> -----Original Message-----
> From: owner-cryptogra...@metzdowd.com [mailto:owner-
> cryptogra...@metzdowd.com] On Behalf Of Perry E. Metzger
> Sent: Friday, October 08, 2010 3:28 PM
> To: cryptography@metzdowd.com
> Subject: Disk encryption advice...
> I have a client with the following problem. They would like to encrypt all of
> their Windows workstation drives, but if they do that, the machines require
> manual intervention to enter a key on every reboot. Why is this a problem?
> Because installations and upgrades of many kinds of Windows software
> require multiple reboots, and they don't want to have to manually intervene
> on every machine in their buildings in order to push out software and
> patches.
> (The general threat model in question is reasonably sane -- they would like
> drives to be "harmless" when machines are disposed of or if they're stolen
> by ordinary thieves, but on the network and available for administration the
> rest of the time.)
> Does anyone have a reasonable solution for this?
> --
> Perry E. Metzger              pe...@piermont.com

This is a fairly well known problem for which many vendors have solutions of 
varying quality. I'll summarize a few approaches.

In general you want to have the window between the time a pre-boot 
authentication (PBA) bypass is set and the time of the reboot that consumes the 
bypass be as small as possible. Alternatively (my preferred) you want to have a 
pre-boot environment that can make a secure check to see if it is still on a 
safe/secured network and if it is, bypass PBA. This way PBA is bypassed any 
time the system is in a safe facility.

1) Some type of bypass file placed by the managing system that, if present on 
reboot tells the system to bypass the pre-boot authentication. The file should 
be settable only through an administrative function configured on management 
consoles, not locally. Ideally it should be protected by some crypto scheme. 
Checkpoint, McAfee, PGP for sure have this feature, but I believe most big 
vendor-owned solutions have it. I don't much care for *how* they implement it. 
PGP has a command-line command that sets the reboot flag, so a simple 
administrative-level cmd script can do it. The file may have a counter that is 
decremented (Checkpoint does) or it may need to be reset each time. I recommend 
that you deploy the bypass file as part of the patching process so the window 
is small as possible with only the known number of required reboots allowed.

2) Some systems can be configured to boot to Windows, and use Windows' IP stack 
to check for some conditions on the network. If the conditions are met, the 
system stays at the Windows prompt; if the conditions are not the system 
insitigates PBA and shuts down. On next boot it will be at the PBA prompt. I 
know of some vendors that do this, but do it really naively. One actually does 
nothing more than ping a series of IP addresses and if *any* of them respond 
they assume they are on the right network. Yes, they pin their network location 
awareness on the fact that nobody could ever think to spoof an ICMP echo 
response. I discourage this mode in general, even if done well because it 
depends on a fully booted windows box before it can check. I configured a small 
lab network to trivially bypass the ping test.

3) There is one vendor that has worked on this problem very hard over the last 
couple years to leverage vPro and Intel's secure wake-on-lan, and pre-boot 
environment to provide secure challenge-response based network awareness. If 
they determine they are on a secure network, they will continue past the boot 
prompt and if they determine they are not they'll either sit at the prompt or 
shut down. Oddly enough that company, McAfee, was recently bought by Intel. 
McAfee's leveraging of Intel's on-board security hardware was the main deciding 
factor in that purchase, or so I believe.

Disclaimer: My company isn't a McAfee disk encryption customer. I don't work 
for either company. I just happen to have dug pretty deeply into disk 
encryption companies and products over the last couple years and my opinion is 
that McAfee did it right and the others are playing catch up.

Off topic rant: None of the other security vendors seemed the least bit 
interested in the on-board security features Intel was building into systems, 
largely because if vendors built product around it, it might make them too 
interchangeable; replaceable. McAfee was different. Intel got tired of waiting 
for vendors to kick-start their products, so Intel bought the company that had 
gotten the furthest with Intel's tools. Personally, I'd hate to be competing 
with Intel/McAfee on the disk encryption or systems management front right now. 
Of course, they've still got plenty of latitude to screw it all up.

Eric Lengvenis
InfoSec Arch., VP

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