not changeable, so they can not be revoked and reissued even when they are stolen. Recently, a lot of biometric identification and verification systems have mushroomed, so it is likely that different databases store a user's same biometric template. If the user's biometric template in one database is attacked successfully, the user's biometric templates in the other databases are not secure anymore. Besides, original biometrics are likely to leak users' private information, such as gene defects, disease and so on. Since a user possesses only few biometric features, e.g. two irises and one face, so it is very important to protect biometrics.