Re: encrypted swap

[Pavel Machek]

Hi!

> > Now that laptop is stolen at an airport. The thief decides
> > to try to improve his take by grabbing useful information
> > from documents.  The encrypted documents are untouchable,
> > of course.  It _doesn't matter_ that the thief has the
> > hardware, the decryption key is protected by a passphrase
> > which is _nowhere_ on the hard drive.
> >
> > The only place that sensitive, unencrypted data could be
> > on such a machine is in swap.  In fact, it is _likely_ to
> > be in swap.
> >
> > Encrypted swap solves this _particular_ problem nicely,
> > does it not?
> 
> You got it bit.. wrong. Or, non-specific. If you assume that your laptop
> is stolen while its powered, then encrypted swap won't help you (strings
> /proc/kcore & the likes). If its going to be stolen while its offline, you
> can have your shutdown scripts blank the swap partition and the boot
> scripts call mkswap on it.
> 
> Or, somehow better & safer (or, explain the drawback):
> 
> spiral:~# dd if=/dev/zero of=/swap bs=1024k count=16
> 16+0 records in
> 16+0 records out
> spiral:~# losetup -e DES /dev/loop0 /swap
> Password:
> Init (up to 16 hex digits):
> spiral:~# mkswap /dev/loop0
> Setting up swapspace version 1, size = 16773120 bytes
> spiral:~# swapon /dev/loop0
> spiral:~# cat /proc/swaps
> Filename                        Type            Size    Used    Priority
> /dev/loop0                      partition       16376   0       -3
> 
> There, you have the swap encrypted, up and running. Of course, if
> you need

You have your swap encrypted, but I'm not sure for how long you'll see
it running before it deadlocks. Unless -e DES and loop were designed
for use with swap (were they?), this is tricky. Does anyone know if
swapping over loop is safe?

> more fancy encryption than the default, XOR or DES, get the crypto patch.
> You only need to have a script that does the stuff, that runs when the
> system boots, without shutdown scripts (in case of power/battery failure
> these might not be executed, hence the swap would not be wiped). Of
> course, you'll need to enter the losetup password upon booting, which
> might prove annoying (then again, if kernel would provide swap
> encryption, the only way to make it non-decryptable would be for you to
> enter a password, same drawback actually).

You could generate random password each boot. Should work well enough.

								Pavel
-- 
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