Oracle how to generate an md5sum hash of a string

FUNCTION md5 (p_input VARCHAR2)
   RETURN DBMS_OBFUSCATION_TOOLKIT.varchar2_checksum
IS
BEGIN
   RETURN LOWER
            (RAWTOHEX
                (UTL_RAW.cast_to_raw
                      (DBMS_OBFUSCATION_TOOLKIT.md5 (input_string => p_input)
                      )
                )
            );
END;