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A minimalistic commandline tool to manage encrypted volumes aka The Crypto Undertaker

More information and updates on website: https://www.dyne.org/software/tomb

Get the stable .tar.gz signed release for production use!

Download it from https://files.dyne.org/tomb

For the instructions on how to get started using Tomb, see INSTALL.

What is Tomb, the crypto undertaker?

Tomb aims to be a free and open source system for easy encryption and backup of personal files, written in code that is easy to review and links well reliable GNU/Linux components.

Tomb's ambition is to improve safety by way of:

• a minimalist design consisting in small and well readable code
• facilitation of good practices, i.e: key/storage physical separation
• adoption of a few standard and well tested implementations.

At present, Tomb consists of a simple shell script (Zsh) using standard filesystem tools (GNU) and the cryptographic API of the Linux kernel (cryptsetup and LUKS). Tomb can also produce machine parsable output to facilitate its use inside graphical applications.

How does it work?

To create a Tomb, do:

 $ tomb dig -s 100 secret.tomb
 $ tomb forge secret.tomb.key
 $ tomb lock secret.tomb -k secret.tomb.key

To open it, do

 $ tomb open secret.tomb -k secret.tomb.key

and after you are done

 $ tomb close

or if you are in a hurry

 $ tomb slam all

  Syntax: tomb [options] command [arguments]

  Commands:

   // Creation:
   dig     create a new empty TOMB file of size -s in MiB
   forge   create a new KEY file and set its password
   lock    installs a lock on a TOMB to use it with KEY

   // Operations on tombs:
   open    open an existing TOMB (-k KEY file or - for stdin)
   index   update the search indexes of tombs
   search  looks for filenames matching text patterns
   list    list of open TOMBs and information on them
   ps      list of running processes inside open TOMBs
   close   close a specific TOMB (or 'all')
   slam    slam a TOMB killing all programs using it
   resize  resize a TOMB to a new size -s (can only grow)

   // Operations on keys:
   passwd  change the password of a KEY (needs old pass)
   setkey  change the KEY locking a TOMB (needs old key and pass)

   // Backup on paper:
   engrave makes a QR code of a KEY to be saved on paper

   // Steganography:
   bury    hide a KEY inside a JPEG image (for use with -k)
   exhume  extract a KEY from a JPEG image (prints to stdout)
   cloak   transform a KEY into a TEXT using CIPHER (for use with -k)
   uncloak extract a KEY from a TEXT file using CIPHER (prints to stdout)

  Options:

   -s     size of the tomb file when creating/resizing one (in MiB)
   -k     path to the key to be used ('-k -' to read from stdin)
   -n     don't process the hooks found in tomb
   -o     options passed to commands: open, lock, forge (see man)
   -f     force operation (i.e. open even if swap is active)
   -g     use a GnuPG key to encrypt a tomb key
   -r     provide GnuPG recipients (separated by comma)
   -R     provide GnuPG hidden recipients (separated by comma)
   --kdf  forge keys armored against dictionary attacks

   -h     print this help
   -v     print version, license and list of available ciphers
   -q     run quietly without printing informations
   -D     print debugging information at runtime

What is this for, exactly?

This tool can be used to dig .tomb files (LUKS volumes), forge keys protected by a password (GnuPG encryption) and use the keys to lock the tombs. Tombs are like single files whose contents are inaccessible in the absence of the key they were locked with and its password.

Once open, the tombs are just like normal folders and can contain different files, plus they offer advanced functionalities like bind and execution hooks and fast search, or they can be slammed close even if busy. Keys can be stored on separate media like USB sticks, NFC, on-line SSH servers or bluetooth devices to make the transport of data safer: one always needs both the tomb and the key, plus its password, to access it.

The tomb script takes care of several details to improve user's behaviour and the security of tombs in everyday usage: protects the typing of passwords from keyloggers, facilitates hiding keys inside images, indexes and search a tomb's contents, mounts directories in place, lists open tombs and selectively closes them, warns the user about free space and last time usage, etc.

How secure is this?

Death is the only sure thing in life. That said, Tomb is a pretty secure tool especially because it is kept minimal, its source is always open to review (even when installed) and its code is easy to read with a bit of shell script knowledge.

All encryption tools being used in Tomb are included as default in many GNU/Linux operating systems and therefore are regularly peer reviewed: we don't add anything else to them really, just a layer of usability.

The file KNOWN_BUGS.md contains some notes on known vulnerabilities and threat model analysis.

In absence or malfunction of the Tomb script it is always possible to access the contents of a Tomb only using a dm-crypt enabled Linux kernel, cryptsetup, GnuPG and any shell interpreter issuing the following commands as root:

lo=$(losetup -f)
losetup -f secret.tomb
gpg -d secret.key | head -c -1 | cryptsetup --key-file - luksOpen $lo secret
mount /dev/mapper/secret /mnt

One can change the last argument /mnt to where the Tomb has to be mounted and made accessible. To close the tomb then use:

umount /mnt
cryptsetup luksClose /dev/mapper/secret

Stage of development

Tomb is an evolution of the 'mknest' tool developed for the dyne:bolic 100% Free GNU/Linux distribution in 2001: its 'nesting' mechanism allowed the liveCD users to encrypt and make persistent home directories. Since then the same shell routines kept being maintained and used for dyne:bolic until 2007, when they were ported to work on more GNU/Linux distributions.

As of today, Tomb is a very stable tool also used in mission critical situations by a number of activists in dangerous zones. It has been reviewed by forensics analysts and it can be considered safe for adoption where the integrity of information stored depends on the user's behaviour and the strength of a standard AES-256 (XTS plain) encryption algorithm (current default) or, at one's option, other equivalent standards supported by the Linux kernel.

Compatibility

Tomb can be used in conjunction with some other software applications, some are developed by Dyne.org, but some also by third parties.

Included extra applications

These auxiliary applications are found in the extras/ subdirectory of distributed Tomb's sourcecode:

• GTomb is a graphical interface using zenity
• gtk-tray is a graphical tray icon for GTK panels
• qt-tray is a graphical tray icon for QT panels
• tomber is a wrapper to use Tomb in Python scripts
• docker is a wrapper to use Tomb through Docker

External applications

The following applications are not included in Tomb's distributed sourcecode, but are known and tested to be compatible with Tomb:

• Secrets is a software that can be operated on-line and on-site to split a Tomb key in shares to be distributed to peers: some of them have to agree to combine back the shares in order to retrieve the key.

• zuluCrypt is a graphical application to manage various types of encrypted volumes on GNU/Linux, among them also Tombs, written in C++.

• Mausoleum is a graphical interface to facilitate the creation and management of tombs, written in Python.

• pass-tomb is a console based wrapper of the excellent password keeping program pass that helps to keep the whole tree of password encrypted inside a tomb. It is written in Bash.

If you are writing a project supporting Tomb volumes or wrapping Tomb, let us know!

Compliancy

Tomb qualifies as sound for use on information rated as "top secret" when used on an underlying stack of carefully reviewed hardware (random number generator and other components) and software (Linux kernel build, crypto modules, device manager, compiler used to built, shell interpreter and packaged dependencies).

Tomb volumes are fully compliant with the FIPS 197 advanced encryption standard published by NIST and with the following industry standards:

• Information technology -- Security techniques -- Encryption algorithms
  • ISO/IEC 18033-1:2015 -- Part 1: General
  • ISO/IEC 18033-3:2010 -- Part 3: Block ciphers

Tomb implementation is known to address at least partially issues raised in:

• Information technology -- Security techniques -- Key management
  • ISO/IEC 11770-1:2010 -- Part 1: Framework
  • ISO/IEC 11770-2:2008 -- Part 2: Mechanisms using symmetric techniques
• ISO/IEC 27005:2011 Information technology -- Security techniques -- Information security risk management
• ISO/IEC 24759:2014 Information technology -- Security techniques -- Test requirements for cryptographic modules

Any help on further verification of compliancy is very welcome, as the access to ISO/IEC document is limited due to its expensive nature.

Use stable releases in production!

Anyone planning to use Tomb to store and access secrets should not use the latest development version in Git, but use instead the .tar.gz release on https://files.dyne.org/tomb . The stable version will always ensure backward compatibility with older tombs: we make sure it creates sane tombs and keys by running various tests before releasing it. The development version in Git might introduce sudden bugs and is not guaranteed to produce backward- or forward-compatible tombs and keys. The development version in Git should be used to report bugs, test new features and develop patches.

So be warned: do not use the latest Git version in production environments, but use a stable release versioned and packed as tarball on https://files.dyne.org/tomb

How can you help

Donations are very welcome, please go to https://www.dyne.org/donate

Translations are also welcome: they can be contributed editing sending the .po files in extras/translations.

The code is pretty short and readable. There is also a collection of specifications and design materials in the doc directory.

To contribute code and reviews visit https://github.com/dyne/Tomb

If you plan to commit code into Tomb, please keep in mind this is a minimalist tool and its code should be readable. Guidelines on the coding style are illustrated in doc/HACKING.txt.

Tomb's developers can be contacted using the issues on GitHub or over IRC on https://irc.dyne.org channel #dyne (or direct port 9999 SSL)

Licensing

Tomb is Copyright (C) 2007-2021 by the Dyne.org Foundation and maintained by Denis Roio J@dyne.org. More information on all the developers involved is found in the AUTHORS file.

This source code is free software; you can redistribute it and/or modify it under the terms of the GNU Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version.

This source code is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. Please refer to the GNU Public License for more details.

You should have received a copy of the GNU Public License along with this source code; if not, write to: Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.