Hi David,
The manual page you get with "man tpm_quote_tools" gives an overview of
how the programs fit together. Other than that, there is no high-level
documentation. Sorry about that. Your request for better high-level
documentation has been noted.
The use case I imagined for TPM Quote Tools involves using trusted grub
to measure the OS image, and place measurements in PCRs at boot time.
When the machine is provisioned, the correct PCR values are stored on a
remote machine charged with the responsibility of determining if the
machine booted the correct image.
After a boot, TPM Quote Tools can then be used to reliably verify that
the PCRs contain the correct measurements. The quote produced by
tpm_getquote is the evidence sent to the remote entity. The remote
entity can use tpm_verifyquote and the provisioned set of PCR values to
ensure the correct OS image has been booted. This use case should be
explained somewhere, but there is currently no mention of trusted grup
in the documentation.
Ultimately, I would like to see TPM Quote Tools integrated into the
TrouSerS distribution and retire TPM Quote Tools as a separate project.
The change of the license used by TrouSerS removes the major reason for
separation. If there is any interest by the community to merge the two
projects, I will do my part to make it so.
John
TPM QUOTE TOOLS(8) TPM QUOTE TOOLS(8)
NAME
TPM Quote Tools
PROGRAMS
tpm_mkuuid, tpm_mkaik, tpm_loadkey, tpm_unloadkey, tpm_getpcrhash,
tpm_updatepcrhash, tpm_getquote, tpm_verifyquote
DESCRIPTION
TPM Quote Tools is a collection of programs that provide support for
TPM based attestation using the TPM quote operation.
A TPM contains a set of Platform Configuration Registers (PCRs). In a
well configured machine, some of these registers are set to known val‐
ues during the boot up process or at other times. For example, a PCR
might contain the hash of a boot loader in memory before it is run.
The TPM quote operation is used to authoritatively verify the contents
of a TPM's Platform Configuration Registers (PCRs). During provision‐
ing, a composite hash of a selected set of PCRs is computed. The TPM
quote operation produces a composite hash that can be compared with the
one computed while provisioning.
To use the TPM quote operation, keys must be generated. During provi‐
sioning, an Attestation Identity Key (AIK) is generated for each TPM,
and the public part of the key is made available to entities that vali‐
date quotes.
The TPM quote operation returns signed data and a signature. The data
that is signed contains the PCRs selected for the operation, the com‐
posite hash for the selected PCRs, and a nonce provided as input, and
used to prevent replay attacks. At provisioning time, the data that is
signed is stored, not just the composite hash. The signature is dis‐
carded.
An entity that wishes to evaluate a machine generates a nonce, and
sends it along with the set of PCR used to generate the composite PCR
hash at provisioning time. For this use of the TPM quote operation,
the signed data is ignored, and the signature returned is used to vali‐
date the state of the TPM's PCRs. Given the signature, the evaluating
entity replaces the nonce in the signed data generated at provisioning
time, and checks to see if the signature is valid for the data. If so,
this check ensures the selected PCRs contain values that match the ones
measured during provisioning.
A typical scenario for an enterprise using these tools follows. The
tools expect AIKs to be referenced via one enterprise-wide Universally
Unique Identifier (UUID). The program tpm_mkuuid creates one.
For each machine being checked, an AIK is created using tpm_mkaik. The
key blob produced is bound to the UUID on its machine using tpm_load‐
key. The public key associated with the AIK is sent to the entities
that verify quotes. Finally, the expected PCR composite hash is
obtained using tpm_getpcrhash. When the expected PCR values change, a
new hash can be generated with tpm_updatepcrhash.
The program to obtain a quote, and thus measure the current state of
the PCRs is tpm_getquote. The program that verifies the quote
describes the same PCR composite hash as was measured initially is
tpm_verifyquote.
SEE ALSO
tpm_mkuuid(8), tpm_mkaik(8), tpm_loadkey(8), tpm_unloadkey(8), tpm_get‐
pcrhash(8), tpm_updatepcrhash(8), tpm_getquote(8), tpm_verifyquote(8)
Oct 2010 TPM QUOTE TOOLS(8)
David Li <[email protected]> writes:
> John,
>
> Thanks for the pointer. I installed tpmquote tool. It looks very
> interesting. However the website doesn't have much info. Is there a
> doc how to use the tool in addition to man pages? Any examples?
>
> David
>
>
> On Mon, Nov 3, 2014 at 10:09 AM, John D. Ramsdell <[email protected]>
> wrote:
>
> If you have the hashes, you can verify them using TPM Quote Tools
> <http://tpmquotetools.sourceforge.net/>. It is packaged for
> Fedora, so
> if you are using it, you can install the package with "sudo yum
> install
> tpm-quote-tools".
>
> John
>
>
>
> David Li <[email protected]> writes:
>
> > Hi Luigi,
> >
> > Thanks for the link. It's very interesting.
> >
> > My case might be different from Chromium. I don't have control
> over
> > the firmware (uEFI + option ROMs + bootloader) on the board. The
> > vendor did all the hashes using CRTM as root of trust and stored
> them
> > in the TPM PCRs. So that's my starting point assuming you trust
> all
> > the hashes inside. I don't have a requirement to do any
> verification
> > post-firmware yet.
> >
> > So my problem is how to securely verify those hash values
> against the
> > "known good ones". The know good ones are those that are
> provided by
> > the board vendor before product shipping and I have to trust. I
> am
> > trying to detect any tampering of those in the field by using
> TPM.
> >
> > Since I don't control the firmware, I have no way to store the
> know
> > good hashes (e.g for boot loader) inside a verified firmware. I
> can
> > certainly store them off board in a secure location. But I also
> heard
> > you can store them inside the TPM too.
> >
> > David
>
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