Biometric authentication based on template protection has attracted attention in the past decade. In the discussion on the security of these systems, however, the content of biometric information is assumed to be sufficiently large, and real conditions of biometric features have not yet been reflected. This paper focuses on a biometric cryptosystem using a fuzzy commitment scheme and demonstrates correlation between fingerprint bit strings by using our method for evaluating the content of biometric information. Additionally, attacks to guess biometric bit strings, which take advantage of correlation between them, are explained, and the security against these attacks is theoretically and experimentally discussed.