RE: Bitlocker without PIN
- From: "John Lightfoot" <jlightfoot@xxxxxxxxx>
- Date: Thu, 24 Feb 2011 15:37:22 -0500
I agree that transparent Bitlocker is a great security tool.
Per, could you provide more details where you say:
"Using Passware Forensic Toolkit you can extract the bitlocker key using live memory dumping through Firewire (either by using an existing Firewire port, or by inserting an pcmcia/expresscard firewire card). No need to logon to Windows there..."
My understanding of the way Bitlocker works is that when you enable full-disk encryption, Bitlocker creates a small, unencrypted partition that contains the Windows login module. Once you've entered your credentials and they've been validated, the login module uses them to access the TPM for the key to decrypt the rest of the hard drive. I do not believe the encryption key is resident in memory until after the login credentials are verified, so I don't think the firewire hack or other memory scanning techniques would allow you to retrieve the key prior to authentication.
From: listbounce@xxxxxxxxxxxxxxxxx [mailto:listbounce@xxxxxxxxxxxxxxxxx] On Behalf Of Thor (Hammer of God)
Sent: Thursday, February 24, 2011 12:07 PM
To: Per Thorsheim; focus-ms
Subject: RE: Bitlocker without PIN
I don't agree with blanket statements like "is not a good idea in terms of security."
I'm willing to wager that insofar as "real world" application of security is concerned, that most people on this list are not designing solutions around what keys can be extracted from live memory via firewire. Sure, it's cool, and l337, and provides for jazz-hand presentation content, but it is not the use-case that we are solving for. If it is, then additional mechanisms should be employed.
Security is about risk mitigation - as such, transparent TPM-based Bitlocker can be an absolutely fantastic security control. It can be seamlessly rolled out, controlled by group policy, and data can be protected by way of recover agents. It provides disk encryption without requiring the user to remember PINs, etc. Sure, PINs are better as I stated in my last email, but they require more administration. This solves for the 90th percentile (if not more) of the cases I've seen where the asset is lost or stolen.
I have to reply like this because it would be a real shame if people saw the "not good for security" post and figured "ah, screw it then" and moved on. We should solve for reasonable use cases appropriately in cost effective ways that reduce administration where possible. Sure, they can extract keys from live memory via firewire - - and I can extract PINs from live people with a box cutter. I think you see where I'm going with this...
From a security standpoint, transparent bitlocker is a fantastic feature. PINs are better. Everything should be put in proper perspective.
From: listbounce@xxxxxxxxxxxxxxxxx [mailto:listbounce@xxxxxxxxxxxxxxxxx] On Behalf Of Per Thorsheim
Sent: Thursday, February 24, 2011 1:35 AM
Subject: RE: Bitlocker without PIN
"Transparent" Bitlocker with TPM and direct boot to Windows Logon is not a good idea in terms of security.
At the Passwords^10 conference in Dec 2010, Passware revealed their newest versio of their forensic toolkit. You probably want to see that:
Using Passware Forensic Toolkit you can extract the bitlocker key using live memory dumping through Firewire (either by using an existing Firewire port, or by inserting an pcmcia/expresscard firewire card). No need to logon to Windows there...
Depending on your configuration, the hibernation file may be unencrypted. This can then be extracted from the disk and analyzed to get the bitlocker decryption key as well.
1. Superglue for your Firewire and pcmcia/expresscard ports 2. Do not allow hibernation mode OR encrypt the hibernation file as well 3. Always use Pre-Boot Authentication (PBA) in some form (pin, password,
On Wed, 2011-02-23 at 21:45 +0000, Alexander Kurt Keller wrote:
Speaking as an individual and not representing my institution. If you can handle the support overhead I would require the PIN or physical key in addition to the transparent TPM key for added protection.
Re: What happens if he boots with a linux live CD/USB? Can he decrypt the drive? The key is stored in the TPM. Does linux have access to the TPM?
No. This is not a viable attack, these links explain in a nutshell how TPM works:
There are a number of viable attacks (and plenty more theoretical attacks) against all types of full drive encryption, including BitLocker, but it is not as trivial as using a Linux bootdisk.
Re: We are just not sure if the extra security worths having the users to type 2 passwords to boot a laptop.
If the attacker can gain physical access to the computer, and it uses TPM and boots straight to Windows, then they could attack the computer at the network layer and at the console, or via one of the more advanced hardware attacks (chip cooling, hibernation file excavation, etc.). Requiring a PIN at boot adds an extra layer of protection before the OS starts.
It comes down to a risk analysis of your environment and what you are trying to protect. For my laptop I use TrueCrypt (which by design requires a PIN) because it is a transient computer at risk for theft and contains information that could be leveraged in an attack against our infrastructure. Furthermore I use KeePass to encrypt all passwords, and AxCrypt for all sensitive documents, which offers a second layer of protection should the computer be compromised while it is booted.
It should be pointed out that BitLocker/TrueCrypt/EFS/etc. will do little or nothing to stop an attack inbound from the network or malicious code that has been allowed to execute on the running OS.
Academic Technology, San Francisco State University
Office: Burk Hall 153 Phone: (415)338-6117 Email: alkeller@xxxxxxxx
[mailto:listbounce@xxxxxxxxxxxxxxxxx] On Behalf Of Shang Tsung
Sent: Thursday, February 17, 2011 3:07 AM
Subject: Bitlocker without PIN
We are on the process of setting up Bitlocker on our laptops for OS encryption and we are wandering if we should set up a PIN or not. If we do not, the attacker can get to Windows login screen, but this is where he will stop.
What happens if he boots with a linux live CD/USB? Can he decrypt the drive? The key is stored in the TPM. Does linux have access to the TPM?
We are just not sure if the extra security worths having the users to type 2 passwords to boot a laptop.
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