Biometric features provide considerable usability benefits. At the same time, the inability to revoke templates and likelihood of adversaries being able to capture features raise security concerns. Recently, several template protection mechanisms have been proposed, which provide a one-way mapping of templates onto multiple pseudo-identities.
While these proposed schemes make assumptions common for cryptographic algorithms, the entropy of the template data to be protected is considerably lower per bit of key material used than assumed owing to correlations arising from the biometric features.
We review several template protection schemes and existing attacks followed by a correlation analysis for a selected biometric feature set and demonstrate that these correlations leave the stream cipher mechanism employed vulnerable to, among others, known plaintext-type attacks.