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 ALSOtpm_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)
