Biometrics is the utilization of biological characteristics (face, iris, and fingerprint) or behavioral traits (signature and voice) for identity verification of an individual. Biometric authentication is gaining popularity as more trustable alternative to password-based security systems as it is relatively hard to be forgotten, stolen, or guessed. On the other hand, biometric data which can uniquely identify a person (e.g. fingerprints and iris patterns) can be used to track individuals, linking many separate databases (where the person has been, what the user has purchased etc.), which raises privacy concerns.