Core functionality such as opaque error and utility functions.
Higher-level API with safer defaults.
HKDF (HMAC-based Extract-and-Expand Key Derivation Function) as specified in the RFC 5869.
HMAC (Hash-based Message Authentication Code) as specified in the RFC 2104.
PBKDF2 (Password-Based Key Derivation Function 2) as specified in the RFC 8018.