Editing TrueCrypt (section)

== Plausible deniability ==
TrueCrypt supports a concept called [[plausible deniability]],<ref name=deniability>{{cite web | title =Plausible Deniability | work =TrueCrypt Documentation | publisher =TrueCrypt Foundation | url =http://www.truecrypt.org/docs/?s=plausible-deniability | archive-url =http://arquivo.pt/wayback/20080226032737/http://www.truecrypt.org/docs/?s=plausible-deniability | url-status =dead | archive-date =26 February 2008 | access-date = 24 May 2014}}</ref> by allowing a single "hidden volume" to be created within another volume.<ref>{{cite web | title =Hidden Volume | work =TrueCrypt Documentation | publisher =TrueCrypt Foundation | url =http://www.truecrypt.org/docs/?s=hidden-volume | access-date =24 May 2014 }}</ref> In addition, the Windows versions of TrueCrypt have the ability to create and run a hidden encrypted operating system whose [[deniable encryption|existence may be denied]].<ref name=hiddenOS>{{cite web | title =Hidden Operating System | work =TrueCrypt Documentation | publisher =TrueCrypt Foundation | url =http://www.truecrypt.org/docs/hidden-operating-system | archive-url =https://archive.today/20130416074157/http://www.truecrypt.org/docs/hidden-operating-system | url-status =dead | archive-date =16 April 2013 | access-date =24 May 2014 }}</ref>

The TrueCrypt documentation lists many ways in which TrueCrypt's hidden volume deniability features may be compromised (e.g. by third-party software which may leak information through temporary files, thumbnails, etc., to unencrypted disks) and possible ways to avoid this.<ref>{{cite web | title =Security Requirements for Hidden Volumes | work =TrueCrypt Documentation | publisher =TrueCrypt Foundation | url =http://www.truecrypt.org/docs/?s=hidden-volume-precautions | archive-url =https://archive.today/20120917175346/http://www.truecrypt.org/docs/?s=hidden-volume-precautions | url-status =dead | archive-date =17 September 2012 | access-date =24 May 2014 }}</ref> In a paper published in 2008 and focused on the then latest version (v5.1a) and its plausible deniability, a team of security researchers led by [[Bruce Schneier]] states that [[Windows Vista]], [[Microsoft Word]], [[Google Desktop]], and others store information on unencrypted disks, which might compromise TrueCrypt's plausible deniability. The study suggested the addition of a hidden operating system functionality; this feature was added in TrueCrypt 6.0. When a hidden operating system is running, TrueCrypt also makes local unencrypted filesystems and non-hidden TrueCrypt volumes read-only to prevent data leaks.<ref name=hiddenOS/> The security of TrueCrypt's implementation of this feature was not evaluated because the first version of TrueCrypt with this option had only recently been released.<ref>{{cite conference |book-title=3rd USENIX Workshop on Hot Topics in Security |title=Defeating Encrypted and Deniable File Systems: TrueCrypt v5.1a and the Case of the Tattling OS and Applications |url=http://www.cs.washington.edu/homes/supersat/paper-truecrypt-dfs.pdf |author1=Alexei Czeskis |author2=David J. St. Hilaire |author3=Karl Koscher |author4=Steven D. Gribble |author5=Tadayoshi Kohno |author6=Bruce Schneier |date=18 July 2008 |url-status=dead |archive-url=https://web.archive.org/web/20081227025727/http://www.cs.washington.edu/homes/supersat/paper-truecrypt-dfs.pdf |archive-date=27 December 2008 |df=dmy-all }}</ref>

There was a functional evaluation of the deniability of hidden volumes in an earlier version of TrueCrypt by Schneier et al. that found security leaks.<ref name="yro.slashdot.org">[http://yro.slashdot.org/story/08/07/17/2043248/schneier-uw-team-show-flaw-in-truecrypt-deniability Schneier, UW Team Show Flaw In TrueCrypt Deniability]. Accessed on: 12 June 2012</ref>

=== Identifying TrueCrypt volumes ===
When analyzed, TrueCrypt volumes appear to have no header and contain random data.<ref>Piccinelli, Mario, and Paolo Gubian. "Detecting Hidden Encrypted Volume Files via Statistical Analysis." International Journal of Cyber-Security and Digital Forensics (IJCSDF) 3.1 (2014): 30-37.</ref> TrueCrypt volumes have sizes that are multiples of 512 due to the block size of the cipher mode<ref name=modes/> and key data is either 512 bytes stored separately in the case of system encryption or two 128&nbsp;kB headers for non-system containers.<ref>{{cite web | title =TrueCrypt Volume Format Specification | work =TrueCrypt Documentation | publisher =TrueCrypt Foundation | url =http://www.truecrypt.org/docs/volume-format-specification | archive-url =https://archive.today/20130619023456/http://www.truecrypt.org/docs/volume-format-specification | url-status =dead | archive-date =19 June 2013 | access-date =24 May 2014}}</ref> Forensics tools may use these properties of file size, apparent lack of a header, and [[randomness test]]s to attempt to identify TrueCrypt volumes.<ref>{{cite web |url=http://16s.us/software/TCHunt/tchunt_faq.txt |title=Archive |url-status=dead |archive-url=https://archive.today/20140507093925/http://16s.us/software/TCHunt/tchunt_faq.txt |archive-date=7 May 2014 |access-date=2 March 2017 |df=dmy-all }}</ref> Although these features give reason to suspect a file to be a TrueCrypt volume, there are, however, some programs which exist for the purpose of securely erasing files by employing a method of overwriting file contents, and free disk space, with purely random data (i.e. "shred" & "scrub"<ref>{{cite web | title = diskscrub - disk overwrite utility - Google Project Hosting | url= http://code.google.com/p/diskscrub/ |access-date=16 July 2014}}</ref>), thereby creating reasonable doubt to counter pointed accusations declaring a file, made of statistically random data, to be a TrueCrypt file.<ref name=deniability/><ref>{{cite web | title =Plausible Deniability | publisher =[[FreeOTFE]] | url =http://www.freeotfe.org/docs/Main/plausible_deniability.htm#level_3_heading_2 | archive-url = https://web.archive.org/web/20130124091432/http://freeotfe.org/docs/Main/plausible_deniability.htm#level_3_heading_2 | archive-date = 24 January 2013}}</ref>

If a system drive, or a partition on it, has been encrypted with TrueCrypt, then only the data on that partition is deniable. When the TrueCrypt [[boot loader]] replaces the normal boot loader, an offline analysis of the drive can positively determine that a TrueCrypt boot loader is present and so lead to the logical inference that a TrueCrypt partition is also present. Even though there are features to obfuscate its purpose (i.e. displaying a BIOS-like message to misdirect an observer such as, "Non-system disk" or "disk error"), these reduce the functionality of the TrueCrypt boot loader and do not hide the content of the TrueCrypt boot loader from offline analysis.<ref>[http://www.truecrypt.org/faq TrueCrypt FAQ] - see question
''I use pre-boot authentication. Can I prevent a person (adversary) that is watching me start my computer from knowing that I use TrueCrypt?''</ref> Here again, the use of a hidden operating system is the suggested method for retaining deniability.<ref name=hiddenOS/>