Best practice for securing sensitive data in plain text file?
Currently I am working on a C linux daemon that takes user input for an SQL connection string, then stores the information into a local conf file (client side). The purpose of the daemon is to submit data to an SQL database at a set interval in that every time the daemon is loaded it will look to the local conf for the SQL connection string. Also by using the command line argument -c, the user can reconfigure the SQL connection string in the event that the information changes. Would anyone be willing to share a way of securing this conf file so that it is not plain text. Keep in mind that I still need to be able to access and read in from the conf file as there is other conf settings present. Thanks in advance guys.
Edit: I do eventually plan to use SSL to submit the data between the client side and the SQL server.
The (only?) way to secure the file is to change its permissions to make it readable only to the user that runs the daemon.
Eg. if you are running the daemon as user 'foo' and group 'foo', you should:
chown foo.foo my-conf-file chmod 600 my-conf-file
(Or even chmod it to 400 to prevent accidental modification, but I guess in this case you'll lose the -c option functionality).
NOTE: Also remember that it is quite dangerous to pass connection strings on the command line since they will be visible from the process listing!
You could also use some GPG stuff to encrypt the file, but I don't see the point there since then you have to protect the key you use to decript the file, and you get the exact same problem as before.
If you have no place to keep your secrets, cryptography will not help you. If your daemon is somehow able to decode password not using any secret, then anyone can do this too. So you have to rely on system protection, such as file access mode flags to keep keys.