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Well, it's not actually too problematic. Usually there are forms of metadata which persist and can store this sort of information. So let's assume that you didn't go for whole-drive encryption, and your text editor shows in its recent history "/media/truecrypt1/where-I-buried-him.txt", written on the evening of the murder: so the police believe that somewhere on your computer is a text document revealing where the victim was buried. And since it's my story, we'll suppose that you're completely innocent and that this is a fictional story you've been writing for the last three months, but you're worried that your bizarre murder fiction sounds eerily similar to the circumstances that the other guy died, and might tend to sound incriminating or character-assassinating to a jury.

Even if TrueCrypt didn't protect their encryption with a message-authentication code, the police would still notice that you had given them a decrypted file without a filesystem on it -- much less a filesystem containing /media/truecrypt1/where-I-buried-him.txt . If they have already convinced a judge to force you to decrypt the file, they could just tell the judge "this person is being uncooperative!" and your hijinks will get you nowhere.

Now suppose that they do not have this, but convince the judge that since you have TrueCrypt, and this is the only random-looking file on your computer, that this is probably your TrueCrypt archive. They convince the judge to threaten you with contempt if you don't decrypt it, through whatever means they have available to them. Well, TrueCrypt containers are always meant to be directories -- i.e. they always hold file systems -- and so you'd best decrypt this container into a file system! But that severely restricts your defense.

TrueCrypt will let you do something different: to provide a 'wrong key' which indeed decrypts the device to a valid file system. This is their 'hidden volume' system.

I'm kind of mixed in my reaction to TrueCrypt's hidden partitions, for other reasons. But they address the problem that you've identified, and I haven't figured out a better solution.




Well, TrueCrypt containers are always meant to be directories -- i.e. they always hold file systems -- and so you'd best decrypt this container into a file system! But that severely restricts your defense.

TrueCrypt is not meant to hold file systems any more than a hard drive is. There is nothing stopping you from not creating a file system on your truecrypt volume and just storing garbage in it - or use another encryption software on top of it.

TrueCrypts hidden-volume feature is quite meaningless in most cases (my opinion) due to the way it is likely used. If you present a decryption key that gives access to a filesystem that does not match what was expected then you are in trouble.

Especially the hidden OS feature... So you have been using this laptop on multiple occasions the last week (of which we have proof) but according to the filesystem you presented to us this system haven't been used for over a month.

The same goes for a hidden volume. Unless you actively use it as often as you use your device (which is really cumbersome to do right) you might just be better of without it since exposing it will tell them way more than you want to tell them (for starters it will tell them that you are actively lying and having made precautions in order to try and get away with lying).


Your last paragraph is actually the "mixed reactions" that I was having. It seems like for hidden volumes to work right, you need to constantly be using the outer volume. That's fine, there are plenty of applications you might want to encrypt but might not need to hide from the police -- passwords and emails, perhaps, or legally-downloaded-and-possessed pornography, or a journal, or something like those.

The problem is, due to what I guess is something of a flaw in the central idea, you ultimately have to provide the password for your inner volume when you do all of these things which don't involve it. So now your private data is split up over two drives, which is at least somewhat questionable, and also the "mundane" drive requires the "important" password.

This may be acceptable if you're collecting a small cache of text documents which you believe could harm a corporation -- then you say "no, I don't have those articles, see, this really is just my porn stash, please don't hurt me. But a criminal or a government -- no, they're willing to be patient and they're perhaps willing to peek at your password input prompts with webcams or audio-recordings. They would know that there's an extra password being entered every time you decrypt that file.




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