Truecrypt: Loss of space due to encryption

Does anyone know what is the loss of space due to encryption?
Eg, a 1 TB drive usually means 940GB of space.

How much space will I see if I encrypt the whole drive?

What if I have a hidden volume?

 

No space is lost.

 

Negligible if any due to TrueCrypt bootloader, installation folder, and system components (if that's the system drive, otherwise none). Nothing worth worrying about, especially with 1 TB of space.

Hidden volume is basically an obfuscated partition of your own choosing.

 

"What if I have a hidden volume?"

That depends upon the filesystem used for the outer/decoy volume. If you construct the outer volume using FAT32 your hidden volume can be MUCH larger than it will be if you use NTFS for the outer volume. That is not a TrueCrypt problem but simply the way NTFS sets itself up on the volume partition.

 

So the hidden volume size doesnt depend on the outer volume size?

What about other filesystems, eg ext3?

I have a 1TB disk the entire disk is a hidden volume. However I only get about 850 GB in the hidden volume.

 

Of course it depends upon the size of the outer volume. You can't put data in the "same place". The outer + hidden volume can't be > 1TB in this instance. The point I was making is that the selected filesystem used to create the outer volume (and the one "hosting" the hidden volume) largely effects the possible hidden volume size. Simply stated an outer volume NTFS system writes from the center out and that creates a great deal of wasted space that could be used for the hidden volume. The filesystem used for the hidden doesn't matter much. There are restrictions and permissions issues to consider as you pick your filesystem. Some of the liabilities of FAT32 can be overcome with third party software. e.g. auto spanning allows huge data files to be written for archival purposes and can be restored back to NTFS drives without issues at all.

 

Thanks for the explanation.

Suppose I create a 400GB outer volume, in which I only write 10GB.
Can the hidden volume in this case be 600GB or 922GB (say for FAT32)?

 

Somehow I think we are not fully connecting/communicating. If you have a 1 TB external drive and create a device based volume, the outer volume would be 1 TB minus a small amount to create the headers, parameters, etc... When you created the volume you would not select a size the entire 1 TB would be encrypted by TC. Then when you create the hidden volume it is at that point that you select the size of the hidden. The portion that you do not use creating the hidden volume would still be part of the outer volume.

Because the hidden volume is just that (hidden) TC will not show any size stuff for it when the outer volume is mounted. You can therefore simply overwrite the hidden volume and any adversary would not even know it exists. In other words the outer volume would have complete control of the entire 1 TB. It is necessary that TC works that way so the hidden volume stays that way. There are effective protection features but all that stuff is in the TC manual. Read it thoroughly more than once where volume creation is discussed.




You are asking some basic questions so I would strongly recommend getting familiar with TC before trusting 1 TB of data to it. Many users would also suggest starting with file based volumes while you get a handle on how TC works. Device based volumes are very unforgiving in the wrong hands. That said, I use them all the time but my data is backed up and the loss of any volume would not leave me with lost data.

 

Hmmm. Maybe I did something wrong when I created the hidden volume, cuz when I mount it I only see around 850 GB volume.

I had read the manual (I did all this a while back, thus my memory is a bit sketchy), and followed all the precautions; so I was surprised when I "lost" the space in the HDD.

I should the manual again.