Complete Deniability

I’ve written before about the limited usefulness of plausible deniability, especially in relation to software like TrueCrypt, a hard drive encryption program.

The gist of plausible deniability with TrueCrypt is this: You have multiple encrypted hard drive partitions. When your enemy forces you to reveal your keys, you reveal the low-cost key, and the enemy sees some data that he doesn’t care about and sends you on your merry way. The ‘real’ stuff you want to hide is still hidden.

This works if two conditions are true:
* The enemy doesn’t know you employ a product with plausible deniability
* The enemy can merely detain you

If those conditions aren’t true, you’re in big trouble. Say a violent group gets you and your data. They know TrueCrypt has plausible deniability, and they really want your data. You’re going to be tortured until they get what they want, it’s that simple, and ugly.

Now, the worst possible scenario is that you can’t give up ‘your data’ because it doesn’t exist. But only you know that. The bad guys think you have it and they know you have plausible deniability. You’re completely screwed.

For this reason I’ve been against plausible deniability systems for defending against all threats (yes, TrueCrypt would still be fine from hiding that porn you have stashed away on your home PC).

This changed when Cal Harding introduced the concept of Complete Deniability. That is, you can prove that you have no more plausible deniability.

Here’s how it can work: With TrueCrypt, you could have a utility that, once inside a locked data set, could be given a set of keys and ensure that those keys account for all readable data and all blocks of the storage device. Because TrueCrypt is open source, the bad guys can trust this utility to verify that you’re no longer hiding anything. They can review the source and compile it themselves, if they wish.

But, good news for you, you get to go home. Because even bad guys don’t like to waste their time and you’re not otherwise terribly interesting. Odds are you’re not getting your laptop back once the bad guys find your porn bank, though.