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Extracting Bitlocker Keys from a TPM

pulsesecurity.co.nz

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Re: Extracting Bitlocker Keys from a TPM

#21

Post by gtsteve »

Given Microsoft's response, it seems this isn't new. I'm in charge of my company's security so now I'm a bit concerned. I mandated the use of Bitlocker with TPM across the business but no pre-authentication measures.

How accessible is this attack to the common person? Note that I am concerned about curious thieves as opposed to three letter agencies. I believe I would still be correct in saying that it's still really hard for your average person to extract data from a plain-TPM encrypted Bitlocker.

Are there commercially available TPM adapters that make the attachment easier for example? It looks like their attachment technique could be refined with custom hardware.

It is troubling to see that Bitlocker+TPM is essentially just obfuscation though.

Re: Extracting Bitlocker Keys from a TPM

#22

Post by thisacctforreal »

close04 wrote: post #18
mjg59 wrote: post #17

Earlier quoted context omitted.

The described attack allows you to recover Bitlocker keys and decrypt the harddrive from any random computer that you have physical access to, since when you boot it the key will be sent over the LPC bus in a way that can be extracted. I'm not sure what the distinction you're making is, given that the probability that someone ends up with access to a TPM but not the system it's associated with is basically zero.

> This post will look at extracting the clear-text key from a TPM chip by sniffing the LPC bus It is a very interesting read but the title is a bit clickbaity. Luckily it's not with bad intentions, the first few lines (above) already tell you what it is. > I'm not sure what the distinction you're making is Imagine I tell you I can extract any information I want from the human brain. You'd be intrigued, how do I inter…

Honestly it feels like splitting hairs, unless I'm misunderstanding something.

What is there to gain "cracking" the TPM itself, if you can get the keys fine by sniffing?

Apple's Secure Enclaves aren't vulnerable to sniffing, as the AES keys used for encryption live only in silicon, with access to use them granted to the Enclave.

The keys never exist in a software-readable form, even to the coveted Enclave firmware. Do TPMs offer this functionality, and Bitlocker needs to take advantage of it? Or do TPMs just not protect their keys against physical access?

Re: Extracting Bitlocker Keys from a TPM

#23

Post by crote »

gtsteve wrote: post #21

Given Microsoft's response, it seems this isn't new. I'm in charge of my company's security so now I'm a bit concerned. I mandated the use of Bitlocker with TPM across the business but no pre-authentication measures. How accessible is this attack to the common person? Note that I am concerned about curious thieves as opposed to three letter agencies. I believe I would still be correct in saying that it's still really…

You're probably fine. Adapters do exist which make this a bit easier, but it's still going to be at least $100 in custom hardware. A curious thief is not going to bother with this and will just wipe the disk when they notice it's encrypted.

About difficulty: Given this article, I'd expect that most serious electronics hobbyists can currently do this. It's certainly not easy, but not that hard either. It wouldn't be too hard to turn this into a tool which can be used by anyone with a screwdriver, like what happened with the iPhone [0]. But again, why would a common thief bother to do this?

[0]: http://www.iphonehacks.com/2015/03/this-tiny-box-uses-brute-...

Re: Extracting Bitlocker Keys from a TPM

#24

Post by tallanvor »

gtsteve wrote: post #21

Given Microsoft's response, it seems this isn't new. I'm in charge of my company's security so now I'm a bit concerned. I mandated the use of Bitlocker with TPM across the business but no pre-authentication measures. How accessible is this attack to the common person? Note that I am concerned about curious thieves as opposed to three letter agencies. I believe I would still be correct in saying that it's still really…

The Bitlocker + TPM without PIN model is primarily aimed at preventing the contents of a drive from being accessed from a different system - you can send your old drive to the recycler without worrying about someone hooking it up to a different computer to scan for financial information or passwords.

For businesses that need to protect internal or customer data, the correct answer is requiring a PIN on boot, as this prevents the TPM from sending the key without receiving the PIN.

And it really shouldn't be surprising that if a computer doesn't require any user interaction before decrypting a drive that retrieving the encryption key is going to be relatively trivial if you're willing to put in some time and money.

Re: Extracting Bitlocker Keys from a TPM

#25

Post by rficcaglia »

gtsteve wrote: post #21

Given Microsoft's response, it seems this isn't new. I'm in charge of my company's security so now I'm a bit concerned. I mandated the use of Bitlocker with TPM across the business but no pre-authentication measures. How accessible is this attack to the common person? Note that I am concerned about curious thieves as opposed to three letter agencies. I believe I would still be correct in saying that it's still really…

Common person? No. If you are a common EE grad student, no problem. However could someone take it to a nefarious local PC repair shop with better than average skills and pay someone? Yes.

So there is a vast middle ground between naive miscreants on one end and three letter agencies.

But if you are asking whether a casual thief who steals a company laptop out of a car cares about your data? Probably no. They will wipe the drive and sell it on Craigslist. However if someone might actually target you specifically, bitlocker+tpm is not a high hurdle. But then again nor are the weak passwords your users are using, or the phishing emails they will open, or the malware apps they will install...

All security is obfuscation really. Just moves the bar higher to deter those who don’t care or don’t value your data enough. The author hinted at some techniques you can use on boards to thwart (but not prevent) a determined hacker (still not three letter agency level). Chip cos have access to all sorts of equipment to probe and access chips themselves, so even inside the chip is not safe without specific countermeasures. Three letter agencies do chemistry at government lab facilities. That’s way beyond what most people care about.

Re: Extracting Bitlocker Keys from a TPM

#26

Post by gtsteve »

tallanvor wrote: post #24
gtsteve wrote: post #21

Given Microsoft's response, it seems this isn't new. I'm in charge of my company's security so now I'm a bit concerned. I mandated the use of Bitlocker with TPM across the business but no pre-authentication measures. How accessible is this attack to the common person? Note that I am concerned about curious thieves as opposed to three letter agencies. I believe I would still be correct in saying that it's still really…

The Bitlocker + TPM without PIN model is primarily aimed at preventing the contents of a drive from being accessed from a different system - you can send your old drive to the recycler without worrying about someone hooking it up to a different computer to scan for financial information or passwords. For businesses that need to protect internal or customer data, the correct answer is requiring a PIN on boot, as this…

I suppose in retrospect it shouldn't be surprising. I just thought it would be a lot harder than this. I imagined that the communication between the TPM chip and the CPU would be encrypted somehow; I should have verified that.

Does the TPM have a mechanism to lock out if the PIN is entered incorrectly? That sounds like a good move to me.

Re: Extracting Bitlocker Keys from a TPM

#27

Post by tallanvor »

gtsteve wrote: post #26
tallanvor wrote: post #24

Earlier quoted context omitted.

The Bitlocker + TPM without PIN model is primarily aimed at preventing the contents of a drive from being accessed from a different system - you can send your old drive to the recycler without worrying about someone hooking it up to a different computer to scan for financial information or passwords. For businesses that need to protect internal or customer data, the correct answer is requiring a PIN on boot, as this…

I suppose in retrospect it shouldn't be surprising. I just thought it would be a lot harder than this. I imagined that the communication between the TPM chip and the CPU would be encrypted somehow; I should have verified that. Does the TPM have a mechanism to lock out if the PIN is entered incorrectly? That sounds like a good move to me.

Yes. By default you get 3 or 5 chances and then you have to use the recovery key. In corporate environments the recovery key is often stored in AD or another location by default so it's retrievable by IT (whether because the user entered the wrong PIN or because they quite /were fired and you still need to be able to get data off the computer.

Re: Extracting Bitlocker Keys from a TPM

#29

Post by close04 »

thisacctforreal wrote: post #22
close04 wrote: post #18

Earlier quoted context omitted.

> This post will look at extracting the clear-text key from a TPM chip by sniffing the LPC bus It is a very interesting read but the title is a bit clickbaity. Luckily it's not with bad intentions, the first few lines (above) already tell you what it is. > I'm not sure what the distinction you're making is Imagine I tell you I can extract any information I want from the human brain. You'd be intrigued, how do I inter…

Honestly it feels like splitting hairs, unless I'm misunderstanding something. What is there to gain "cracking" the TPM itself, if you can get the keys fine by sniffing? Apple's Secure Enclaves aren't vulnerable to sniffing, as the AES keys used for encryption live only in silicon, with access to use them granted to the Enclave. The keys never exist in a software-readable form, even to the coveted Enclave firmware. D…

> What is there to gain "cracking" the TPM itself

The technical achievement itself. :) It would be a world first, unlike sniffing. Hacking the TPM chip itself could open the door to even more interesting stuff. I think the analogy I gave before perfectly illustrates the difference between the 2 ideas. Getting to the same end result doesn't mean the paths are equivalent.

Would you find it equally interesting to read about getting Bitlocker keys using the legendary xkcd $5 wrench [0]?

[0] https://xkcd.com/538/

Re: Extracting Bitlocker Keys from a TPM

#30

Post by als0 »

close04 wrote: post #29
thisacctforreal wrote: post #22

Earlier quoted context omitted.

Honestly it feels like splitting hairs, unless I'm misunderstanding something. What is there to gain "cracking" the TPM itself, if you can get the keys fine by sniffing? Apple's Secure Enclaves aren't vulnerable to sniffing, as the AES keys used for encryption live only in silicon, with access to use them granted to the Enclave. The keys never exist in a software-readable form, even to the coveted Enclave firmware. D…

> What is there to gain "cracking" the TPM itself The technical achievement itself. :) It would be a world first, unlike sniffing. Hacking the TPM chip itself could open the door to even more interesting stuff. I think the analogy I gave before perfectly illustrates the difference between the 2 ideas. Getting to the same end result doesn't mean the paths are equivalent. Would you find it equally interesting to read a…

I’m not convinced it would be a world first. Certainly not for nation states :) but you should definitely check out the amazing work by Chris Tarnovsky on YouTube. The level of detail he goes into when decamping the chip... and the way he explains it all leaves me in a state of awe.
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