I was wondering if an encrypted filesystem could be read while it was opened if:

a)s/he has physical access to the box while it's turned on.
b)the attacker does not have a login to the box.
c)the only link it has to the internet is ssh.
d)only root can mount external media sources (usb drives/cd's)

If so, what precautions could I take against this? I need a way to secure files on a server, but have it so some relatively average computers users can access the files contained on it (basically I don't feel like educating them about encryption keys). The only thing I'm worried about is a nosey administrator on campus trying to peak into it, not the NSA or anyone.

Thanks!

EDIT: typo in the title...my bad.

An encrypted file system ONLY makes data on a disk inaccessible to people who do not have the encryption software and key when the file system is not mounted. The protection is circumvented when the encrypted file system is mounted.

You should be able to apply that information to the various circumstances listed in your question.

The system administrator can see the data on the encrypted file system only when that file system is mounted.

Other people logged on to the computer can see the information if it is not properly configured via permissions (i.e. chmod 700) and ownership.

Malware can see the data if it is running under an account that can see the data.

Some encryption software keeps the encryption key in RAM as long as the machine is turned on. Some types of file systems will write the unencrypted data to a journal file. The operating system may write unencrypted data to a swap file. The best way to keep others from seeing the data is to turn the machine off when you are not using it.

Comment: I am a little bit concerned when you say that you want to keep the system administrator from seeing the data. Of course there are legitimate reasons for this which is why I answered the question. On the other hand this site has a policy against helping people circumvent the proper use of machines used in education, business, and whatever. Use your knowledge for good and not for evil. :-)

Oops...well I don't know how nosy the admin is yet, I'd just prefer everything to remain private; if s/he has to access it, I'd like them to ask me directly instead of going behind me.

Thanks for the info though. Looks like I might be persuing a different method. =)

You could have an encrypted file mounted with a loop device. This will protect the data when it isn't mounted. A root user will be able to read it when it is however. You will need to have a pass phrase to protect it. You will need root access to mount an encrypted partition or an encrypted file.

I'm guessing that you want to protect private customers' information from administrators on a remote system. You need to encrypt the data itself. You can use crypto functions in mysql for example to protect the users data in a soho environment.