1. A method, comprising: obtaining biometric data; selecting a first biometric descriptor at a first level of a hierarchy of biometric descriptors using the biometric data; obtaining a first key component associated with the first biometric descriptor; selecting a second biometric descriptor at a second level of the hierarchy of biometric descriptors using the biometric data; obtaining a second key component associated with the second biometric descriptor; and obtaining a cryptographic key using at least the first key component and the second key component.