| Editorials
@ Applelust |
| Panther
In Depth: FileVault: A Secure Image |
© 10-27-03
András Puiz
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What good is all that great Unix security if there
are dead easy ways to go around it? Your home folder
may be unaccessible for other users of the same machine
or network, but if your Mac is still capable of booting
into OS 9, that system will happily reveal all folders
and files, ignorant of access privileges. But even
if your computer is OS X-only, that's still not a
reason to feel secure about your data: thieves can
put your Mac in Target Disk Mode and see all your
files on a Mac running OS 9, or simply remove your
hard disk and insert it into an older Mac that will
show it all. (That should make Macs capable of running
OS 9 a great commodity among data thieves for years
to come…)
Security experts agree that most security measures
are futile once someone has physical access to your
computer. Once your laptop is stolen, or your desktop
is in the hands of a tech-savy burglar, your privileged
data will no longer be privileged: by using the means
described above, your credit card numbers, mailboxes,
classified documents and access privileges to secure
websites may easily be taken advantage of. This is
bad news (and old news) for people who store sensitive
content on their computers, but with Panther, it's
about to change.
Destruction of your data is still impossible to prevent:
erasing a hard disk will always do the trick, but
dipping your PowerBook into hot lava will most probably
also adversely affect the data stored on the machine
(though Applelust hasn't been able to fully verify
this allegation yet). But if you're worried that your
data would ever get into the wrong hands, worry no
more: enter FileVault, a clever, ingenious way to
secure your home folder by encrypting it using the
Advanced
Encryption Standard (AES) 128-bit encryption,
keeping it totally unintelligible and unpenetrable
to prying eyes. How secure is that? According to the
National
Institute of Standards and Technology, it's pretty
secure:
Assuming that one could build a machine that could
recover a DES key in a second (i.e., try 255
keys per second), then it would take that machine
approximately 149 thousand-billion (149 trillion)
years to crack a 128-bit AES key. To put that into
perspective, the universe is believed to be less
than 20 billion years old.
The Details
Here's what FileVault does. If you choose to enable
it, the contents of your home folder (your Library,
containing your applications' preferences; your Documents
folder, your Desktop, as well as your Movies, Pictures
and Music folders, and whatever else you store under
your user folder) will be moved into an encrypted
disk image. And that's it. FileVault will use your
account's login password to encrypt and decrypt your
data, so make sure you choose a strong enough (i.e.
hard to guess) password. But be careful: should you
forget that password, there'll be no way in hell to
get your data back! (As a "safety net" measure,
you can set a master password for your entire computer
that will let you decrypt any user's FileVault. Use
this master password with care, though, and make sure
it won't defeat the purpose of your FileVault.)
With FileVault active, any read/write operations
will perform the necessary encryption/decryption on
the fly. This is totally transparent for the user,
but naturally, comes with a performance penalty. In
the few tests I've performed, I've discovered that
copying a large file to an encrypted home folder took,
on the average, almost twice as long as copying the
same file to an unprotected location, with all other
circumstances being equal. This may be quite significant
for some hard disk-intensive uses, like movie rendering,
but we'll have to see experts confirming this before
jumping to conclusions. With the exception of disk-intensive
tasks, the system didn't seem any slower with FileVault
turned on.
You activate FileVault in the Security pane of the
System Preferences application. If you enable it,
the system will log you out, and spend considerable
time moving the contents of your home folder into
the encrypted disk image. After that, you'll be able
to log back in. Your home folder will be kept and
renamed as an empty placeholder, but your real files
will be kept in a secure disk image.
 |
| The Security
Control Panel, where FileVault is controlled. |
Is It For You?
Who should use FileVault? Turning it on is no big
deal, and the performance hit you get with it may
not be that great. Yet it may be unnecessary overkill
for many users. You should definitely consider using
FileVault if you have sensitive data on your computer
that could cause great harm to you (or others) if
it falls into the wrong hands. If you feel you may
not be able to prevent malicious physical access to
your Mac (for example, you are a laptop user), that's
another reason to be extra careful. In that case,
you should definitely use the other security features
as well. Disabling automatic login is a necessary
step, or else your secured home folder may automatically
surrender to anyone restarting your Mac. If you fear
that the security of your Mac may be compromised while
it's in use, consider password-protecting your screen
saver and sleep mode, and maybe even automatically
logging out after a set time. These options can all
be set in the Security pane of System Preferences.
Alternatives and Workarounds
If you're suffering from the performance penalty
caused by FileVault, and don't want to secure all
your files, you can always work outside your home
folder, and maybe move those files into your secured
home later. But if you don't think that all your data
(including application preferences, bookmarks, etc.)
need to be secured, only a few classified documents,
you can skip FileVault and create your own secure
location anywhere. All you need to do is launch Disk
Utility from the Utilities folder (within the Applications
folder), and create an AES-128-encrypted disk image.
You'll need to specify a password (that will be stored
in your Keychain if you agree to that), and there,
you'll have your own miniature FileVault.
It will be a disk image you can mount using that
password, and use it as a separate volume unti you
eject it (at which point, its contents will be stored
in the Disk Image file). This image will be fixed-size,
unlike the FileVault, which Mac OS X keeps always
at the right size, offering to resize it each time
you log out. Note, though, that just like the "real"
FileVault, the DIY version will be easily broken into
as well if you keep logged in with you Keychain unlocked
– just like no real-life vault is secure enough
if you leave the key in its door.
