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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

#31

Post by Guvante »

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…

What threat model assumes it is easier to attack fTPM than the OS that is running?

Once you are online Bitlocker does nothing and you can just attack the OS and bypass all of its protections trivially...

Your threat model here assumes arbitrary code execution as a starting point of an exploit, the security game is up for the PC once that occurs.

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

#32

Post by brunoqc »

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.

> One aspect of this is that some laptop manufacturers provide a setting to erase the TPM is the laptop is opened.

Do you mean like if you remove the screws and get inside a laptop?

Could they gain access by cutting the plastic instead (maybe Matrix parasite extraction style).

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

#33

Post by etna_ramequin »

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…

> 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.

I’m always very confused by this. TPM offers encrypted sessions (setup with the Endorsement Key) for exactly this kind of attack. Why couldn’t the firmware get the keys over an encrypted session? Is it for reliability in case certificate verification goes wrong?

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

#34

Post by mananaysiempre »

layer8 wrote: post #28

If you want Bitlocker to protect against someone stealing your laptop, you should be using a password anyway (and disable non-hibernation sleep modes).

The first point was not entirely obvious before this—your laptop being stolen is essentially the weakest[1] class of threats against which full-disk encryption makes sense, and Windows makes a big deal against not requiring anything but your usual account password for that. Is the “trusted” hardware in the TPM even doing anything now? Is boot measurement also spoofable?

(Also, this is just offensive levels of dumb—why is the key material just strolling along the bus here in plain view? There isn’t even a key exchange protocol or anything.)

[1] People are also talking about secure erase here, which, okay, is weaker, but FDE + a EEPROM in a socket that you can pull out and physically destroy does that part just as effectively.

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

#35

Post by dylan604 »

yomlica8 wrote: post #17
blibble wrote: post #13

Earlier quoted context omitted.

void encryptSector(struct context *c, long sector_no, unsigned char *data, size_t data_len) { // TODO }

This is also something to keep in mind when resale of SSDs is discussed and people recommend using the secure erase function of the SSD!

It's only securely erased after I've put about six 5/8" holes with my drill in it

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

#36

Post by als0 »

> using a fTPM would solve the problem.

All TPMs support encrypted sessions to prevent these kind of MITM attacks. You use TPM2_StartAuthSession and specify encryption with each session command. But Bitlocker doesn't use one, which is epic fail. Microsoft need to fix it.

Edit: For comparison, systemd uses encrypted sessions when using LUKS disk encryption with the TPM https://github.com/systemd/systemd/commit/acbb504eaf1be51572...

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

#37

Post by ggambetta »

What software was used to turn the raw signal into zeros and ones? I've had a similar project since forever (reading digital data off 80s-era cassette tapes), I have pretty good .wav versions of the tapes, but I haven't found the right tool (or library) to turn it into zeros and ones :( Of course the fun part will begin once I can start decoding the zeros and ones...

EDIT: I know how the bits are encoded, it's Frequency Shift Keying[0]. What I don't know is what to use to decode this into a stream of bits I can process further (with custom code).

[0] https://en.wikipedia.org/wiki/Frequency-shift_keying

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

#38

Post by veave »

yomlica8 wrote: post #10
buran77 wrote: post #4

Earlier quoted context omitted.

> If the discrete TPM has to be used, then a PIN or passphrase on BitLocker is necessary. I always considered that BitLocker without a PIN is 80% convenience and 20% security.

IIRC earlier versions of bitlocker would rely upon SSD firmware implementations for drive encryption. They stopped doing that when it was revealed many of these hardware encryption systems in common drives didn't actually work.

Wasn't it tremendously naive of Microsoft to trust that SSDs did encryption correctly? So naive that it borders incompetence and/or malice?

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

#39

Post by etna_ramequin »

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…

> What would be better would be a dTPM that is integrated e.g. into a SoC, such that there are no exposed wires anywhere without decapping the SoC. Some systems such as phones work like that, but this is hard to tell even from the technical specs.

That’s Microsoft’s Proton chip, I believe.

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

#40

Post by controversial97 »

layer8 wrote: post #30
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.

Lots of people and small companies just buy a windows laptop and are unaware that the harddrive/ssd is encrypted with bitlocker.

People who avoid making a Microsoft account to log on to a windows computer, or who don't have access to the email address they used can find themselves in difficulty later when windows won't boot or it wants the bitlocker key for some reason. You can't get their files off the drive by connecting it to another machine because the bitlocker key is not available.

Yes, people should have backups and copies of their keys but they very commonly don't.

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