BestCrypt: Cross-Platform Filesystem Encryption

This month Mick reviews BestCrypt, an open-source application that allows you to share encrypted volumes between Windows and Linux systems.
Installing BestCrypt from Source-RPM

Once your kernel source is in place and its dependencies built, you can build and install BestCrypt. If you use an RPM-based Linux distribution, get the source RPM (as of this writing the current one is BestCrypt-1.0b-5.src.rpm) and build it with the --rebuild flag:

rpm --rebuild ./BestCrypt-1.0b-5.src.rpm

This will build a binary package of BestCrypt in either /usr/src/redhat/RPMS/i386 (on Red Hat systems) or /usr/src/packages/RPMS/i386 (on SuSE and probably others too). You can then install that package like you would any other, for example:

rpm -Uvh /usr/src/packages/RPMS/i386/
    BestCrypt-1.0b-5.i386.rpm
After BestCrypt's binaries and READMEs are in place, the RPM's post-installation script will load BestCrypt's kernel modules. You're now ready to use BestCrypt.

Installing BestCrypt from Source Tarball

If you use a non-RPM-based distribution such as Debian or Slackware, download the tarball instead of the source RPM (the most current one at the time of this writing is BestCrypt-1.0b-5.tar.gz). Unpack it in /usr/src, change your working directory to /usr/src/bcrypt and do a make && make install. If your kernel source is set up correctly, BestCrypt should compile and install without errors.

The tarball's Makefile, however, isn't quite as sophisticated as the RPM installation scripts. You'll need to load BestCrypt's modules manually before using BestCrypt for the first time. The simple way to do this is with BestCrypt's startup script, e.g., /etc/init.d/bcrypt start.

BestCrypt's Documentation and Control Panel

In addition to BestCrypt itself, you should download the documentation tarball too. This contains a directory providing BestCrypt's documentation in the form of HTML pages (Figure 1).

Figure 1. BestCrypt's Documentation

Another thing you may want is BC_Panel, the BestCrypt Control Panel. This is available only in the form of a binary RPM (though it may be installable under Debian using alien). BC_Panel provides a GUI for BestCrypt that very closely resembles BestCrypt's Windows GUI.

Since the current version of BC_Panel as of this writing is 0.2-1, and since it doesn't appear to support all the features of the command-line version (or of the Windows GUI), BC_Panel appears to be a work-in-progress. Still, it's useful for some things and appears to be stable.

Using BestCrypt for Linux

Creating a BestCrypt container is quick and easy. Here is a sample session:

bctool new myvault.jbc -s 150M -a twofish
-d "my test vault"
  Enter password:
  Verify password:

BestCrypt has one main command-line tool, bctool. To create a new container you simply send bctool the command new followed by the container's filename, size, encryption algorithm and description. BestCrypt then prompts you for a password.

Make sure to use a strong password. Although all of BestCrypt's supported algorithms except DES use 128-bit or greater keys to encrypt containers, a container's key is itself hashed with your password. An easily guessed password means an easily decrypted container, no matter how big of a key it was encrypted with.

Make sure also to write down your password and keep it in a safe place, or choose a password you're positive you won't forget; according to Jetico, passwords are absolutely nonrecoverable, and there are no backdoors in BestCrypt for password recovery. This is very much a positive thing: while it means you will lose data irretrievably should you forget or lose your password, it also means the only way for an attacker to decrypt your container is to guess or brute-force your password.

After creating a container, you need to create a filesystem in it. This is done with bctool's format command:

bctool format -t msdos ./myvault.jbc

Use the -t flag to specify a filesystem format supported by your system. If you're going to share this container with the Windows version of BestCrypt, be sure to specify msdos (if you actually use the vfat long filename extensions, aka Windows 95 long filenames, you should still format the container as msdos, and then mount it as vfat). BestCrypt can format containers in all file formats supported by your system.

To Root or Not to Root?

Once a BestCrypt container has been created and formatted, it can be mounted. The command syntax to do so is very similar to that of the familiar mount command:

bctool mount -t vfat ./myvault.jbc ./mnt/kraunj00lz

From this point on (until you dismount the volume) the volume may be accessed like any other directory. By default, the volume's user and group will be set to those of the user who mounted it, with permissions set to 0700 (drwx------). In other words, other (non-root) users won't be able to access your volume unless you intentionally mount it with different ownership or permissions. You can specify a different user, group and permission mode at mount time with bctool's -o, -g and -m flags, respectively. See the bctool(8) man page for details and examples.

When you're done using the BestCrypt container, you can unmount it like this:

bctool umount ./mnt/kraunj00lz

While a BestCrypt container is unmounted, it can be backed up, copied and otherwise treated like any other file. While it's mounted, though, it can't be changed or manipulated (except by bctool).

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