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Truecrypt

TrueCrypt is an open source program to create and mount virtual encrypted disks in Windows Vista/XP/2000 and Linux and OS X as well as Full Disk Encryption on Windows. It provides two levels of plausible deniability (hidden values / no signatures to make a distinction from random data), on the fly encryption and supports AES, Serpent and Twofish. As of version 6.0 TrueCrypt now supports hidden Operating Systems under Windows only.

As of May 28, 2014 development to the software has been discontinued. the two major alternatives are VeraCrypt and CipherShed.

Detection

TrueCrypt volumes can be detected by

  • size of file or collection of clusters object modulo 512 is zero, that is size divided by zero has no remainder,
  • minimum size of object is 19KB, although by default is minimum 5MB,
  • contains no specific file signature throughout the entire object, and
  • has a high Shannon entropy or passes Chi-squared distribution test.

Forensic Acquisition

If you encounter a system that has a mounted TrueCrypt drive, it is imperative that you capture the contents of the encrypted drive before shutting down the system. Once the system is shutdown, the contents will be inaccessible unless you have the proper encryption key generated by a user's password. You may also need an additional datafile.

Attacks

The only option for acquiring the content of a dismounted TrueCrypt drive is to do a brute-force password guessing attack. AccessData's Password Recovery Toolkit and Distributed Network Attack (dna) can both perform such an attack, but DNA is faster.

TrueCrypt also supports keyfiles (it uses the first 1024 kilobytes of any file, but can also use it's PRNG to generate such keys). It is important to look for anything that might be used as a keyfile (such as a 1024k file on a USB stick).

Hidden volumes

Hidden volume is a volume hidden within the free space of another TrueCrypt volume. Even when the outer volume is mounted, it is hard to prove whether there is a hidden volume or not.

When a hidden volume is mounted, the operating system and third-party applications may write to non-hidden volumes information about the data stored in the hidden volume (e.g. filenames). It is important to look for such kind of information.

Previous versions of encrypted containers may be found in the journaling filesystems. It is important to track any changes within the free space of the outer container to detect presence of a hidden container.

Hidden Operating Systems

Hidden operating system is a system that is installed in a hidden TrueCrypt volume.

It is possible to detect network-enabled hidden operating systems by matching downloaded content (from a network dump) with data on a possible decoy system.

Investigator can also detect boot times by searching network dumps for IP packets with low IDs (only if Windows system is permanently connected to a LAN) and TCP timestamps.