Encrypted filesystems

[kentborg at borg.org (Kent Borg)]

On Sun, Apr 24, 2005 at 02:41:43AM -0400, David Kramer wrote:
> Who has had positive experience with one of these?  

I periodically want to encrypt all hell out of everything (boot
partitions, data partitions, swap space, suspend-to-disk data, etc.),
I then investigate my options, and don't like what I find.  You have
me looking again, at least at this smaller problem.

This seems to work for me to have a single encrypted file-based
partition:

  $ dd if=/dev/urandom of=file bs=1024k count=10
  # losetup -e aes-256 /dev/loop0 file
  Password:
  # mkfs -t ext3 /dev/loop0
  # losetup -d /dev/loop0
  # mount -o encryption=aes-256 file /mnt/loop/
  Password:

But it likely requires the kernel compile you want to avoid.

> I'm looking into this for two reasons.  I would like to have
> encrypted content on my server,

Why?  If you want to protect against someone with physical or root
access to your server, an encrypted partition will help you the first
time the bad guy gets in, but if the bad guy starts logging what you
do s/he can get your passphrase the next time you type it.  Or access
your data next time you mount it.

> and I would like to have encrypted content on my USB pen drive
> (Sandisk 1GB).

Handy if you only type your passphrase on a keyboard and computer you
trust isn't spying on you.

Encrypting data on a notebook or thumb drive will keep the guy who
steals it from getting at the data--assuming you don't sleep your
notebook with the encrypted partition mounted.  If someone sneaks some
spyware onto your notebook while you aren't looking the same keystroke
logging will bust you then.  (Or, the root kit can just quietly grab
contents next time you mount it.)

If the bad guy gets a copy of your encrypted data (and is motivated
and skilled), will you have a strong enough passphrase?  These days a
passphrase with fewer than 90-bits worth of entropy in it is not good
enough against a motivated foe with resources (say, if the Feds think
you know where Bin Laden is).  In my above example I did a passphrase
with about 74-bits of entropy in it and it is long (4 randomly chosen
english words plus 8 randomly chosen hex characters), I don't have it
memorized yet, and once I do remember it, if I don't use it often, I
will forget it.

And what happens the day you are pulled aside at customs or airport
security and are ordered to type in your passphrase?  What do you do?
Do you care if they see your data?  (How much do you care?)


Finally, worry about corruption.  Munge a few bytes in your encrypted
file, the unencrypted changes will spray all over the place, and fsck
will not be able to help you.


That said, go for it.  If you are entrusted with the personal data of
others, definitely encrypt it.


-kb, the Kent who can frequently point out the dark side.