Defeating Encrypted and Deniable File Systems:
TrueCrypt v5.1a and the Case of the Tattling OS and Applications
Alexei Czeskis1, David J. St. Hilaire1, Karl Koscher1, Steven D. Gribble1, Tadayoshi Kohno1, Bruce Schneier2
We examine the security requirements for creating a Deniable
File System (DFS), and the efficacy with which the TrueCrypt
disk-encryption software meets those requirements.
We find that the Windows Vista operating system
itself, Microsoft Word, and Google Desktop all compromise the
deniability of a TrueCrypt DFS. While
staged in the context of TrueCrypt, our research highlights several
fundamental challenges to the creation and use of any DFS: even
when the file system may be deniable in the pure, mathematical
sense, we find that the environment surrounding that file system can
undermine its deniability, as well as its
We hypothesize some extensions of our discoveries to regular (non-deniable)
encrypted file systems.
Finally, we suggest approaches for overcoming these
challenges on modern operating systems like Windows. We analyzed TrueCrypt version 5.1a (latest available version during the writing of the paper); Truecrypt v6 introduces new features, including the ability to create deniable operating
systems, which we have not studied.
A deniable file system (DFS) is one where the
existence of a portion of the file system can be hidden from view.
This is different from an encrypted file system, where files and
directories are visible yet unintelligible. In a DFS, the very
existence of certain files and directories cannot be ascertained by
Deniable File Systems are receiving increasing attention both in popular media and in academia due to the current political environment in which personal laptops are being searched, sometimes even seized, at international border crossings. In response, the EFF (Electronic Frontier Foundation) and CNET have published guides on securely crossing the border with your laptop [3,5]. Both guides recommend, as one of the most secure options, using a DFS to hide the existence of data. The suggested tool is an open-source disk-encryption software package called TrueCrypt, hence we use it as the focus of our case study.
The TrueCrypt package for Microsoft Windows3
includes the ability to make a portion of the disk deniable.
While TrueCrypt allows for a large number of configurations, a
typical configuration might be as follows: Alice creates a regular
(non-deniable) encrypted file system on her laptop, protected by
some password she knows. Inside that encrypted file system, she has
the option to also create a deniable file system, protected
by a second password. TrueCrypt refers to these inner, deniable
file systems as hidden volumes. These hidden volumes are
claimed to be deniable since, unless she reveals that
second password to an adversary, it should be impossible for that
adversary to determine whether Alice's regular encrypted file
system contains an encrypted hidden volume or not.
We examine both the security requirements for creating
a DFS, and how well TrueCrypt's solution meets those requirements. Our
results show that deniability, even under a very weak model,
is fundamentally challenging. The natural processes
of the Windows operating system, as well as
applications like Microsoft Word or Google Desktop,
can leak significant information outside of
the deniable volume. For example, lists of recently changed
documents, audit logs of recent file actions, and data saved by
application programs can all serve to inhibit deniability. As our
results suggest, any DFS will not only have to encrypt and hide data
- as file systems like TrueCrypt do - but must also erase
any traces of that data left by the operating system through normal
The rest of the paper is organized as follows. Section 2 discusses
relevant threat models for deniable file systems. Section 3 describes
the TrueCrypt approach in more detail. Section 4
describes our principal information leakage attack vectors against
deniable file systems, which we experimentally evaluate in the context
of TrueCrypt hidden volumes.
We propose potential defensive directions in
Section 5, as well as discuss the potential
applicability of our results to non-deniable (regular) encrypted
file systems. We summarize some related works in
Section 6, and then close in
Addendum and Document History.
We analyzed the most current version of TrueCrypt available at the
writing of the paper, version 5.1a. We shared a draft of our paper
with the TrueCrypt development team in May 2008. TrueCrypt version
6.0 was released in July 2008. We have not analyzed version 6.0,
but observe that TrueCrypt v6.0 does take new steps to improve
TrueCrypt's deniability properties (e.g., via the creation of
deniable operating systems, which we also recommend in
Section 5). We suggest that the breadth of our
results for TrueCrypt v5.1a highlight the challenges to creating
deniable file systems. Given these potential challenges, we
encourage the users not to blindly trust the deniability of such
systems. Rather, we encourage further research evaluating the
deniability of such systems, as well as research on new yet
light-weight methods for improving deniability.
2 Threat Model
Alice is a human-rights worker, and keeps sensitive information on
her computer. The data is encrypted, but she is concerned that the
secret police will seize her computer and, noticing that part of the
disk is encrypted, threaten her - or worse - for the key. She
needs to protect her data in such a way that it is deniable:
there must be nothing that would indicate to the secret
police that there are hidden files on her computer.
If she denies the existence of certain files, and the police
later discover the existence of those files on her computer, she
could be vulnerable to severe punishment.
Encrypted file systems such as Microsoft's BitLocker
will not suffice; encryption does not hide the existence of data, it
only makes the data unintelligible without the key. This is precisely
the sort of scenario that requires a DFS.
However, it is exactly these restrictive security requirements that make a DFS
difficult to implement.
Breaking the security of a DFS does not require decrypting the data;
it only requires proving that (or in some cases simply providing
strong evidence that) the encrypted data exists.
There are several threat models against which a DFS could
potentially be secure:
Clearly there is a point where the adversary is so powerful that
even a DFS won't protect Alice. If Alice is working on files in the
deniable portion of her computer when the secret police break down
her door, she will not be able to deny their existence. If the
secret police are able to obtain disk snapshots at close enough
intervals, the existence of any deniable files will be
obvious, since seemingly random bytes on the hard drive will change. Still,
we would like any DFS to provide as much security as possible
along the continuum of increasingly severe threat models.
In this paper, we examine attacks against a DFS
under the most restrictive threat model: one-time access.
Clearly, a successful attack under this threat model implies a successful
attack under the less restrictive threat models.
- One-Time Access. The attacker has a single snapshot of the disk image. An example would be when the secret police seize Alice's computer.
- Intermittent Access. The attacker has several snapshots of the disk image, taken at different times. An example would be border guards who make a copy of Alice's hard drive every time she enters or leaves the country.
- Regular Access. The attacker has many snapshots of the disk image, taken in short intervals. An example would be if the secret police break into Alice's apartment every day when she is away, and make a copy of the disk each time.
TrueCrypt is a free disk encryption application that provides
on-the-fly-encryption for Microsoft
TrueCrypt has the ability to create deniable hidden volumes.
hidden volumes are optionally - hence deniably - placed
inside non-hidden, regular encrypted volumes.
Outer (Non-Hidden, Regular) Encrypted Volumes.
A regular (non-hidden) TrueCrypt encrypted volume can be stored (in
encrypted form) as a file on top of a regular file system. For
example, a TrueCrypt encrypted volume could be stored as the file
C:. Alternately, a TrueCrypt encrypted
volume could occupy a dedicated partition on a disk. In either
case, the encrypted volume is referred to as a TrueCrypt container.
To decrypt a TrueCrypt container, the user must provide the
password and keyfiles (if there were any) that were used when
creating the volume. We do not describe the details of the TrueCrypt
encryption and decryption algorithms since we (largely) treat
TrueCrypt as a black box.
TrueCrypt provides a DFS through a feature known as a hidden
volume. A hidden volume is a TrueCrypt volume stored inside the
container of a regular, non-hidden TrueCrypt volume.
A hidden volume requires its own
password, and - if the hidden volume's password is not supplied (or supplied incorrectly) -
the hidden volume's data will appear as random data. Since free space
in a regular (outer) TrueCrypt volume is, according to the
documentation, filled with random data, this provides plausible
deniability to an attacker under the one-time access threat
Namely, such an attacker, even if given access to the
password for the outer encrypted volume, should not be able to
determine whether the random data at the end of the outer encrypted
volume is really just random data, or whether it corresponds to an
encrypted hidden volume.
The TrueCrypt documentation concludes that
a person with a hidden volume could therefore convincingly deny the
hidden volume's existence.5
Interface to Windows. The TrueCrypt application exposes
several options to users wanting to mount a regular or hidden
volume, including: mount type (whether the volume should be mounted
as a fixed file system or a removable file system), writability (read-only
or not), and mount point (e.g., E:).
TrueCrypt also exposes sufficient information to the Windows
operating system to allow Windows to mount and interact with the
contents of TrueCrypt volumes (after the relevant passwords or other
credentials are entered). We return to specifics of this
exposed information later.
Information Leakage from Below.
The TrueCrypt documentation already includes some recommendations
and caveats for the use of hidden
volumes.6 The principal recommendations are to be cautious about the media on top of which a TrueCrypt
hidden volume is stored. Namely, suppose a TrueCrypt volume (and
its associated outer volume) are stored on a USB stick. Then
wear leveling (a physical property of how data is sometimes
stored on USB sticks) could reveal information about the existence
of the hidden volume. The TrueCrypt documentation similarly advises
against storing a TrueCrypt container on top of a journaling file
system. We stress that these existing recommendations focus on
being cautious about the media underlying a TrueCrypt
container. Our research focuses on information leakage from above -
i.e., information that might leak out about a TrueCrypt hidden volume
when the hidden volume is mounted and the operating system and
applications are interacting with the hidden files.
The TrueCrypt documentation also rightly observes that an adversary
with greater than one-time access (i.e., intermittent or regular
access) to the TrueCrypt container could discover the existence of a
TrueCrypt hidden volume; for example, by analyzing the differences
between multiple snapshots of a
TrueCrypt container. Our analyses therefore focus on the weaker
case in which the adversary is only given one-time access to the
4 Information Leakage from Above
We evaluate three general classes of information leakage vectors
against deniable file systems using TrueCrypt's hidden volumes as a case study.
These classes all share the following traits: the information
is leaked out about the hidden volumes and the files contained
therein after the hidden volume is mounted, and the
information is not securely destroyed after the hidden volume is
In more detail, the three classes of information leakage that we consider
We present experiments showing that the above information leakage
classes are not hypothetical. Our results highlight the
subtleties and challenges to building deniable file systems.
- Through the Operating System. Modern operating
systems are complex, with many unexpected and unintuitive
behaviors. Operating systems are not designed with the goal of
preserving the deniability of deniable file systems. Therefore, the
natural execution of an operating system may leak information about the
existence of a deniable file system, even if the deniable file
system is cryptographically secure.
- Through a Primary Application. A deniable file system
does not exist in isolation. Rather, people create deniable file
systems in order to hide content that they are currently using and plan
to use in the future. In order to use those files, these
people must run an application (like Microsoft Word, Adobe PhotoShop, and so
on). These applications, which are not designed to preserve
deniability, may leak information about the existence of those files.
- Through a Non-Primary Application. Many computers
often run non-primary applications, or applications that (at first
glance) appear to be unrelated to the files stored on a hidden
volume. For example, many users run applications like Google
Desktop and anti-virus software that might interact poorly with the
deniability of a hidden volume.
4.1 Example Leakage Through the OS: Shortcuts
The TrueCrypt documentation observes that information about
TrueCrypt is stored in the Windows Registry.7 This information reveals the fact that a person used
TrueCrypt on his or her machine, and the locations at which TrueCrypt
volumes were mounted (e.g., E:).
But this information does not reveal
the container's file name, location, size, nor the
type of volume that was mounted.
Hence, the Windows registry does not appear to directly compromise
the deniability of a TrueCrypt hidden volume.
We do not consider the Windows registry further, but instead turn
to another artifact of the Windows operating system:
A shortcut, or .lnk file, is a link to another
file. For example, the shortcut C:.lnk might link to
the file D:.doc; double-clicking on
C:.lnk would cause Microsoft Word to open D:.doc.
These links provides a convenient way to access files and folders.
Shortcuts can be created in multiple ways, including by users and by
programs. Perhaps surprisingly, Windows automatically
creates shortcuts to files as they are used, and in Vista these
shortcuts are stored in a folder called Recent
Items that is located in C:. For example, if a user recently opened the files
E:1.doc and E:2.doc, shortcuts to these
two files would be in the Recent Items directory. A wealth
of information can be obtained from a .lnk file, including the real file's file name, location, attributes, length, access
time, creation time, modification time, volume type, and volume
serial number of the file system on which the real files are
Suppose Alice stores the file BadStuff.doc on a hidden
volume, edits that document while on a plane, and then closes Word
and unmounts the hidden volume before passing through customs. If
the customs officer inspects the Alice's disk, he or she will quickly
discover that Alice was editing this file - which alone might be
significantly compromising information for Alice. Worse, even if the
file had an innocuous name like GoodStuff.doc, the customs
officer can exploit the volume serial number field in the
.lnk file in the Recent Items directory to garner
significant evidence that Alice was using a hidden volume.
As additional setup for the latter, recall that in the U.S. it is a
crime to lie to a federal law enforcement
officer . This means that if Alice chooses to
answer a custom agent's question about whether she has a TrueCrypt
hidden volume, Alice must answer truthfully. Suppose first that a
customs agent asks if Alice uses TrueCrypt. The only answer Alice
can supply is "yes," since evidence of TrueCrypt's usage is stored
in the Windows registry (and cannot be safely or reliably deleted, according
to the TrueCrypt documentation). Next, suppose that the
customs agent asks Alice to identify and mount all the TrueCrypt
volumes on her machine, as well as all her other mountable file systems
and USB sticks, and that she does so except for the hidden
The critical observation here is that each of these mounted volumes
has a unique volume serial number. While this volume serial number
is not available in the registry, it is available to
applications after the volumes are mounted and is also stored
in the shortcut .lnk files. The customs agent can now
compare the volume serial numbers in the relevant .lnk files
to the volume serial numbers for all the volumes that Alice mounted
and, if there is discrepancy, he knows that there
exists or existed a file system that Alice is not disclosing.
While the above scenario is described in real-time; that is,
happening while Alice is in the presence of the customs agent, the
customs agent could collect similar evidence by simply cloning
Alice's hard drive and, either at that time or later, asking her to
supply all her passwords. We view the above scenario as plausible
given the current political
environment [3,5,8], and
even more likely in other countries. Even if such a scenario
were unlikely, we view the potential for such a scenario - coupled
with the well-known fact that users have difficultly following
security protocols - to be sufficiently risky to advocate not trusting
in the deniability of TrueCrypt hidden volumes.
4.2 Example Leakage Through the Primary Application: Word Auto Saves
In order to dampen data loss in the case of a crash, many applications use backup or recovery files. When editing a file, the application will create a local copy of the file and record in it all changes made to the original file. When the application successfully closes and saves all modifications, the backup file is removed. It makes sense that these applications store backup files locally in case an external volume is prematurely unmounted (such as removing a USB stick before it finishes syncing, or an emergency power-off). For example, Microsoft Word 20079 by default creates auto-recover files in
The consequence of this auto-recover mechanism is that a file that was originally stored in a hidden volume has now been copied to the local hard disk. Although Word removes the backup file after the user closes the primary file, Word does not invoke secure delete. We were repeatedly able to recover previously edited files that were stored on the hidden volume by running a simple, free data recovery tool.
Specifically, we first ran cipher /w:c:\10 to clean up any dirty free space. We then mounted a hidden TrueCrypt volume on which we had previously stored seven copies of the Declaration of Independence of the United States of America titled as variants of OverthrowGovernment.doc. We then opened and edited these files with Microsoft Word, saved the changes to the original files, exited Word, and unmounted the hidden volume - all things an ordinary user might be reasonably expected to do while using a TrueCrypt volume.
Without rebooting, we ran a simple, free data recovery tool.11
The number of files we recovered and their quality was not consistent on every experiment, since the free space on the C: drive can be changed at any moment. Nevertheless, we were able to fully recover most of the documents in their entirety from the Word auto-recovery folder. After a fresh experiment that
included a reboot after the hidden volume was unmounted,
half of the files were still recoverable. We hypothesize that we could have recovered even more data if we had performed more sophisticated techniques such as examining the individual file blocks on disk.
Furthermore, in cases when an application is prematurely terminated - for example, during a crash or by a kill command - the auto-recover file will persist on the local disk in clear view and will be recovered by Microsoft Word without the TrueCrypt volume being mounted. This means that just pulling the power on one's computer at the sight of authorities will not safeguard a file if it was open or in the process of being edited.
While Microsoft Word presents users with the ability to prevent auto-saves from occurring through the preferences dialog, other applications may not. An attacker can use information gleamed from these files - as well as other information leakage from the primary
application - to not only infer that a hidden volume exists, but also recover some of its contents.
4.3 Example Leakage Through A Non-Primary Application: Google Desktop
Non-primary applications may also access the files stored on a hidden volume.
For example, desktop search applications are becoming more
prevalent, allowing users to quickly navigate their
computers. However, in addition to merely indexing the files on a
computer to aid in searching for files, at least one desktop search
application - Google Desktop12
- includes an additional feature
that presents problems for a DFS. This feature is the ability to
view previous states of websites and files such as Microsoft Word
documents. According to Google, the purpose of this caching
feature is to recover accidentally deleted files or to simply view
an old version of a file or web page.
The default installation of Google Desktop does not provide for the
indexing or caching of files; however, this basic mode of operation
limits Google Desktop's ability to assist the user. When installing
Google Desktop, the user merely needs to select the "Enhanced Search"
option to enable both the indexing and caching of certain files types.
To protect privacy and to optimize searched areas, the user is
provided with the ability to choose which folders to include and
exclude from indexing. However, Google Desktop claims that all
fixed drives will be indexed by default. As a user opens documents,
modifies them, and saves them, Google Desktop caches snapshots of
the files and stores them for later viewing.
Google Desktop provides not only the latest cached
version of a file but also multiple versions of a file cached at different
times. These cached files could provide an attacker with not only
the current state of a document but also a view of its evolution
In our tests we created a Word document called
OverthrowGovernment.doc in a TrueCrypt hidden volume and added
sections of the Declaration of Independence to the document. With
Google Desktop installed13 and running, we edited and saved the
document numerous times. After unmounting the TrueCrypt hidden
volume, we were easily able to recover a number of snapshots of our
file by merely searching for any word contained in the file. We
were able to repeat these results irrespective of the volume's mount
point (any drive letter F, G, H, L) or mount type (normal/fixed and removable medium). See
Thus, to protect oneself, the
user cannot rely on only tweaking TrueCrypt's settings, but rather
must understand the dangers presented by the non-primary application
itself. In the case of Google Desktop, one of two choices could be
made to prevent Google Desktop from leaking file contents out of
TrueCrypt volumes. The user can either forgo the features of Google
Desktop Enhanced Search, forcing it into a limited mode of
operation, or the user can make the conscious choice to either shut
down Google Desktop or pause its indexing whenever using a TrueCrypt
volume. This burden of needing to understand exactly how a
non-primary application interacts with a TrueCrypt volume
underscores the difficulties of implementing and using a DFS.
Figure 1: Information leakage through Google Desktop. The TrueCrypt hidden volume has been unmounted, and yet we can recover numerous snapshots of the hidden file's contents.
While non-primary applications such as Google Desktop may allow the
user to pause its actions at arbitrary points, other non-primary
applications may not provide the user with this capability even if
the user understands the dangers posed by the application. In
addition, malicious applications, like botnets or viruses, could
obviously compromise the deniability of
a hidden volume in ways that the user cannot predict nor prevent.
5 Future Directions
5.1 Defensive Directions
It may be possible to address each of the above-mentioned
information leakage vectors in isolation. For example, to counter
the Windows shortcut-based attack, TrueCrypt may consider using the
same serial number for all volumes, serial numbers that are a
function of the mount point, random serial numbers each time, or
some combination of the above. Other ad hoc approaches may
also be successful at addressing this particular information leakage
However, such ad hoc approaches do not solve the
fundamental problem: the operating system and
applications can leak significant information about the existence
of, and the files stored within, a hidden volume. We have
identified three broad classes of information leakage vectors, with
concrete examples for each class. However, we are sure that other
examples likely exist, waiting to be discovered. The problem is
therefore much more fundamental, and addressing it
will require rethinking and reevaluating how to build a
true DFS in the context of modern operating systems
To create a DFS, it seems inevitable that the
operating system (and perhaps the underlying hardware) must assist
in the deniability. New operating system architectures like
HiStar  could help ensure that information about a
DFS does not leak to other portions of a system.
However, the strong information flow guarantees afforded by such
architectures may be overkill to prevent the most typical information
leaks. Moreover, these architectures require significant changes to
the operating system.
An approach that may work well with existing operating systems is to
install a file system filter that disallows a process any write access
to a non-hidden volume (or the registry, under Windows) once that process
reads information from a hidden volume.14 Robust applications
should accept the fact that they cannot store temporary files and
either alert the user that a feature is not available (like
auto-recovery) or silently fail (like saving a shortcut to a recent
document). Less robust applications may not work under this new restriction.
However, the fact that applications no longer work tells the user that
application will leak potentially private information. The user can then weigh
the risks and benefits of using the application in an unprotected manner,
and manually allow the application to work outside the protection scheme.
While this does not provide 100% protection, it may
work well enough to stop typical information leaks. For example, a process
may leak information about a hidden volume to another process via IPC or a
network connection, and that second process may write this information to
a non-hidden volume. However, we hypothesize that these situations are
rare in practice, and that this minimalist information flow approach will
substantially improve the deniability of hidden volumes; users must still
lulled into a false sense of additional security greater than what is
Another possible direction would be to create a "TrueCrypt Boot Loader" that,
upon entering one password, decrypted the disk one way and booted the OS.
And, upon entering a different password, decrypted the deniable portion of
the disk and booted the OS in the deniable partition. (Addendum: such
a boot loader is now implemented in TrueCrypt v6.0.)
We leave other specific directions as open problems.
5.2 Reflections to Regular Disk Encryption
Reflecting on the second and third classes of information leakage
(Sections 4.2 and 4.3), we stress
that they also seem applicable to regular (non-deniable) disk
encryption systems in which only a subset of all the user's entire
disks are encrypted and in which a user does not deny the existence
of the encrypted regions but does refuse to divulge the passwords.
In our future work, we would like to investigate exactly how well
these attack vectors apply to regular encrypted disks and volumes.
We also wish to explore methods for limiting information leakage in
situations when whole disk encryption is not used (for example: when
using an encrypted USB drive or virtual disk with a non-encrypted
system disk). In summary with regard to disk encryption, in
situations where there is a need to protect the privacy of
individual files, the safest strategy appears to be to encrypt the
full disk with tools like PGP Whole Disk Encryption.
6 Related Works
We mention significant related work in-line above, but recall here
the long history of steganographic and deniable file systems
beginning with the work of Anderson et al. ,
and followed by both academic publications [6,7]
as well as non-academic but widely circulated applications (include
TrueCrypt); see also .
A related thread of research, though not targeting
deniability, is focused on encrypted file systems, again including
both published research such Blaze's encrypted file system for
commercial systems such as PGP Whole Disk Encryption and BitLocker,
and open source systems, including TrueCrypt.
There are large bodies of research focused on information leakage
in other contexts.
We demonstrate three broad classes of information leakage vectors
against the deniability of a TrueCrypt hidden volume: leakage
from the operating system; leakage from the primary application;
and leakage from non-primary applications.
We believe that our work underscores a new direction for the design
and analysis of deniable file systems - a direction that must
include provisions for protecting against information leakage from
the external environment that interacts with the
deniable file system while the file system is mounted.
Addressing these issues is both timely and important, as evidenced
by the current political environment in which computers are searched
at international borders and the broad media discussions about
the advantages of deniable file systems like TrueCrypt's,
On the other hand, even if a DFS is secure, it might not be a good
solution to Alice's secret-police problem. Just as an attacker
would not be able to prove the existence of secret data under such a secure
DFS, the same attacker wouldn't be able to prove
the non-existence of deniable data. If the
secret police continue to demand that Alice disclose the password to
such a deniable file system, there is no way for her to prove that
her configuration doesn't have such a volume.
Deniability cuts both ways, and sometimes that's not a benefit.
R. Anderson, R. Needham, and A. Shamir.
The steganographic file system.
In Information Hiding, 1998.
A cryptographic file system for UNIX.
In CCS, 1993.
EFF answers your questions about border searches.
The Windows shortcut file format.
Security guide to customs-proofing your laptop.
A. D. McDonald and M. G. Kuhn.
StegFS: A steganographic file system for Linux.
In Information Hiding, 1999.
B. Oler and I. E. Fray.
Deniable file system: Application of deniable storage to protection
of private keys.
In International Conference on Computer Information Systems and
Industrial Management Applications (CISIM), 2007.
"Taking your laptop into the US? Be sure to hide all your data
The Guardian, 15 May 2008.
Deniable file system.
N. Zeldovich, S. Boyd-Wickizer, E. Kohler, and D. Mazières.
Making information flow explicit in HiStar.
In OSDI, 2006.
1Dept. of Computer Science and Engineering, Univ. of Washington.
The current version of TrueCrypt (version 5.1a)
also provides Linux and OS X implementations, but neither
of these implementations support deniable file systems,
and hence we do not consider these implementations in this paper.
Prior to a recent code rewrite, older versions of Linux TrueCrypt
supported hidden volumes.
5We have not verified that the
free space at the end of a regular TrueCrypt volume is in fact
filled with random data. Such an analysis would be orthogonal to
our principle focus of studying TrueCrypt's black-box interaction
with the operating system and surrounding applications. A failure
to fill the free space with random data would, however, allow for a simple
attack against the deniability of the hidden volume.
8Our experiments were with Windows Vista
Business edition with Service Pack 1, though our results apply more broadly.
9Word 2007 (12.0.6311.5000) SP1 MSO (12.0.6213.1000)
Part of Microsoft Office Home and Student 2007.
10A Windows command that writes 0x00, 0xFF, and then random data to all free space blocks on a disk.
11http://tokiwa.qee.jp/EN/dr.html; DataRecovery 2.4.2.
evaluated version 5.7.0805.16405-en-pb.
13Default install with Enhanced Search enabled.
14It may also be desirable
to mark certain applications, such as Google Desktop, as never being allowed to read a hidden volume, lest they be permanently tainted with knowledge
of the forbidden data.
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