tpm2_policycphash - Man Page

Couples a policy with command parameters of the command.

Synopsis

tpm2_policycphash [Options]

Description

tpm2_policycphash(1) - Couples a policy with command parameters of the command. This is a deferred assertion where the hash of the command parameters in a TPM command is checked against the one specified in the policy.

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

Restrict the value that can be set through tpm2_nvsetbits.

Define NV index object with authorized policy

openssl genrsa -out signing_key_private.pem 2048
openssl rsa -in signing_key_private.pem -out signing_key_public.pem -pubout
tpm2_loadexternal -G rsa -C o -u signing_key_public.pem -c signing_key.ctx \
-n signing_key.name
tpm2_startauthsession -S session.ctx -g sha256
tpm2_policyauthorize -S session.ctx -L authorized.policy -n signing_key.name
tpm2_flushcontext session.ctx
tpm2_nvdefine 1 -a "policywrite|authwrite|ownerread|nt=bits" -L authorized.policy

Create policycphash

tpm2_nvsetbits 1 -i 1 --cphash cp.hash
tpm2_startauthsession -S session.ctx -g sha256
tpm2_policycphash -S session.ctx -L policy.cphash --cphash cp.hash
tpm2_flushcontext session.ctx

Sign and verify policycphash

openssl dgst -sha256 -sign signing_key_private.pem \
-out policycphash.signature policy.cphash
tpm2_verifysignature -c signing_key.ctx -g sha256 -m policy.cphash \
-s policycphash.signature -t verification.tkt -f rsassa

Satisfy policycphash and execute nvsetbits

tpm2_startauthsession -S session.ctx --policy-session -g sha256
tpm2_policycphash -S session.ctx --cphash cp.hash
tpm2_policyauthorize -S session.ctx -i policy.cphash -n signing_key.name \
-t verification.tkt
tpm2_nvsetbits 1 -i 1 -P "session:session.ctx"
tpm2_flushcontext 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)

Info

tpm2-tools General Commands Manual