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veracrypt

title: VeraCrypt support in GNOME

User research

Research questions

Success

  1. How many people use VeraCrypt in Tails after our work in comparison with before?
  2. How many people who were using VeraCrypt outside of Tails but couldn't use it in Tails use it after our work?

Scope

  1. Which fraction of VeraCrypt volume are encrypted file containers? encrypted partitions?
  2. Are people encrypting their full operating system with VeraCrypt?
  3. Which fraction of users are using hidden volumes?
  4. Which fraction of users are using keyfiles? Why? How?
  5. Which fraction of users are using the old TrueCrypt format?
    • In VeraCrypt this requires checking the "TrueCrypt mode" check box.
  6. Can we rely on file containers having a .tc or .hc extension?

Behaviors

  1. How do people share files with other people who don't use Tails?

Technical knowledge

  1. How technical are VeraCrypt users? Tails+VeraCrypt users?
    • For example: Are they used to GNOME Disks?

Results of the online survey on file storage encryption

NB: By Tails+VeraCrypt we mean people who use both Tails and VeraCrypt, but not necessarily VeraCrypt in Tails already as this is currently for expert users only as it requires going through the command line.

Summary

  • Justification of our work:

    • 40% of Tails users are also VeraCrypt users, both inside and outside Tails.

    • 60% of Tails+VeraCrypt users only use VeraCrypt outside of Tails.

    • Most of Tails+VeraCrypt users are regular users of VeraCrypt.

    • VeraCrypt is of more interest to people who are not using Linux as their primary operating system.

    • VeraCrypt is still a reference when people think about encrypting files.

    • Integrating VeraCrypt in Tails will prevent dangerous behaviors:

      « I need to be able to open TrueCrypt file containers in Tails in order to move files securely between Tails and Windows. Right now, I have to copy my files unencrypted between Tails and Windows and this is quite dangerous. »

  • Definition of the scope of our work:

    • 85% of Tails+VeraCrypt users mostly don't use the .TC or .HC file extension.
    • 76% of Tails+VeraCrypt users use file containers.
    • 65% of Tails+VeraCrypt users use partitions.
    • 65% of Tails+VeraCrypt users use hidden volumes.
    • 55% of Tails+VeraCrypt users have legacy TrueCrypt volumes.
    • 42% of Tails+VeraCrypt users use keyfiles.

  • Technical knowledge of Tails users:

    • Tails is still quite complicated for Windows users but not that hard either.
    • A majority of our user base is "basic".

Methodology

We advertised an online survey on the homepage of Tor Browser in Tails between October 17 and December 1.

The survey was not advertised as being about VeraCrypt but as being about file storage encryption in general.

The following banner was displayed on https://tails.boum.org/home once every 20 views:

survey.png

We got 1011 complete answers (and zero spam!) for a participation rate of 1.97% (51431 views in total). We think this is a great success!

The structure of our survey is available as a LimeSurvey Survey Structure file: survey.lss.

We limited the mandatory questions to the bare minimum. Except for one open-ended question, we used only closed questions with multiple choices to maximize the answer rate and make it easier to analyze the results. Still, we allowed comments on many of the closed questions.

It was the first time that we asked our users to answer an online survey and seeing the high participation it seems to be a very good way of learning about our users and their needs. People seem eager to contribute to Tails by sharing information about themselves if done with their consent.

Here is a summary of our results.

How many people use VeraCrypt in Tails before our work?

Q: Do you use VeraCrypt?

Question Answers Fraction
No 418 41%
Yes, but only outside of Tails 238 24%
I don't know what VeraCrypt is 193 19%
Yes, both inside and outside of Tails 162 16%
Total answers 1011

  • 60% of Tails+VeraCrypt users only use VeraCrypt outside of Tails.

    These people are a first target of our work.

    Unfortunately, our survey didn't allow us to know if they don't use VeraCrypt in Tails because it's too complicated at the moment (it requires using the command line) or because they don't have a use for it. We should have added a another question about this in particular.

  • 40% of Tails users are also VeraCrypt users, both inside and outside Tails.

    This is a big overlap which proves that a lot of people who use Tails also have a need for VeraCrypt.

    After our work:

    • If this number increases, it could mean that integrating VeraCrypt in Tails made Tails useful for more people.

      These people are a second target of our work.

    • If this number decreases, it could mean that our user base expanded to include a bigger fraction of users who don't have a need for VeraCrypt. For example if they only use Tails to browser the Internet anonymously and not to exchange sensitive documents from Tails with other operating systems.

Q: How many VeraCrypt volumes do you have (not counting the hidden volumes inside them)?

Question Answers Fraction
2-5 183 52%
1 83 24%
6-10 45 13%
More than 10 39 11%
Total answers 350

  • Most of Tails+VeraCrypt users are serious and regular users of VeraCrypt.

    They have more than one VeraCrypt volume and not only curious about VeraCrypt or tried it once.

Comments on the questions

Our survey allowed people to add comments to some questions. Some people described the lack of VeraCrypt support in Tails as part of a workflow including Windows, often leading to dangerous practices. The comments were rewritten to prevent stylometry.

  • « When I move files between Windows and Tails, I have to remove the TrueCrypt encryption and copy the files unencrypted to another USB stick. Then I have to securely delete the files from the USB stick and that takes a lot of time. This is dangerous as an attacker could access my files during the process. »

  • « I need to be able to open TrueCrypt file containers in Tails in order to move files securely between Tails and Windows. Right now, I have to copy my files unencrypted between Tails and Windows and this is quite dangerous. »

Which fraction of VeraCrypt volume are encrypted file containers? Encrypted partitions?

Q: What type of VeraCrypt volumes are you using?

Question Answers Fraction
Only encrypted file containers 117 32%
Mostly encrypted file containers, some encrypted partitions 89 24%
Mostly encrypted partitions, some encrypted file containers 75 20%
Only encrypted partitions 74 20%
I don't know the difference between encrypted partitions and encrypted file containers 13 4%
Total answers 368

  • The difference between encrypted file containers and partition is well understood.

  • 76% of Tails+VeraCrypt users use file containers.

  • 65% of Tails+VeraCrypt users use partitions.

Are people encrypting their full operating system with VeraCrypt?

Q: Is your Windows operating system encrypted using VeraCrypt?

Question Answers Fraction of Tails+Windows users Fraction of Tails users
No 135 72% 35%
Yes 49 26% 13%
I don't know 3 2% 1%
Total answers 187

Which fraction of users are using hidden volumes?

Q: How often do you create a hidden volume in your VeraCrypt volumes?

Question Answers Fraction
Sometimes 159 44%
Never 119 33%
Always or almost always 50 14%
Most of the time 27 7%
I don't know what a hidden volume is 7 2%
Total answers 362
  • 65% of Tails+VeraCrypt users use hidden volumes.

Which fraction of users are using keyfiles?

Q: What do you use to protect your VeraCrypt volumes?

Question Answers Fraction
Only passwords 211 58%
Mostly passwords, sometimes keyfiles 130 36%
Mostly keyfiles, sometimes passwords 18 5%
Only keyfiles 6 2%
Total answers 365
  • 42% of Tails+VeraCrypt users use keyfiles.

Which fraction of users are using the old TrueCrypt format?

Q: How many of your volumes are TrueCrypt volumes and how many are VeraCrypt volumes?

Question Answers Fraction
All my volumes are VeraCrypt volumes 151 45%
All my volumes are TrueCrypt volumes 92 27%
Most of my volumes are VeraCrypt volumes, some are TrueCrypt volumes 49 14%
Most of my volumes are TrueCrypt volumes 47 14%
Total answers 339

  • 55% of Tails+VeraCrypt users have legacy TrueCrypt volumes.

    The reasons given for that in the comments to this question include:

    • Not having done the effort of migrating.
    • Having to migrate too much data to be practical (1TB!).
    • Not trusting VeraCrypt has it hasn't been audited.

Can we rely on file containers having a .tc or .hc extension?

Q: Does the name of your file containers include the .TC or .HC extension?

Question Answers Fraction
Never 91 39%
I don't know what the extension of my file containers is 72 31%
Sometimes 33 14%
Always or almost always 27 12%
Most of the time 8 3%
231
  • 85% of Tails+VeraCrypt users mostly don't use the .TC or .HC file extension.

How technical are Tails users? Tails+VeraCrypt users?

Q: Which operating system other than Tails do you use the most?

Question Tails users Fraction Tails+VeraCrypt users Fraction
Windows 456 45% 201 52%
Debian or Ubuntu 355 35% 129 34%
macOS 69 7% 26 7%
Arch Linux 21 2% 9 2%
Linux Mint 16 2% 4 1%
openSUSE 12 1% 6 2%
Fedora 12 1% 3 1%
Qubes OS 10 1% 6 2%
Total answers > 10 951 384

By OS families:

Question Tails users Global market share Different in VeraCrypt usage among Tails users
Windows 456 48% 91% +4%
Linux 426 45% 3% −4%
macOS 69 7% 6%
Total answers 951

  • We suppose that people choose Linux over Windows or macOS because of technical reasons, ethical reasons, or both. Both are also good reasons to use Tails, either because their technical skills make it easier to get started or use Tails or because their ethical motivation aligns with the values of Tails.

    There is a huge difference between the fraction of Tails users and the global market share for Windows (in negative) and Linux (in positive) but at the same time, almost half of Tails users are otherwise mostly Windows users. So it seems like Tails is still quite complicated for Windows users but not that hard either.

  • Tails+Windows users are using VeraCrypt more than Tails users in general (+4%). This confirms that VeraCrypt is of more interest to people who are not using Linux as their primary operating system.

    This aligns with our objective of making Tails easier to integrate in workflows involving other operating systems.

Q: How familiar are you with GNOME Disks?

Question Answers Fraction
I can use GNOME Disks to do advanced operations 438 43%
I don't know what GNOME Disks is 410 41%
I can use GNOME Disks to do basic operations 163 16%
Total answers 1011

This seems to mean that:

  • A majority of our user base is "basic": not well-versed in Linux and GNOME, not skilled enough to manipulate partitions, or not using Tails to manipulate sensitive documents outside of the persistent volume.

  • A good share of the rest of our user base is "advanced" and more technically skilled and knowledgeable about Linux and GNOME.

Q: Imagine that you want to share a big video footage with someone else who doesn't use Tails. You can meet in person or communicate online. For security reasons, you want the exchange to be encrypted. How would you do that?

Due to the huge numbers of answers (626) to this question which was very open-ended, it is challenging and very time consuming to extract insights from all the answers.

We manually flagged the encryption techniques mentioned in the first 472 answers (75%) to get an overview of what Tails users would do to exchange sensitive information between Tails and another operating system.

While flagging the answers, we flagged some techniques that were only mentioned implicitly. For example, some people implicitly referred to:

  • LUKS when they proposed to store the footage in the persistent volume of a Tails USB stick and exchange this USB stick in person.
  • OpenPGP when they proposed to encrypt the file doing right-click ▸Encrypt… from the file browser.

The answers often included mixed strategies to either:

  • Design both online and offline strategies, as the question made it possible to either meet in person or communicate online.
  • Combine several encryption techniques, for example to encrypt and send the footage using some techniques and to exchange a password or other credential information using other techniques.
  • Design several strategies depending on the threat model or technical knowledge of the person they were sharing the footage with.

We cannot know from if people would know how to apply the strategies they described. For example, if they already know how to use the techniques that they mentioned or if they only heard of them.

Encryption technique Mentions Fraction
OpenPGP 134 28%
- OpenPGP (unspecified) 79 17%
- OpenPGP (asymmetric) 39 8%
- OpenPGP (symmetric) 16 3%
VeraCrypt 107 23%
I don't know 78 17%
LUKS 49 10%
ZIP with password 49 10%
OnionShare 46 10%
Signal, WhatsApp, Telegram 25 5%
Total answers analyzed 472

  • VeraCrypt was the second most frequently mentioned encryption technique.

    VeraCrypt is still a reference when people think about encrypting files.

  • We were surprised to see OpenPGP as the most frequently mentioned encryption technique. This could either mean that:

    • Tails users are especially knowledgeable about OpenPGP or only heard of it as an encryption technique.

    • Tails users rely a lot seahorse-nautilus which allows to encrypt files from the file browser (right-click ▸Encrypt…). This allows to use symmetric encryption ("password encryption") without the need to master the complex key management of OpenPGP.

  • We were also surprised to see OnionShare mentioned almost as frequently as LUKS or ZIP with password. Good news for Micah Lee!

Scope of our work

We structure the scope of our work in four iterations, based on our preliminary research work on user needs and technical feasibility.

We will implement and upstream each iteration one after the other and go as far as the budget allows.

  1. Unlocking partitions (tails#15214 (closed))

This iteration is the bare minimum for this project but also the foundation work which makes all subsequent iterations possible. It covers:

  • The unlocking of partitions, which is relevant to 65% of Tails+VeraCrypt users.

  • The opening of hidden volumes, which has a very good cost/benefit ratio and will please the users of this very popular feature.

  • The opening of legacy TrueCrypt volumes, which will come with almost no UX or backend cost.

  • The opening with keyfiles and opening of system partitions, which will also be very cheap to add to the custom dialogs that we will already have to implement for the opening of hidden volumes.

  1. Unlocking file containers (tails#15223 (closed))

This iteration extends the work done on the unlocking of partitions to also unlock file containers.

File containers are very important to support as 76% of Tails+VeraCrypt users use file containers. They are also interesting because using a single file to store a whole file system is a possibility which is not offered by the other encryption techniques in Tails.

But they are more challenging in terms of user interactions and integration code:

  • It's a new concept for users ("mounting a file").

  • We cannot rely on file containers having a .TC or .HC extension as discovered during the survey.

  • GNOME Files cannot automatically identify and flag file containers as such.

  • The integration in the sidebar of GNOME Files of opened file containers will require to patch the GTK library which was not expected initially.

  • Displaying the file name of the containers when unlocking it through GVfs will require an additional patch upstream.

  1. Creating and modifying partitions and containers (tails#15227 (closed))

Since our main objective for integrating better VeraCrypt in Tails is to allow for cross-platform sharing of encrypted files, we consider making it possible to create VeraCrypt volumes in Tails as optional since users can continue creating volumes from their other operating systems. This iteration covers:

  • The creation of new partitions, for which we already have a solid UX design.

  • The creation of new file containers, which will be harder to discover for users but will almost come for free once we support creating new partitions.

  • The modification of existing volumes, which will be very similar to the creation of new volumes.

  1. VeraCrypt Mounter (tails#15043 (closed))

VeraCrypt Mounter is a very simple application wrapper that we designed and tested. It makes it easier for users to learn how to use VeraCrypt in Tails and makes it faster to open file containers. VeraCrypt Mounter would only be available in Tails.

If we cannot create VeraCrypt Mounter in time, we will replace it with a link to our documentation which should lead to similar success rates but a bit less comfort for first time users.

Non goals

Opening of loop-AES and dm-crypt volumes. Loop-AES and dm-crypt volumes are other encryption formats that are indistinguishable from VeraCrypt volumes while they are locked (both look like random data). Even if some of our work could be make it easier to support Loop-AES and dm-crypt, we won't do that because these formats are not popular enough.

User interface

Changes to GNOME Disks

Unlock dialog in GVfs

Detecting VeraCrypt volumes

In contrast to LUKS, VeraCrypt and TrueCrypt volumes do not have a cleartext header, but are completely encrypted (see the VeraCrypt Volume Format Specification). As a result, VeraCrypt/TrueCrypt volumes cannot be distinguished from random data. This means that the best we can do is to indicate to the user that a partition / file seems to be encrypted or random data, and therefore is a candidate for being a VeraCrypt/TrueCrypt volume.

To determine whether data seems to be encrypted or random, we use Pearson's chi-squared test. This test is often used to test for randomness.

When trying to determine whether a partition (or whole device) is a VeraCrypt/TrueCrypt volume, we don't want to read more than necessary, to avoid slowing things down too much. Because non-encrypted filesystems usually start with a header, which is very non-random, we only perform the chi-squared test on these first 512 Bytes.

The chi-squared test requires a p-value, for which to reject the hypothesis that the data is random. We choose 1/10.000.000.000 as the p-value, which means that in one of 10 billion cases, the test will issue a false negative, i.e. the test says the data is non-random/non-encrypted, even though it actually is random/encrypted. From this p-value, we derive the following lower and upper limits for the chi-squared value (using the scipy chi2 module):

>>> from scipy.stats import chi2
>>> chi2.ppf([0.1**10, 1-0.1**10], 255)
array([ 136.49878495,  425.92327131])

We round these values to the closest integer. So for chi-squared values between 136 and 426, we accept the hypothesis that the data is random/encrypted.

We will not be able to prevent false positives as effectively as false negatives. Since we treat all random-looking partitions as TrueCrypt/VeraCrypt candidates, we will definitely have false positives, because there are other use cases for random looking partitions, for example plain dm-crypt, headerless LUKS, or LoopAES partitions. This cannot be avoided, therefore we have to clearly indicate to the user that a partition is not definitely a TrueCrypt/VeraCrypt partition, but only a candidate.

We don't expect false positives for unencrypted filesystems, because the chi-squared value clearly indicates that they are not encrypted. Some examples for chi-squared values of (more or less) common filesystems, calculated with the above method:

Filesystem Chi-squared
bfs 113013
exfat 115672
ext2 130560
ext3 130560
ext4 130560
fat 56629
minix 130560
ntfs 61937
vfat 56651