Identification and secret-key generation in biometric systems with protected templates

In the system that we investigate here two terminals observe the enrollment and identification biometric sequences of a group of individuals. The first terminal forms a secret key for each enrolled individual and stores the corresponding helper data in a public database. These helper data on one hand facilitate reliable reconstruction of the secret key and on the other hand allow determination of the individual's identity for the second terminal, based on the presented biometric identification sequence. All helper data in the database are assumed to be public. Since the biometric secrets produced by the first terminal are used e.g. to encrypt data, the helper data should provide no information on these secret keys. In this paper we determine what identification and secret-key rates can be jointly realized by such a biometric identification system. This problem is closely related to the study of the biometric identification capacity [Willems et al., 2003] and [O'Sullivan and Schmid, 2002] and the common randomness generation problem [Ahlswede and Csiszár, 1993].