Controlling leakage of biometric information using dithering

Fuzzy extractors allow cryptographic keys to be generated from noisy, non-uniform biometric data. Fuzzy extractors can be used to authenticate a user to a server without storing her biometric data directly. However, in the Information Theoretic sense fuzzy extractors will leak information about the biometric data. We propose as alternative to use a fuzzy embedder which fuses an independently generated cryptographic key with biometric data. As fuzzy extractors, a fuzzy embedder can be used to authenticate a user without storing her biometric information or the cryptographic key on a server. A fuzzy embedder will leak in the Information Theoretic sense information about both the biometrics and the cryptographic key. While both types of leakage are important, information leakage of the biometric data is critical since the cryptographic key as opposed to biometric data can be renewed. We show that constructing fuzzy embedders which leak no information about the biometrics is theoretically possible. We present a construction which allows controlling the leakage of biometric information, but which requires a weak secret at the decoder called dither. If this secret is compromised the security of the construction will degrade gracefully.