[dm-crypt] luksSuspend

Arno Wagner arno at wagner.name
Thu Jan 27 12:02:08 CET 2011


On Thu, Jan 27, 2011 at 03:35:26AM -0500, Navix wrote:
> I have an alarm system that runs a script and I'm looking for the quickest
> method to clear the encryption keys from the RAM to prevent cold boot
> attacks. 
> The server has two RAID 0 arrays assume "ARRAY0" is the boot drive
> that is encrypted and contains Ubuntu 10.04, the cryptsetup binary is on
> this array. The other array "ARRAY1" is a storage array that is also
> encrypted. Will running the commands below clear the encryption keys from
> the RAM even tough the cryptsetup binary is on the encrypted array that will
> be suspended and is there a better method for doing this? Also do these
> commands clear the write buffer for the hard drive or could some data be
> lost?
> 
> cryptsetup luksSuspend ARRAY1
> cryptsetup luksSuspend ARRAY0

Have you looked at the man-page of cryptsetup? There is a clear 
warning:

    WARNING:  never  try  to  suspend device where is the cryptsetup
              binary itself.

I would suggest that your project is not well-researched at this 
time.

Also accordiong to the man-page, all IO is frozen immediately,
which means all data in buffer is lost, unless you luksResume
later. This is correct behaviour. Flushing can take arbitrarily
long, especially if an application is writing data. If you want
a working slush, I suggest you umount the devices before issuing
the luskSuspend. You will find thid rather difficult with
the root filesystem, so you could try a remount to ro (read-0only)
here. This may still fail or block.

What I would suggest, is to put a statically compiled copy of 
the cryptsetup binary onto a ram-disk and run it from there.

What you should do in any case before continuing, is to 
clearly state your security goals and their priority 
level compared to operational considerations, like 
preventing data loss and corruption. These priorities 
will have a huge impact on the solution. 

Also, you should think about your sensor design. A cold-boot
attack willt ypically just issue a hardware reset, and
there is no way to prevent this on the x86 platform.

Arno


-- 
Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno at wagner.name 
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