Super User is a question and answer site for computer enthusiasts and power users. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I would like to encrypt my disk, as while I don't have anything illegal, there are some things I would rather not be interrogated about or cause confiscation of my belongings while going through customs in the US or other countries.

I have 1 300gb hdd, which has about 100gb free. I would like to encrypt the contents, but do not want to be forced to give up the encryption key.

The solution to this seems to be to use a truecrypt hidden volume. However, my concern, is to allow my data to grow as needed, naturally. I was considering using a hidden OS partition, but wonder how reliable this is.

So, can a hidden OS partition be any size, and can it be protected against files written outside of it?

Is there a way to hide the size of a hidden volume? If Someone sees my 'main' volume, and see it only has 1gb of files, will this show as 299gb free, or will the hidden volume visibly be taking up space?

Otherwise, the used space would be a giveaway..., if so, is there any way to overcome this?

Is it possible to boot windows without a password, i.e. normally, and then boot my 'real' hidden OS volume only with a password?

share|improve this question
up vote 4 down vote accepted

The hidden partiton is inherently completely hidden - it lurks within the free space of the normal "outer" encrypted partition. There is no record of it, nor it's size, and you can only access it by providing it's own password.

There are two ways of mounting the outer encrypted partition. Only by it's own password, or also accompanied by the hidden partition's password to inform the system of the existence of the hidden partition.

If you mount it without the hidden partition's password, the system has no knowledge of it, and there's no way to know there's data to be found in the free space. Since it has no knowledge of it, the hidden data is not protected, and any writes done to the free space are potentially overwriting hidden data. Tough luck.

If you mount it by also providing the hidden partition's password, the system will know where the hidden data is, and the hidden data will be kept protected. It prevents any overwrites with an error. It will not move the hidden data around to avoid the overwrite, because this would compromize it's security - it will only prevent the overwrite with a write error (in fact also making the whole system read-only until a remount).

So in everyday use, you'd have to always mount it with both passwords - but if you're forced to provide a password, you can only provide the normal password, and there will be no way to know that you have created a hidden partition too. There is no huge "hidden.dat" -file or such, only free space, which if examined, will show random incoherent bytes.

Of course, if you're using the hidden area from an OS that's not itself running in a hidden partition, there is a risk that the OS or some of the applications used for handling the data betray the existence, or even store a cached copy, of files in the hidden partition.

In your case even the OS would be within the hidden partition, creating a hidden operating system. In this case, there's no risk of it being compromized. (Of course there are always risks from outside the system, like getting keylogged, monitored by hidden cameras, remotely viewed by psychics, socially engineered by spychicks, abducted by aliens, and so on... but you get the idea.)

You'd also need to have a decoy operating system on an different partition (using the outer encrypted partition for data), for plausible deniability. You'd also need to use the decoy quite often for non-sensitive work so that it wouldn't look suspicious. So yes, I would imagine size might become a problem there, since writes to the data area (that contains the hidden operating system within the free space) have a good chance of failing (when colliding with the hidden data) unless there's a lot of truly free space. But I'm not familiar with usage of hidden operating systems, and there might well be some countermeasure for this that I'm not aware of.

The TrueCrypt documentation has quite a lot of stuff about this, and it's well worth reading.

share|improve this answer
In fact I went ahead and asked a further question about using the decoy system here:… – Ilari Kajaste Oct 12 '09 at 20:33
Exactly what I wanted to know, that used space is not detectable! Thankyou. – Bill Grey Oct 14 '09 at 18:53

The best way would be not to encrypt your whole drive, but simply create a volume on the drive (as a file)...

Some tips:

  • Use a file archive extension (zip, 7z, rar)... It's rather easy to claim if they come upon it that the file contained a backup and seems to be corrupted now. [Don't use zip for a volume over 4GB... Zip files cannot exceed 4GB, having a larger file would arose suspicion].
  • Or use a unknown extension (.sync for example) and if asked, say it is used to backup a smart device which isn't with you.
  • Don't create a volume with a round number of bytes (say exactly 10GB). That's way too suspicious.
  • If they ask why TrueCrypt is installed, just say you have an external hard-drive encrypted with it for security against thieves, which is not with you right now.
share|improve this answer
You don't have to install Truecrypt. You could also rename it's main exe and leave it in a system folder, or your temp folder or some other fairly buried folder. – pipTheGeek Oct 4 '09 at 20:31

It is really up to you what to do... If you are stopped, they can request your encryption keys and detain you if you refuse to reveal them.

I personally would just opt for either full drive encryption using Bitlocker on Windows, or if that is a no go, I would use Truecrypt and just normally set up a drive from a file.

If you go to any effort to hide, it would just look a lot more suspicious than having the files unencrypted.

Sorry, I know that this is not really what you want to see, but if you really do not want anyone to see your files, you are probably just best off leaving your laptop at home and using remote desktop or remote access or similar.

share|improve this answer
Well, Hidden volumes are an answer to the problem you pose, I'm just unsure to their effectiveness if the hidden volume is too large in size. – Bill Grey Oct 4 '09 at 20:32

I don't think that truecrypt would be able to make an OS volume that would boot normally. If you are encrypting the OS partition then I'm not sure how much you would gain by using a hidden volume. You would also have to install your OS twice, once in the hidden volume and once in the ordinary volume, and make the ordinary OS look full enough to be your actual OS.

Obviously I don't know what it is that you want to keep hidden, but I would agree with the other answers that making a volume in a file would be a better option.

Lastly, encryption is restricted in some countries. For instance, France had laws that meant encryption was tightly controlled and you could be required to hand over keys. Some brief research shows that they are changing these laws.

Have you considered using an on-line backup service like Mozy to store the files you want kept secret. During travelling you could leave a backup copy on removeable media at home and delete them from your laptop. Mozy make a network drive available that you can use to restore any files you want over the internet. Or you could encrypt the files and put them on a service like MS sky drive, or whatever they call it now.

share|improve this answer
Yes, truecrypt can encrypt a partition upon which an OS sits, as well as provide you a bootloader. It can also do hidden ones: Your online backup suggestion is a good one though... but I'd strongly suggest truecrypting stuff up and then sending it along the wire rather than relying on Mozy's "security". – PriceChild Aug 9 '11 at 9:55

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .