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Bypassing Bitlocker using a cheap logic analyzer on a Lenovo laptop

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Re: Bypassing Bitlocker using a cheap logic analyzer on a Lenovo laptop

#21

Post by jeroenhd »

jrm4 wrote: post #7

Bitlocker is the Windows one, that's essentially known to be compromised, right? Not saying that it's useless, might be fine for certain work environments, but I wouldn't rely on it for anything truly personal.

I'm not aware of any proven compromise of Bitlocker. There are some bugs (Bitlocker disabling itself during certain updates and not re-enabling it after a BSOD during the update process) but I haven't heard of any way for an attacker who doesn't have full code execution already to bypass encryption. If you set a PIN you should be safe, otherwise the attacker can try to use various exploits or other methods to access the drives.

For fTPM based encryption, the entire system should be safer because the keys don't traverse an accessible bus like this.

The vulnerability also applies to other encryption systems using the TPM, like LUKS disk encryption.

Re: Bypassing Bitlocker using a cheap logic analyzer on a Lenovo laptop

#22

Post by logical_person »

ongy wrote: post #20
FirmwareBurner wrote: post #5

>The use of a discrete (physical) TPM actually decreases the security of the system, using a fTPM would solve the problem. Errr... no. Using no TPM of any kind decreases your security. The discrete TPM's threat model was never designed to cover you from attackers using oscilloscope to probe your laptop's SPI bus during the boot process for unencrypted data. Unencrypted communications over any channel, SW or HW are ba…

For large symmetric operations like disk encryption, the MVK is still in memory. TPMs are slow and have rather restricted memory. They are fine for PCRs and some asymmetric operations. But here they only unseal a key that is then used in software for speed. It's worse than something protected by a high entropy password. Which is still better than 90% of users would be otherwise

that's still less secure, though. without a TPM you have no guarantee of the underlying state of firmware on the device. this enables a persistent backdoor.

TPM with no PIN is practically bitlocker with no password. A high entropy PIN happens to solve this entire attack.

Re: Bypassing Bitlocker using a cheap logic analyzer on a Lenovo laptop

#23

Post by controversial97 »

Another write up from 2021

https://arstechnica.com/gadgets/2021/08/how-to-go-from-stole...

One aspect of this is that some laptop manufacturers provide a setting to erase the TPM if the laptop is opened. You opened that laptop to see if you can add more RAM? Better hope you can access the bitlocker key or have a good backup.

Re: Bypassing Bitlocker using a cheap logic analyzer on a Lenovo laptop

#24

Post by gquere »

FirmwareBurner wrote: post #5

>The use of a discrete (physical) TPM actually decreases the security of the system, using a fTPM would solve the problem. Errr... no. Using no TPM of any kind decreases your security. The discrete TPM's threat model was never designed to cover you from attackers using oscilloscope to probe your laptop's SPI bus during the boot process for unencrypted data. Unencrypted communications over any channel, SW or HW are ba…

Author here.

> Errr... no. Using no TPM of any kind decreases your security.

You're right, I wrote too fast, sorry about that. What I meant to say is that it discrete TPM with no PIN is an inferior solution compared to PIN/passphrase or fTPM. Also I should have added that it gives the illusion of security which I hinted at in the foreword. I'm leaving it as is for now, the discussions here are interesting.

Re: Bypassing Bitlocker using a cheap logic analyzer on a Lenovo laptop

#25

Post by ongy »

logical_person wrote: post #22
ongy wrote: post #20

Earlier quoted context omitted.

For large symmetric operations like disk encryption, the MVK is still in memory. TPMs are slow and have rather restricted memory. They are fine for PCRs and some asymmetric operations. But here they only unseal a key that is then used in software for speed. It's worse than something protected by a high entropy password. Which is still better than 90% of users would be otherwise

that's still less secure, though. without a TPM you have no guarantee of the underlying state of firmware on the device. this enables a persistent backdoor. TPM with no PIN is practically bitlocker with no password. A high entropy PIN happens to solve this entire attack.

For the claim of GGP (stealing out of memory) it's worse, as that's still possible, and there's a bus the key travels over.

The PCRs attest system state to the OS, yes. Though the verified boot (PSB/Secure Guard + Secure Boot) chain is supposed to provide the same security there. Provided we assume security features aren't broken by design...

Re: Bypassing Bitlocker using a cheap logic analyzer on a Lenovo laptop

#26

Post by FirmwareBurner »

c4mpute wrote: post #15
FirmwareBurner wrote: post #5

>The use of a discrete (physical) TPM actually decreases the security of the system, using a fTPM would solve the problem. Errr... no. Using no TPM of any kind decreases your security. The discrete TPM's threat model was never designed to cover you from attackers using oscilloscope to probe your laptop's SPI bus during the boot process for unencrypted data. Unencrypted communications over any channel, SW or HW are ba…

This is highly misleading. fTPM is more secure against _this_ kind of attack, with physical access to the bus wires. However, since fTPM is a Firmware-TPM, it is vulnerable to all kinds of attacks on the system's firmware, even remotely, even via the network, even maybe if the computer is switched off. Remember all those (even unauthenticated, remote) XML-parser exploits in the Intel ME? fTPM is just one more ME modu…

>fTPM is more secure against _this_ kind of attack, with physical access to the bus wires. However, since fTPM is a Firmware-TPM, it is vulnerable to all kinds of attacks on the system's firmware, even remotely

Yes, fTPM is more vulnerable in theory to remote attacks, but fTPM could always be patched, while it's more difficult to de-solder the TPM chip off your motherboard and replace with a non-vulnerable one and there are vulnerable dTPM chips out there.

Both solutions have their own pros and cons you have to weigh in the context of cost, convenience and threat model.

>What would be better would be a dTPM that is integrated e.g. into a SoC

Isn't that what fTPM is? The TPM spec firmware runs on the security microcontroller (Intel PTT and AMD PSP) built in the same SoC as the CPU.

What would be better is having the TPM be removable from the machine, like the YubiKey. Currently, dTPM and fTPM are basically like having your YubiKey always plugged in and glued to your machine. Convenient for authenticating you, but not secure from guys stealing your machine and probing it in a lab.

Re: Bypassing Bitlocker using a cheap logic analyzer on a Lenovo laptop

#27

Post by hedora »

jeroenhd wrote: post #21
jrm4 wrote: post #7

Bitlocker is the Windows one, that's essentially known to be compromised, right? Not saying that it's useless, might be fine for certain work environments, but I wouldn't rely on it for anything truly personal.

I'm not aware of any proven compromise of Bitlocker. There are some bugs (Bitlocker disabling itself during certain updates and not re-enabling it after a BSOD during the update process) but I haven't heard of any way for an attacker who doesn't have full code execution already to bypass encryption. If you set a PIN you should be safe, otherwise the attacker can try to use various exploits or other methods to access…

It sends escrow keys to your employer in enterprise environments.

I’d be a bit surprised if the azure compromise a few weeks ago didn’t also give the attackers access to the escrow keys for customer vms, etc.

Re: Bypassing Bitlocker using a cheap logic analyzer on a Lenovo laptop

#29

Post by gbil »

gquere wrote: post #24
FirmwareBurner wrote: post #5

>The use of a discrete (physical) TPM actually decreases the security of the system, using a fTPM would solve the problem. Errr... no. Using no TPM of any kind decreases your security. The discrete TPM's threat model was never designed to cover you from attackers using oscilloscope to probe your laptop's SPI bus during the boot process for unencrypted data. Unencrypted communications over any channel, SW or HW are ba…

Author here. > Errr... no. Using no TPM of any kind decreases your security. You're right, I wrote too fast, sorry about that. What I meant to say is that it discrete TPM with no PIN is an inferior solution compared to PIN/passphrase or fTPM. Also I should have added that it gives the illusion of security which I hinted at in the foreword. I'm leaving it as is for now, the discussions here are interesting.

Some months ago my company (in the 200k+ employees big) decided to remove pin requirement to “enhance UX while staying secure”. Many objections from quite a few people, mine included pointing to PoC key extractions from TPM etc. and… nothing . Seems that a multi billion company with no-ask money for cybersecurity misses the basics

Re: Bypassing Bitlocker using a cheap logic analyzer on a Lenovo laptop

#30

Post by layer8 »

controversial97 wrote: post #23

Another write up from 2021 https://arstechnica.com/gadgets/2021/08/how-to-go-from-stole... One aspect of this is that some laptop manufacturers provide a setting to erase the TPM if the laptop is opened. You opened that laptop to see if you can add more RAM? Better hope you can access the bitlocker key or have a good backup.

It’s good practice to have a copy of the recovery key somewhere.
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