256 bit AES on-the-fly cryptography - Fixed

[nickv_111]

Hello! I was wondering how I would go about implementing 256 bit AES cryptography on a directory. It needs to be transparent to other programs. I was thinking of using dm-crypt, but the problem there is wasted space. I mean, if I create a file called foo.img and it contains an encrypted filesystem, then I have a fixed-size filesystem. Now, what if I want to make it bigger? I'd have to make a new image, or potentially add more zeroes into that file and resize the filesystem. I have to add more space than I will probably take up. Also, if I remove files from that filesystem, then I have to somehow shrink the filesystem. This all gets very inconvinient. What would be ideal is a filesystem that automatically resizes according to how much space it needs. Something that is built for disk images. That way, if I added a file, it would change the disk image to take up more space. If I removed a file, it would shrink the disk image. Any other methods of 256 bit AES cryptography are welcomed. Mostly, the problem with using a disk image is space, so a dynamic filesystem should solve the problem.

Update:
I found a solution. When creating a .img, just do something like:
dd if=/dev/zero of=encrypted.img bs=1K count=1 seek=2097152
The above example creates a 2GB disk, but it initially starts as about 12K (size on disk, not actual size). When data is added, it expands.
Using that in conjunction with dm-crypt, I can now create AES encrypted filesystems that expand or contract depending on usage.

Thanks in advance,
Nick

[dblaci]

"I can now create AES encrypted filesystems that expand or contract depending on usage. "

I see, why it will expand on demand, but i don't think it will contract on freeing up space on the crypted fs.