7 ms·

They can prove it sufficiently to force you to hand over your password. File systems have a particular behaviour, they allocate blocks in certain ways. Most not

They can prove it sufficiently to force you to hand over your password. File systems have a particular behaviour, they allocate blocks in certain ways. Most notably, they use all of the space available to them equally (or, pseudorandomly anyway). If a file system never allocates any data in the last N bytes, where N is a very large number, that is indication that the file system is treating the volume as Size-N. Since this behaviour is the signature of a hidden volume in a TrueCrypt container, that is "proof". It will be sufficient proof for a court of law. Essentially you are arguing that the file system implementation exhibited implausible behavior (it allocated only from the first N% of bytes), and that TrueCrypt exhibited implausible behavior ("ok, normally that would mean a hidden volume, but not in this case!"). All of which is to say, that TrueCrypt's implementation of Hidden volumes (as typically used by end users) is not actually plausibly deniable.

nknighthb 13y ago
> they use all of the space available to them equally (or, pseudorandomly anyway) This is simply false for many (if not most) filesystems, which preferentially write to blocks near the beginning of the disk. For spinning disks, random distribution of blocks would kill performance.
- fuzzbang 13y ago
  No, it is not false. The important thing with a spinning disk is locality of reference. You want the blocks which store the file content to be as close together as possible, to minimize the head seek times. This means you want as long a chain of contiguous blocks as possible. This does not mean that you want all those blocks to be at the beginning of the disk. In fact, the exact opposite. You want to start that chain at a random location so you are more likely to have a large number of contiguous unallocated blocks. See the implementation of HFS+ Extents, or Ext4, or UFS for examples of how this works.
  - nknighthb 13y ago
    A) You have forgotten basic physics. The beginning of the disk is faster. Locality is desirable but is not and has never been the only thing that matters. B) You have just named three uncommon filesystems that few people will ever use in the first place, much less with TrueCrypt.
    - schrodinger 13y ago
      HFS+ is not exactly uncommon
      - nknighthb 13y ago
        As a full-time Mac user for 8 years, and a Linux user for much of the decade before that, I am acutely aware of how common many filesystems, including HFS+, actually are. If OS X ever breaks 10% (and still uses HFS+ at that time), I'll reconsider my judgement of its commonality.
        schrodinger 13y ago
        It's over 7%, I still wouldn't call that uncommon and say few people use it. http://en.m.wikipedia.org/wiki/Usage_share_of_operating_systems http://en.m.wikipedia.org/wiki/Usage_share_of_operating_syst...
        davidcuddeback 13y ago
        I'm writing this from a computer with two partitions: one HFS+ running OSX and one Ext4 running Linux. These are both the default options when installing OSX (Mountain Lion) and Ubuntu 12.04, respectively: https://www.dropbox.com/s/x3cluigwaog8sad/gparted.png https://www.dropbox.com/s/x3cluigwaog8sad/gparted.png
        nknighthb 13y ago
        Of course you are. And if you took a poll of HN users, you might even find OS X + Linux near a majority. That has nothing at all to do with what filesystems the vast majority of people are using, much less what they'd be using with TrueCrypt.
  - deleted 13y ago
    [deleted]
i_are_crd 13y ago
Just because a filesystem isn't using all the space available in a partition does not mean that the rest of the space is being used by something else. Imagine I run `newfs -s 2097152 sd1p` where sd1p is actually 4194304 sectors. Now imagine sd1 is a softraid volume with a CRYPTO discipline. There's no way you can prove that the extra 2097152 sectors aren't being used, but there's also no way you can prove that they are.
- cnvogel 13y ago
  That's certainly true. But also (from a investigation point of view) more suspicious than a filesystem covering the whole harddisk, but only filled to 20%. That will always be a problem, as long as the "visible" filesystem just maps block 1..N directly onto encrypted blocks 1+k..N+k (with k being a constant offset), as it's currently the case e.g. in linux LUKS (I assume CRYPTO discipline in BSD is similar). The proper solution most likely would be to integrate a kind of block-mapping into the encryption software which allocates randomly distributed blocks from the encrypted harddisks whenever a filesystem begins to write to the blocks of an volume. This randomization algortithm then will be aware of all currently active "hidden partitions", but due to the randomness, a pattern to draw conclusions about the existence of other partitions would not emerge.
  - i_are_crd 13y ago
    "More suspicious" is meaningless. If you can't prove - with incontrovertible evidence and beyond any reasonable doubt - that there's something there, then there's plausible deniability.
    - nitrogen 13y ago
      Plausible deniability won't protect you from the "rubber hose" of a contempt charge.
deleted 13y ago
[deleted]
halviti 13y ago
It would be really nice if truecrypt implemented a feature whereby you could have a special password to use to render the secret partition un-usable, perhaps by rendering your existing password/key worthless.
- bhousel 13y ago
  Something like this wouldn't really protect you from law enforcement. They perform forensic disk duplication before mucking around with a drive. If you provide a fake password to TrueCrypt and it starts overwriting things, it would be pretty obvious to anyone investigating the drive what's going on.
- ReidZB 13y ago
  I'm not sure how such a feature would work or how useful it would be, for that matter. Maybe the TrueCrypt binary would attempt to decrypt the first X bytes of the partition under the "coercion" password and then check if it matches some known signature. If so, flip a bit in each encrypted block to scramble it. Problem: forensics people can use a write-blocking adapter on the original disk and simply make copies to try out the decryption. So, the feature sounds both irritating to implement and (worse) perhaps give a false sense of security to a novice.
- cshesse 13y ago
  http://www.truecrypt.org/docs/?s=hidden-volume http://www.truecrypt.org/docs/?s=hidden-volume is probably more what you want.

nknighthb 13y ago

> they use all of the space available to them equally (or, pseudorandomly anyway) This is simply false for many (if not most) filesystems, which preferentially write to blocks near the beginning of the disk. For spinning disks, random distribution of blocks would kill performance.

fuzzbang 13y ago
No, it is not false. The important thing with a spinning disk is locality of reference. You want the blocks which store the file content to be as close together as possible, to minimize the head seek times. This means you want as long a chain of contiguous blocks as possible. This does not mean that you want all those blocks to be at the beginning of the disk. In fact, the exact opposite. You want to start that chain at a random location so you are more likely to have a large number of contiguous unallocated blocks. See the implementation of HFS+ Extents, or Ext4, or UFS for examples of how this works.
- nknighthb 13y ago
  A) You have forgotten basic physics. The beginning of the disk is faster. Locality is desirable but is not and has never been the only thing that matters. B) You have just named three uncommon filesystems that few people will ever use in the first place, much less with TrueCrypt.
  - schrodinger 13y ago
    HFS+ is not exactly uncommon
    - nknighthb 13y ago
      As a full-time Mac user for 8 years, and a Linux user for much of the decade before that, I am acutely aware of how common many filesystems, including HFS+, actually are. If OS X ever breaks 10% (and still uses HFS+ at that time), I'll reconsider my judgement of its commonality.
      - schrodinger 13y ago
        It's over 7%, I still wouldn't call that uncommon and say few people use it. http://en.m.wikipedia.org/wiki/Usage_share_of_operating_systems http://en.m.wikipedia.org/wiki/Usage_share_of_operating_syst...
      - davidcuddeback 13y ago
        I'm writing this from a computer with two partitions: one HFS+ running OSX and one Ext4 running Linux. These are both the default options when installing OSX (Mountain Lion) and Ubuntu 12.04, respectively: https://www.dropbox.com/s/x3cluigwaog8sad/gparted.png https://www.dropbox.com/s/x3cluigwaog8sad/gparted.png
        nknighthb 13y ago
        Of course you are. And if you took a poll of HN users, you might even find OS X + Linux near a majority. That has nothing at all to do with what filesystems the vast majority of people are using, much less what they'd be using with TrueCrypt.
- deleted 13y ago
  [deleted]

i_are_crd 13y ago

Just because a filesystem isn't using all the space available in a partition does not mean that the rest of the space is being used by something else. Imagine I run `newfs -s 2097152 sd1p` where sd1p is actually 4194304 sectors. Now imagine sd1 is a softraid volume with a CRYPTO discipline. There's no way you can prove that the extra 2097152 sectors aren't being used, but there's also no way you can prove that they are.

cnvogel 13y ago
That's certainly true. But also (from a investigation point of view) more suspicious than a filesystem covering the whole harddisk, but only filled to 20%. That will always be a problem, as long as the "visible" filesystem just maps block 1..N directly onto encrypted blocks 1+k..N+k (with k being a constant offset), as it's currently the case e.g. in linux LUKS (I assume CRYPTO discipline in BSD is similar). The proper solution most likely would be to integrate a kind of block-mapping into the encryption software which allocates randomly distributed blocks from the encrypted harddisks whenever a filesystem begins to write to the blocks of an volume. This randomization algortithm then will be aware of all currently active "hidden partitions", but due to the randomness, a pattern to draw conclusions about the existence of other partitions would not emerge.
- i_are_crd 13y ago
  "More suspicious" is meaningless. If you can't prove - with incontrovertible evidence and beyond any reasonable doubt - that there's something there, then there's plausible deniability.
  - nitrogen 13y ago
    Plausible deniability won't protect you from the "rubber hose" of a contempt charge.

deleted 13y ago

[deleted]

halviti 13y ago

It would be really nice if truecrypt implemented a feature whereby you could have a special password to use to render the secret partition un-usable, perhaps by rendering your existing password/key worthless.

bhousel 13y ago
Something like this wouldn't really protect you from law enforcement. They perform forensic disk duplication before mucking around with a drive. If you provide a fake password to TrueCrypt and it starts overwriting things, it would be pretty obvious to anyone investigating the drive what's going on.
ReidZB 13y ago
I'm not sure how such a feature would work or how useful it would be, for that matter. Maybe the TrueCrypt binary would attempt to decrypt the first X bytes of the partition under the "coercion" password and then check if it matches some known signature. If so, flip a bit in each encrypted block to scramble it. Problem: forensics people can use a write-blocking adapter on the original disk and simply make copies to try out the decryption. So, the feature sounds both irritating to implement and (worse) perhaps give a false sense of security to a novice.
cshesse 13y ago
http://www.truecrypt.org/docs/?s=hidden-volume http://www.truecrypt.org/docs/?s=hidden-volume is probably more what you want.