full-disclosure - Re: Encrypted files and the 5th amendment

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Date: Tue, 12 Jul 2011 16:13:50 -0700
From: Tim <tim-security@...tinelchicken.org>
To: Ferenc Kovacs <tyra3l@...il.com>
Cc: "full-disclosure@...ts.grok.org.uk" <full-disclosure@...ts.grok.org.uk>
Subject: Re: Encrypted files and the 5th amendment

Hi Ferenc,

> check out the link in the last mail, seems to be what you are looking after.
> http://www.truecrypt.org/docs/?s=hidden-volume
> http://www.truecrypt.org/docs/?s=hidden-operating-system

Thanks I did read the first link at least.  This doesn't prevent
detection of *something else* on that disk though.

Once you give an investigator the key to the first partition/layer of
encrypted data, they can either see that the partition inside is too
small, or if the encrypted volume is within that volume in some way,
write a bunch of files and see when allocated space hits a wall.  One
way or another, TruCrypt has to prevent the hidden partition from
being overwritten.  

This is why I was saying that using compression (plus perhaps random
disk access; mixing hidden blocks in with non-hidden ones) could help
hide this discrepancy in sizes. However, the investigator can just run
the machine under a debugger to see what is really going on to
discover how much data should be left and where it should reside.

I agree with Thor though, if done carefully there are several ways to
argue "that's not mine" or "I forgot the password" or something
similar.

tim

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