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ROCA vulnerability was discovered (October 2017) in a software library, RSALib, provided by Infineon Technologies. That library is also used in TPM modules. When this vulnerability is present, a pair of prime numbers used for generating RSA keys is chosen from a small subset of all available prime numbers. This results in a great loss of entropy. Details and exact numbers can be found here.
UPDATE 2021-10-20: provided new link for TPM firmware updates (old one was no longer working), added info about patch for openssl-1.1.0 being applied upstream.
UPDATE 2021-11-18: updated second link referring to the TPM firmware updates (it was not fixed in the UPDATE 2021-10-20).
Discovering whether TPM is vulnerable
All vulnerable keys have the same structure. This structure is visible in the public part of the key, so only the public key is required to check for ROCA. Note that when prime numbers are generated randomly there is still a chance that non-vulnerable generator will produce a key with the same structure. This chance is marginally small, compared to the whole space of available numbers, but there is a possibility of a false positive result. For the version of detection tool we will use it is 2^-154 - consider yourself very lucky if you manage to get a false positive.
Generating RSA key pairs with TPM
RSA keys can be generated with tpm2-tools. SLB 9665 used in TPM module doesn’t support 512-bit RSA, so either 1024 or 2048-bit keys must be used. Because of that, it is impossible to factorize the private part in reasonable time for testing purposes, but that time (around 3 months of CPU time according to the paper mentioned earlier) is very low when it comes to the security of keys and, moreover, data and identities protected by them. Even worse, this time scales linearly with the number of cores.
Context is used for key generation, so it must be generated first:
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Only the public key is actually required by vulnerability check. It is a good idea to generate more than one pair, probably using different key sizes - chances for false positives are extremely low, but not zero.
TPM has a limited amount of the internal RAM and runs out of memory after 3 operations with error:
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In this case either rebooting or
flushing open handles manually
helps. Only handles-transient need to be flushed:
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Extracting keys hashes
File key.pub is a binary file with a TPM-specific header. It is not supported
by the tool for checking for ROCA vulnerability, so the key needs to be
extracted and saved in one of the supported formats, e.g. hex coded number. This
can be done with the following script:
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The header is 22 bytes long, followed by the size of the key (2 bytes) and the key itself. The key is the last field in the file, so it isn’t necessary to know its size - it is needed only for keys in memory.
Testing for ROCA vulnerability
A tool for checking for ROCA TPM vulnerability can be found
here. The easiest way is to install it
with pip:
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All parsed keys can be checked using just one command:
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More use cases can be found on the main page of this tool, including tests for saved SSH hosts keys.
This operation should take no more than a couple of seconds, as it only checks if the key was generated from insecure prime numbers, without finding the exact numbers used. It does not generate private keys.
Results
This is output from test run on 2 different modules, with both 1024 and 2048-bit keys generated on each of them:
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It shows that ROCA vulnerability is present on this TPM module model. TPM firmware update will be required.
Note that ROCA is connected only with RSA, it doesn’t affect any other security functions, as long as they don’t use RSALib.
Updating TPM firmware
Tools for updating Infineon TPM firmware can be easily found, unfortunately,
most of them are either UEFI or Windows applications. A Linux port of them can
be found here. It
requires openssl-1.0 (both developer files and runtime library), but it can be
updated to 1.1.0 version using
this patch.
EDIT: Patch has already been committed to main branch.
First, check if TPMFactoryUpd was built successfully and TPM is detected
properly:
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Remember the current firmware version number, it will be needed later. Also,
note what is the value of TPM platformAuth - it must be Empty Buffer in
order to perform an update. To do this, build and flash coreboot with TPM
disabled in the config menu, or use an older version of BIOS - none of the
v4.8.0.* versions have TPM support enabled. SeaBIOS doesn’t need any
modifications, it will not initialize TPM unless coreboot does. BIOS from other
vendors might include an option to turn TPM off - keep in mind that doing so
will probably mess up things like a Secure Boot or HDD encryption.
TPM firmwares are available with some of the UEFI and Windows images, like
these.
Only
9665FW update package_1.5/Firmware/TPM20_<old_version>_to_TPM20_5.63.3144.0.BIN
file is required. Extract this file to the same directory as the TPMFactoryUpd
and run:
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This can take 3-5 minutes, depending on the firmware update size. After it completes, TPM is not useful until the next reboot:
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Reboot platform immediately. Using TPM functions in this state isn’t safe. After successful reboot and flashing original coreboot firmware the result should be:
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Updating TPM firmware - automatic version detection
Assuming that a whole Firmware directory was extracted to the directory
containing TPMFactoryUpd from the
update package, one can use a
single command to do the update. Appropriate file is chosen automatically,
depending on the old version. The command is:
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Remember to use BIOS with TPM disabled, and re-flash newer BIOS firmware afterwards.
Summary
Repeating all steps from generating TPM context to using roca-detect shows
that the vulnerability is no longer present:
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We will check every TPM module we sell and, if necessary, update the firmware before sending them to the customers. If you ordered such module earlier or you are not sure if it is vulnerable, feel free to test them for yourself.
If you think we can help in improving the security of your firmware or you are
looking for someone who can boot your product by leveraging advanced features of
used hardware platform, feel free to book a call with
us or
drop us email to contact<at>3mdeb<dot>com. If you are interested in similar
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