Recently i've found this interesting tutorial:

http://flossstuff.wordpress.com/2011/08/07/using-a-file-as-a-storage-device/

It explains how to create an empty file, format it as ext4, and mount it as a device.

I'd like to know if it can be created as an encrypted ext4 file system. I've tried using palimpsest (the disk utility found in System menu) to format the already created file system but it doesn't works as it detects the file system being used. If I try to unmount the file system, it won't work neither because it doesn't detect the device (since it's not a real device like a hardrive or a usb drive).

So my question is, is there an option to create the file system encrypted from the begining? I've used these commands:

Create an empty file 200Mb size:

dd if=/dev/zero of=/path/to/file bs=1M count=200

Make it ext4:

mkfs -t ext4 file

Mount it in a folder inside my home:

sudo mount -o loop file /path/to/mount_point

Is there any way the mkfs command creates the ext4 encrypted asking for a decryption password?

I'm planing to use this as a way to encrypt files inside Dropbox.

Thanks for your time.