Traditional biometrics recognition system is vulnerable to privacy invasion when the stored biometric template is compromised. This in turn will suffer from permanently loss as biometric template is not replaceable In this paper, we propose a key extraction scheme which locks a secure transformed fingerprint bitstring via a novel dynamic quantization mechanism. During authentication stage, the key is extracted from the secure mixture when a genuine fingerprint is presented. A number of keys can be assigned to different applications and could be revoked if the key was compromised. The proposed method retrieve key reliably from a genuine fingerprint up to 99.5% success rate. We perform several security and experimental analyses and the results suggest that the scheme is feasible in practice.