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

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

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 shared GNU/Linux components.

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

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

  Syntax: tomb [options] command [arguments]

  Commands:

   // Creation:
   dig     create a new empty TOMB file of size -s in MB
   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 specify KEY file)
   index   update the search indexes of tombs
   search  looks for filenames matching text patterns
   list    list of open TOMBs and information on them
   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 stout)

  Options:

   -s     size of the tomb file when creating/resizing one (in MB)
   -k     path to the key to be used ('-k -' to read from stdin)
   -n     don't process the hooks found in tomb
   -o     mount options used to open (default: rw,noatime,nodev)
   -f     force operation (i.e. even if swap is active)
   --kdf  generate passwords 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 symmetric 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, 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: secures the typing of passwords from keyloggers, facilitates hiding keys inside images, indexes and search a tomb's contents, 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=$(losetup -f)
losetup -f secret.tomb
pass="$(gpg -d secret.key)"
echo -n -e "$pass" | cryptsetup --key-file - luksOpen $lo secret
mount /dev/mapper/secret /mnt
unset pass

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 to be safe for military grade use where the integrity of information stored depends on the user's behaviour and the strength of a standard AES-256 (XTS plain) encryption algorithm.

Compliancy

Tomb volumes are fully compliant FIPS 197 and with:

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

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

• ISO/IEC 11770-1:2010 Information technology -- Security techniques -- Key management -- Part 1: Framework
• ISO/IEC 11770-2:2008 Information technology -- Security techniques -- Key management -- 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

As such Tomb qualifies 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).

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 needed: they can be contributed via this website https://poeditor.com/join/project/b276xMGAmB or simply sending the .po file. Start from extras/po/tomb.pot.

The code is pretty short and readable: start looking around and the materials found in doc/ which are good pointers at security measures to be further implemented.

For the bleeding edge 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) 2007-2017 by the Dyne.org Foundation

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.