pascal-gujer/SPITkey

Decrypt the bitlocker FVEK for a bitlocker encrypted drive.

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Requirements

These scripts require: python3: https://www.python.org/downloads/
pycryptodome: "pip install pycryptodome"

optionally: wireshark: https://www.wireshark.org/download.html

SPITkey

Usage: spitkey.py -l $LOG [-p $PIN -t $TPMblob] [-k $VMK] [-r $RECOVERY] [-b $BEK]

Decrypt the bitlocker FVEK for a bitlocker encrypted drive. All methods require the output of the command dislocker -vvvv /dev/$bitlockerpartition as this contains important metadata and the encrypted keys.

In addition:

• KEY only requires
  • The BEK file
• TPM only requires
  • The VMK sniffed from the TPM
• TPMandPIN requires
  • The PIN
  • The blob of data returned from the TPM by the unseal command
• TPMandKEY requires
  • The BEK file
  • The VMK sniffed from the TPM
• TPMandPINandKEY requires
  • The BEK file
  • The PIN
  • The blob of data returned from the TPM by the unseal command
• Recovery requires
  • The recovery key

Note

Please note the sniffed data from the TPM is handled differently depending on the mode
If bitlocker is in TPM or TPMandKEY the data you sniff is a key and use -k $key
If bitlocker is in TPMandPIN or TPMandPINandKEY the data is an encrypted blob and use -t $blob

sigrok2pcap

Usage: sigrok2pcap.py input_file -p (write pcap) -k (write keys)

Convert exported csv data from libsigrokdecoder_spi-tpm.

• -p will output a text file suitable for use with wiresharks text2pcap.exe If this is present it will be called to convert the file automatically.
• -k will extract the VMK or Blob and save it.

logic2pcap

Usage: logic2pcap.py input.csv -p (write pcap) -k (write keys)

Convert exported csv data from locic2 using Withsecure's "TPM SPI" analyser

• -p will output a text file suitable for use with Wireshark's text2pcap.exe If this is present it will be called to convert the file automatically
• -k will extract the VMK or Blob and save it.

Important

When exporting data from logic2 to a csv ensure the "TPM SPI" analyser's "operation selector" is set to export both read and write data

swtpm2pcap

Usage: swtpm2pcap.py input_file -p (write pcap) -k (write keys)

Convert the verbose log of an emulated tpm in QEMU using the swtpm package

• -p will output a text file suitable for use with wiresharks text2pcap.exe If this is present it will be called to convert the file automatically
• -k will extract the VMK or Blob and save it.

This was writen when testing and is only left in incase it of use to someone. To output tpm traffic in the logfile swtpm needs to be called with the option --log level=20

blob2john

Usage: blob2john.py -l $dislocker-log -t $TPMblob

Extract data from a sniffed TPM blob and a dislocker log and output a hash file in a format suitable for trying to crack the PIN with Hashcat, John the ripper or bitcracker Requires:

• The blob of data from the TPM unseal command

• The output of dislocker -vvvv /dev/$bitlockerpartition

Sniffing the SPI bus

Sniffing the data from the TPM will require a suitably fast logic analyser that is supported by pulseview or Logic2.

SPI TPM's have a minimum bus speed of 10 - 24 MHz however the Trusted Computing Group encourage support for frequencies between 33MHz and 66MHz. As a rule of thumb you ideally need a sample rate at least 4 times faster than the bus speed for example a 43MHz Infineon 9670 would need an analyser than can sample 4 channels (MISO MOSI SCLK CS#) at a minimum of 172 MHz and if possible faster.

Software setup

The required software is dictated by the logic analyser hardware being used Either Pulseview and libsigrokdecoder_spi-tpm or Logic2 and WithSecures "TPM SPI" analyser for Saleae devices

Pulseview

Install Pulseview https://sigrok.org/wiki/Downloads

Install the libsigrokdecoder_spi-tpm stacked decoder. https://github.com/ghecko/libsigrokdecoder_spi-tpm

To install this click on code then download zip to download the plugin. Unzip the libsigrokdecoder_spi-tpm-main.zip and it should unzip to a folder called libsigrokdecoder_spi-tpm-main rename this to "spi_tpm" and then copy this folder and its contents to "C:\Program Files\sigrok\PulseView\share\libsigrokdecode\decoders" It is important you name the folder spi_tpm as pulseview expects the folder name and the plugin id to match eg. "id = 'spi_tpm'"

Logic2

Install Logic2 https://www.saleae.com/downloads/

Install WithSecures "TPM SPI" analyzer from their bitlocker spi toolkit https://github.com/WithSecureLabs/bitlocker-spi-toolkit

This repo also contains some slightly edited versions of these plugins which will find both keys and the encrypted blob and display the key/blob in a full width bubble on the main trace display as well as in the terminal. They are in the "logic2-plugins" folder

Both

On a machine running Linux or a linux VM Install dislocker https://github.com/Aorimn/dislocker

The output of dislocker -vvvv /dev/encryptedpartition is required to decrypt the TPMandPIN blob and recover the FVEK. Connect the bitlocker encrypted drive to a machine running linux or a linux VM and find the bitlocker partition with sudo fdisk -l

The partition will show as "Microsoft basic data" on a device that isn't usb in this example /dev/nvme0n1p3
(note lowercase v for verbosity and uppercase V for volume)
sudo dislocker -vvvv -V /dev/nvme0n1p3 > dislocker.log
or
sudo dislocker -vvvv -l dislocker.log -V /dev/nvme0n1p3
This will create a file "dislocker.log" with the information you need.

If you wish to convert and view the recorded TPM data as pcaps. Install wireshark https://www.wireshark.org/

Exporting trace data - Pulseview

Once you have setup pulseview and connected the logic analyser to the TPM you can record the spi bus then add first the SPI protocol decoder then once that is configured select stack decoder and add the "SPI TPM" stackable decoder and select the tpm type 1.2 or 2.0.

At this point it should have (slowly) decoded the TPM traffic and you should see some decoded data below the traces. If the target PC had bitlocker configured for TPM only there should be a trace labled "SPI TPM: BitLocker Volume Master Key" if this is the case that key can either be used directly with dislocker to unlock the drive or you can use SPITkey with the key and a dislocker logfile to recover the FVEK.

If the PC is using TPMandPIN or you wish to export a PIN only trace to a pcap the data needed for conversion to pcap is the trace labeled "SPI TPM: TPM transactions" to save this right click on the trace and select "Export all annotations for this row" and save the annotations as a text file. This Text file can then be converted to a pcap and/or searched for keys using sigrok2pcap.py input_file -p -k the pcap file can then be opened in wireshark or key data read directly from the found data files.

If the PC was using TPMandPIN and you know the PIN you can now use the sniffed data blob, the PIN and the dislocker log to recover the FVEK using SPITkey.py.

If the PC was using TPMandPIN and you have built an implant and somehow managed to get the blob but don't know the PIN, well done! You can use blob2john and the dislocker log to extract the hash needed to attepmt to bruteforce the PIN with John the ripper, hashcat or bitcracker.

Exporting trace data - Logic2

Launch Logic2 and select the SPI analyser and setup your channels.
In the the Extension tab click on the 3 dots and select "load existing extension" and add both of the WithSecure plugins "Bitlocker Key Extractor" and "TPM SPI Transaction"
On the analysers tab deselect "Stream to Terminal" and "Show in data table" for the SPI analyser as we don't need that data but the extensions require that.

For the TPM SPI extension select edit and change "operation selector" to both so when you export the data it will have both read and write data.

Now capture the spi data, if it was in PIN only the "Bitlocker Key Extractor" should have logged the key to the terminal. If not or you want to export the data to a pcap on the data table select export table and save the data as a CSV which you can convert to a pcap or extract the keys from using logic2pcap

Extracting the key from a trace

With the trace exported to a csv from logic2 or sigrock run the appropriate x2pcap.py script using the -k argument will export the VMK or blob to a file and the -p flag will export the data to a pcap if you wish to view it in wireshark.

Decrypting the blob and or FVEK

With the key or blob extracted from the csv run SPITKey.py with the appropriate inputs for the protector in use (eg TPMandPIN needs the blob, the pin and the metadata) This will then decrypt the FVEK and save it out to a file so you can use it with dislocker. If the drive is using TPM only you can skip this step and just use the VMK extracted from the CSV with dislocker.