You are logged on to a client. You do not have a secure connection from your client to the host where your Oracle database is running. Which authentication mechanism allows you to connect to the database using the SYSDBA privilege?

When connecting to Oracle over a non-secure network connection (without OS authentication support), Oracle uses password file authentication for privileged connections like SYSDBA. The password file stores credentials of users with SYSDBA/SYSOPER privileges. OS authentication works only when the client is on the same host as the database or has a trusted secure connection. Control files store database structure, not authentication data.