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Extracting Bitlocker Keys from a TPM

pulsesecurity.co.nz

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Re: Extracting Bitlocker Keys from a TPM

#31

Post by close04 »

als0 wrote: post #30
close04 wrote: post #29

Earlier quoted context omitted.

> 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.

Maybe nation states is a different case. When I say "world first" I mean "that we know of". But otherwise it's incredibly interesting to see work like this especially when it's about something so obscure and undocumented that the researchers have to dig up every single bit of information by themselves.

Someone obviously doesn't agree with me since in the 10s it took me to read the comment above, all of mine received an equal number of downvotes. Guess I now have a fan (and their very own small army of puppet accounts) :).

Re: Extracting Bitlocker Keys from a TPM

#32

Post by dlgeek »

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, if you can get the keys fine by sniffing?

The ability to forge remote attestations by extracting the endorsement key or various attestation identity keys that never leave the TPM in plaintext.

Re: Extracting Bitlocker Keys from a TPM

#33

Post by yjftsjthsd-h »

londons_explore wrote: post #12
pacaro wrote: post #6

FWIW in the earlier days of BitLocker (when it was called cornerstone) a preboot PIN was considered then default secure setting. Working in the 16-bit boot loader places some serious restrictions on numeric text entry. If you have to consider the 100 or so keyboard layouts that windows supported at that time, so the pin was required to be entered using function keys F1 F2 etc. because they’re on all keyboard layouts…

Perhaps it's time to move towards the Android/iOS model of having the OS unencrypted (since that isn't a secret anyway), and only do encryption of all the user data and apps. That way, the OS can get to the login prompt entirely without secret data. Obviously that's a big architecture change...

At a bare minimum you still need to sign the OS in order to prevent tampering.

Re: Extracting Bitlocker Keys from a TPM

#34

Post by kop316 »

segfaultbuserr wrote: post #14

I find the title is misleading, it did not "extract" Bitlocker keys from the inside of a TPM at all, but merely sniffed the key material on the bus. I was so excited to see the title, and so disappointed after reading it... Sniffing keys on the bus and extracting keys from a TPM are very different scenarios. If you can "extract keys from a TPM", it means you must have found a way to tamper the chip using a piece of s…

I get what your saying, but if the end result means that they were able to get the encryption keys, what's the difference?

Its kind of like if a bank had a big vault door and then a glass window to the vault. The bank robber will break the window and get all the cash. Who cares that the door wasn't breached? What the vault was supposed to protect still is gone.

Re: Extracting Bitlocker Keys from a TPM

#35

Post by sekh60 »

londons_explore wrote: post #12
pacaro wrote: post #6

FWIW in the earlier days of BitLocker (when it was called cornerstone) a preboot PIN was considered then default secure setting. Working in the 16-bit boot loader places some serious restrictions on numeric text entry. If you have to consider the 100 or so keyboard layouts that windows supported at that time, so the pin was required to be entered using function keys F1 F2 etc. because they’re on all keyboard layouts…

Perhaps it's time to move towards the Android/iOS model of having the OS unencrypted (since that isn't a secret anyway), and only do encryption of all the user data and apps. That way, the OS can get to the login prompt entirely without secret data. Obviously that's a big architecture change...

How would one guarantee the integrity of the OS?

Re: Extracting Bitlocker Keys from a TPM

#36

Post by segfaultbuserr »

kop316 wrote: post #34
segfaultbuserr wrote: post #14

I find the title is misleading, it did not "extract" Bitlocker keys from the inside of a TPM at all, but merely sniffed the key material on the bus. I was so excited to see the title, and so disappointed after reading it... Sniffing keys on the bus and extracting keys from a TPM are very different scenarios. If you can "extract keys from a TPM", it means you must have found a way to tamper the chip using a piece of s…

I get what your saying, but if the end result means that they were able to get the encryption keys, what's the difference? Its kind of like if a bank had a big vault door and then a glass window to the vault. The bank robber will break the window and get all the cash. Who cares that the door wasn't breached? What the vault was supposed to protect still is gone.

> Its kind of like if a bank had a big vault door and then a glass window to the vault. The bank robber will break the window and get all the cash. Who cares that the door wasn't breached?

A TPM without a PIN is kind of like if a bank had a big vault door and then an employee leaving the key on the office desk, the bank robber will get the key and open the door. Everyone would care whether the door itself is breached, or it was something else.

The bottomline is, if it doesn't even have a PIN code, no security is offered against an attacker with physical possession of both the motherboard and the harddrive (aka the computer), by design, and not even a considered 0day.

Re: Extracting Bitlocker Keys from a TPM

#37

Post by e12e »

gtsteve wrote: post #20
e12e wrote: post #10

This is excellent. I've been wondering/troubled about the ease of use of bitlocker. Nice to get confirmation that standard bitlocker is rubbish against real attackers. Sad however, that the only additional defense appear to be "more blind trust in hardware" and no option for key derived from a passphrase. We know from the Xbox hack that keys in cheap hw isn't secure (enough).

You actually can configure Bitlocker to accept a passphrase instead but the option isn't easy to find. https://www.windowscentral.com/how-use-bitlocker-encryption-...

Now that you mention it, I was actually aware of this possibility. But it feels a little counter-intuitive to disable security hw in order to get secure encryption.

I consider it a pretty awful state, when what you probably want: no way to decrypt drive contents based only on what you get when you steal a laptop - the user has to go through extra work.

I suppose I can understand the preference for a "secure" key storage protected by a pin - over a complex pass-phrase. But I don't understand why it's easy (or even possible) to activate bitlocker with a largely unprotected key in "safe" storage.

Re: Extracting Bitlocker Keys from a TPM

#38

Post by ragona »

GordonS wrote: post #16
ragona wrote: post #3

Ahhh, I was very concerned until I got to the part about pre-boot verification. That is definitely a critical part of full disk encryption, and should really be the default. (Although I’ll admit that it’s really annoying sometimes.)

When I first setup Bitlocker on Windows 10, I was hunting for the option to enter a pre-boot password, but couldn't find it. I don't even think it have me the option of entering a PIN. For some reason, if you have a TPM installed you need to jump through hoops to add a pre-boot PIN, and more so if you want to enable a pre-boot password. I had to flip various Windows security policy settings before it would work. a TP…

Yeah, I had to jump through the same hoops. They're really odd, and they seem like low hanging fruit in terms of improving the customer experience for BitLocker.

Re: Extracting Bitlocker Keys from a TPM

#39

Post by als0 »

sekh60 wrote: post #35
londons_explore wrote: post #12

Earlier quoted context omitted.

Perhaps it's time to move towards the Android/iOS model of having the OS unencrypted (since that isn't a secret anyway), and only do encryption of all the user data and apps. That way, the OS can get to the login prompt entirely without secret data. Obviously that's a big architecture change...

How would one guarantee the integrity of the OS?

Secure boot.

Re: Extracting Bitlocker Keys from a TPM

#40

Post by thisacctforreal »

dlgeek wrote: post #32
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, if you can get the keys fine by sniffing? The ability to forge remote attestations by extracting the endorsement key or various attestation identity keys that never leave the TPM in plaintext.

Ah I see, they can successfully protect asymmetric crypto but not symmetric.
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