RE: Bitlocker without PIN

Shang,

Your question has triggered a healthy discussion.  I want to start by sayin=
g that I work for Microsoft.  I am by no means an experienced security anal=
yst, I am a Technical Professional that has had numerous conversations with=
 customers and partners around disk encryption.  Let me start by directly a=
nswering your questions:

First, let us assume we are protecting our data from a thief who is going t=
o steal our laptop.  In my mind, it's very important that we focus on the t=
ype of threat we are trying to mitigate.  More on this below...

1.> We are on the process of setting up Bitlocker on our laptops for OS enc=
ryption 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 s=
top.

You are correct, BitLocker is designed to protect your OS and data from off=
line attacks when it is implemented properly.  Once Windows is up and runni=
ng, BitLocker does not do anything to protect the computer from network or =
user based attacks.  Once Windows has booted, Windows trusts the password c=
omplexity to prevent the thief from logging into Windows.  Any user that ha=
s a valid username and password will have access to the BitLocker encrypted=
 OS and data.  Again, BitLocker is to prevent offline attacks. =20
=20
2.> What happens if he boots with a linux live CD/USB? Can he decrypt the d=
rive? The key is stored in the TPM. Does linux have access to the TPM?

This is the offline attack scenario, and right up BitLockers alley!  The dr=
ives protected with BitLocker are encrypted on the disk.  Any other OS inst=
ance (including other Windows installations) can see the BitLocker partitio=
ns, but they are unreadable.  These other OS instances "see" these partitio=
ns as either 1) encrypted partitions 2) unusable partitions, or 3) unused s=
pace.   Another OS could delete or reformat BitLocker volumes.
The value TPM brings is that the TPM chip "uniquely pairs" to your unique i=
nstallation of Windows.  If the user boots from any other OS, even another =
copy of Windows, that "other instance" is foreign to the TPM; hence the TPM=
 will not share the information that is needed to read the BitLockered driv=
e(s).  TPM is built to do a very good job of resisting TPM based attacks, b=
ut without implementing a PIN in combination with BitLocker, all of the inf=
ormation needed to access the encrypted partitions is within the confines o=
f our laptop.  Given enough time and enough resources, the thief *may* be a=
ble to eventually access the data on the computer.  Adding the PIN increase=
s the time and resources required to compromise the BitLocker volumes. =20
I agree with Thor, I do not deal in absolutes.  If someone has access to a =
physical resource and enough resources and desire, most likely they will ev=
entually be able to access your encrypted data.  From everything I've seen,=
 BitLocker with a PIN usually requires years of energy to compromise the en=
crypted data.  The PIN requirement prevents Windows from booting until the =
proper PIN is entereed.  This PIN is also needed to access the encrypted vo=
lumes.  The PIN requirement provides a very high level of confidence that y=
our data will not be compromised, but again, this is not an absolute!

I view the PIN as a tool that will prevent an attacker from repeatedly boot=
ing the OS in an effort to try and extract the BitLocker key using a tool l=
ike the Passware Forensic Toolkit, or chip cooling.  Without the correct PI=
N, the OS will not boot, hence the OS will not "contain" the BitLocker key =
to be harvested.


3.> We are just not sure if the extra security worths having the users to t=
ype 2 passwords to boot a laptop.

This is a business decision.  As Thor said, BitLocker without a PIN does a =
very good job of protecting your data in the event of a loss from the major=
ity of the people trying to steal a computer for the value of the computer.=
  For the typical thief, BitLocker without a PIN *may* be good enough.  For=
 those people that are determined to steal your computer for the value of t=
he data, and have the time and resources to do so, they will most likely ev=
entually be able access your data.  Encryption is a time vs. value of data =
discussion.  In my opinion, the goal with encryption is to drive the "time"=
 required to access your data high enough that your data is "not that valua=
ble".=20


What type of "thief" are you protecting your data from? =20
1. Accidental computer loss?  --  The PIN *may* not be necessary,
2. Intentional theft by a professional thief who is trying to harvest your =
data for the value of the data?  --  I think you should do everything you c=
an to protect your data.  In my mind, a PIN is a requirement! =20

What about standby and hibernate?  -- If you deploy BitLocker properly, enc=
rypt your OS volume and your data volumes, hibernate is still able to be us=
ed since the hibernate file will be written (by default) to your OS (encryp=
ted) drive.  When you resume from hibernate, you will have to enter your PI=
N.  Standby on the otherhand does not require PIN entry.  Someone that acqu=
ires a machine in standby has the benefit of having a computer that has alr=
eady passed the pre-boot PIN requirement.  There is a very good best practi=
ces document here:
http://technet.microsoft.com/en-us/library/dd875532(WS.10).aspx
This document talks about disabling standby on BitLocker enabled machines. =
 Disabling standby means that the user can either hibernate Windows, or shu=
t it down.  Either way, a PIN will be required upon reboot or resume from h=
ibernate. =20
This URL also talks about setting group policies so that the BitLocker reco=
very key is always uploaded to AD.  This way if the user forgets their PIN =
or corrupts their OS installation, the Domain Administrator can leverage th=
is recovery key to access and recover the user data from the BitLockered dr=
ive(s). =20

There is also a good document that discusses BitLocker vs. EFS.
http://technet.microsoft.com/en-us/library/cc162807.aspx

While these documents make mention of Windows Vista in places, please know =
that BitLocker for Windows 7 is a superset of BitLocker in Windows Vista.  =
Windows 7 also gives you the ability to use "BitLocker to go" for removable=
 drives.  You can set a policy that your computer is not allowed to write t=
o a removable drive unless it is encrypted.  By forcing BitLocker to go, yo=
u can ensure your users don't put critical data on unencrypted removable me=
dia.

I've blogged about the encryption offered in Windows.  Please feel free to =
check out these blog entries, they may help explain some of the details.
http://blogs.technet.com/b/uspartner_ts2team/archive/2010/03/17/what-is-bit=
locker-what-does-it-do-what-does-it-not-do.aspx
I've also blogged about other forms of encryption Windows can natively take=
 advantage of here:
http://blogs.technet.com/b/uspartner_ts2team/archive/2010/03/18/other-forms=
-of-encryption-you-need-to-consider.aspx


I'm required to say that while I feel the information I've provided is acur=
ate, my responses are my opinion and not necessarily the views of Microsoft=
. =20

I hope this helps...

________________________________________
From: [email protected] [[email protected]] on behalf=
 of Thor (Hammer of God) [[email protected]]
Sent: Thursday, February 24, 2011 11:07 AM
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 i=
s concerned, that most people on this list are not designing solutions arou=
nd what keys can be extracted from live memory via firewire.  Sure, it's co=
ol, and l337, and provides for jazz-hand presentation content, but it is no=
t the use-case that we are solving for.  If it is, then additional mechanis=
ms should be employed.

Security is about risk mitigation - as such, transparent TPM-based Bitlocke=
r can be an absolutely fantastic security control.  It can be seamlessly ro=
lled out, controlled by group policy, and data can be protected by way of r=
ecover agents.  It provides disk encryption without requiring the user to r=
emember 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 th=
e "not good for security" post and figured "ah, screw it then" and moved on=
.   We should solve for reasonable use cases appropriately in cost effectiv=
e ways that reduce administration where possible.  Sure, they can extract k=
eys from live memory via firewire - - and I can extract PINs from live peop=
le 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.

t

-----Original Message-----
From: [email protected] [mailto:[email protected]] On=
 Behalf Of Per Thorsheim
Sent: Thursday, February 24, 2011 1:35 AM
To: focus-ms
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:
ftp://ftp.ii.uib.no/pub/passwords10/

Using Passware Forensic Toolkit you can extract the bitlocker key using liv=
e memory dumping through Firewire (either by using an existing Firewire por=
t, or by inserting an pcmcia/expresscard firewire card). No need to logon t=
o Windows there...

Depending on your configuration, the hibernation file may be unencrypted. T=
his can then be extracted from the disk and analyzed to get the bitlocker d=
ecryption key as well.

Lessons learned:
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,
smartcard..)

--
Best regards,
Per Thorsheim
securitynirvana.blogspot.com




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 add=
ition 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 TP=
M works:
> http://windows.microsoft.com/en-US/windows-vista/BitLocker-Drive-Encry
> ption-Overview
> http://geekswithblogs.net/sdorman/archive/2006/07/04/84045.aspx
>
> There are a number of viable attacks (and plenty more theoretical attacks=
) against all types of full drive encryption, including BitLocker, but it i=
s 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 try=
ing to protect. For my laptop I use TrueCrypt (which by design requires a P=
IN) because it is a transient computer at risk for theft and contains infor=
mation that could be leveraged in an attack against our infrastructure. Fur=
thermore I use KeePass to encrypt all passwords, and AxCrypt for all sensit=
ive documents, which offers a second layer of protection should the compute=
r 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 th=
at has been allowed to execute on the running OS.
>
> Best,
> alex
>
>
> Alex Keller
> Systems Administrator
> Academic Technology, San Francisco State University
> Office: Burk Hall 153 Phone: (415)338-6117 Email: [email protected]
>
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Shang Tsung
> Sent: Thursday, February 17, 2011 3:07 AM
> To: [email protected]
> Subject: Bitlocker without PIN
>
> Hello all,
>
> We are on the process of setting up Bitlocker on our laptops for OS encry=
ption 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 sto=
p.
>
> What happens if he boots with a linux live CD/USB? Can he decrypt the dri=
ve? 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 typ=
e 2 passwords to boot a laptop.
>
> ST=