tpm2_policyor man page

tpm2_policyor(1) — logically OR's two policies together.

Synopsis

tpm2_policyor [Options]

Description

tpm2_policyor(1) - Generates a policy_or event with the TPM. It expects a session to be already established via tpm2_startauthsession(1). If the input session is a trial session this tool generates a policy digest that compounds two or more input policy digests such that the resulting policy digest requires at least one of the policy events being true. If the input session is real policy session tpm2_policyor(1) authenticates the object successfully if at least one of the policy events are true.

Options

References

Common Options

This collection of options are common to many programs and provide information that many users may expect.

TCTI Configuration

The TCTI or "Transmission Interface" is the communication mechanism with the TPM. TCTIs can be changed for communication with TPMs across different mediums.

To control the TCTI, the tools respect:

  1. The command line option -T or --tcti
  2. The environment variable: TPM2TOOLS_TCTI.

Note: The command line option always overrides the environment variable.

The current known TCTIs are:

The arguments to either the command line option or the environment variable are in the form:

<tcti-name>:<tcti-option-config>

Specifying an empty string for either the <tcti-name> or <tcti-option-config> results in the default being used for that portion respectively.

TCTI Defaults

When a TCTI is not specified, the default TCTI is searched for using dlopen(3) semantics. The tools will search for tabrmd, device and mssim TCTIs IN THAT ORDER and USE THE FIRST ONE FOUND. You can query what TCTI will be chosen as the default by using the -v option to print the version information. The "default-tcti" key-value pair will indicate which of the aforementioned TCTIs is the default.

Custom TCTIs

Any TCTI that implements the dynamic TCTI interface can be loaded. The tools internally use dlopen(3), and the raw tcti-name value is used for the lookup. Thus, this could be a path to the shared library, or a library name as understood by dlopen(3) semantics.

Tcti Options

This collection of options are used to configure the various known TCTI modules available:

Examples

Creates two sets of PCR data files, one of them being the existing PCR values and other being a set of PCR values that would result if the PCR were extended with a known value. Now create two separate policy digests, each with one set of the PCR values using tpm2_policypcr(1) tool in trial sessions. Now build a policy_or with the two PCR policy digests as inputs. Create a sealing object with an authentication policy compounding the 2 policies with tpm2_policyor and seal a secret. Unsealing with either of the PCR sets should be successful.

Create two unique pcr policies with corresponding unique sets of

pcrs.

Start with pcr value 0

tpm2_pcrreset 23

PCR1 policy

tpm2_startauthsession -S session.ctx

tpm2_policypcr -S session.ctx -l sha1:23 -L set1.pcr0.policy

tpm2_flushcontext session.ctx

rm session.ctx

PCR2 policy

tpm2_pcrextend 23:sha1=f1d2d2f924e986ac86fdf7b36c94bcdf32beec15

tpm2_startauthsession -S session.ctx

tpm2_policypcr -S session.ctx -l sha1:23 -L set2.pcr0.policy

tpm2_flushcontext session.ctx

rm session.ctx

Create a policyOR resulting from compounding the two unique pcr

policies in an OR fashion

tpm2_startauthsession -S session.ctx

tpm2_policyor -S session.ctx -L policyOR \
-l sha256:set1.pcr0.policy,set2.pcr0.policy

tpm2_flushcontext session.ctx

rm session.ctx

Create a sealing object with auth policyOR created above.

tpm2_createprimary -C o -c prim.ctx

tpm2_create -g sha256 -u sealkey.pub -r sealkey.priv -L policyOR -C prim.ctx \
-i- <<< "secretpass"

tpm2_load -C prim.ctx -c sealkey.ctx -u sealkey.pub -r sealkey.priv

Attempt unsealing by satisfying the policyOR by satisfying SECOND of

the two policies.

tpm2_startauthsession -S session.ctx --policy-session

tpm2_policypcr -S session.ctx -l sha1:23

tpm2_policyor -S session.ctx -L policyOR \
-l sha256:set1.pcr0.policy,set2.pcr0.policy

unsealed=`tpm2_unseal -p session:session.ctx -c sealkey.ctx`

echo $unsealed

tpm2_flushcontext session.ctx

rm session.ctx

Extend the pcr to emulate tampering of the system software and hence

the pcr value.

tpm2_pcrextend 23:sha1=f1d2d2f924e986ac86fdf7b36c94bcdf32beec15

Attempt unsealing by trying to satisy the policOR by attempting to

satisy one of the two policies.

tpm2_startauthsession -S session.ctx --policy-session

tpm2_policypcr -S session.ctx -l sha1:23

This should fail

tpm2_policyor -S session.ctx -L policyOR \
-l sha256:set1.pcr0.policy,set2.pcr0.policy

tpm2_flushcontext session.ctx

rm session.ctx

Reset pcr to get back to the first set of pcr value

tpm2_pcrreset 23

Attempt unsealing by satisfying the policyOR by satisfying FIRST of

the two policies.

tpm2_startauthsession -S session.ctx --policy-session

tpm2_policypcr -S session.ctx -l sha1:23

tpm2_policyor -S session.ctx -L policyOR \
-l sha256:set1.pcr0.policy,set2.pcr0.policy

unsealed=`tpm2_unseal -p session:session.ctx -c sealkey.ctx`

echo $unsealed

tpm2_flushcontext session.ctx

rm session.ctx

Returns

Tools can return any of the following codes:

Limitations

It expects a session to be already established via tpm2_startauthsession(1) and requires one of the following:

Without it, most resource managers will not save session state between command invocations.

Bugs

Github Issues (https://github.com/tpm2-software/tpm2-tools/issues)

Help

See the Mailing List (https://lists.01.org/mailman/listinfo/tpm2)

Referenced By

tpm2_policypcr(1).

tpm2-tools General Commands Manual