Protect firebird database

Good Morning guys, I'm developing a system in C# WinFormswith the database in firebird 3that will work in internal networkof a company, the same follows a scheme Client X Server, where will have a server application with the database and clients will access the server bank. The problem is that after several searches, I did not find a viable solution to protect the database file, knowing that even though I change the default password of the user SYSDBA just a malicious user copies the database file to another server with any password and he will have access to the entire structure, including the data. How could I do to add an extra level of security to my database?