tpm2_policyauthorizenv - Man Page

Allows for mutable policies by referencing to a policy from an NV index.

Synopsis

tpm2_policyauthorizenv [Options] [ARGUMENT]

Description

tpm2_policyauthorizenv(1) - This command allows for policies to change by referencing the authorization policy written to an NV index. The NV index containing the authorization policy should remain readable even for trial session. The index can be specified as raw handle or an offset value to the nv handle range "TPM2_HR_NV_INDEX".

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

Create a policypassword and write the policy digest to an NV Index. Build a policyauthorizenv policy referencing the NV index in a trial session. The resultant policy digest is then used in creation of objects.

In a policy authorization session, first satisfy the policy written to the NV index. Then run the policyauthorizenv which satisfies the authorization for the object.

Define the test NV Index to store the auth policy

nv_test_index=0x01500001
tpm2_nvdefine -C o -p nvpass $nv_test_index -a "authread|authwrite" -s 34

Define the auth policy

tpm2_startauthsession -S session.ctx
tpm2_policypassword -S session.ctx -L policy.pass
tpm2_flushcontext session.ctx

Write the auth policy to the NV Index

echo "000b" | xxd -p -r | cat - policy.pass | \
tpm2_nvwrite -C $nv_test_index -P nvpass $nv_test_index -i-

Define the policyauthorizenv

tpm2_startauthsession -S session.ctx
tpm2_policyauthorizenv -S session.ctx -C $nv_test_index -P nvpass \
-L policyauthorizenv.1500001 $nv_test_index
tpm2_flushcontext session.ctx

Create and load a sealing object with auth policy =

policyauthorizenv

tpm2_createprimary -C o -c prim.ctx

echo "secretdata" | \
tpm2_create -C prim.ctx -u key.pub -r key.priv \
-a "fixedtpm|fixedparent|adminwithpolicy" -L policyauthorizenv.1500001 -i-

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

Satisfy the auth policy stored in the NV Index and thus

policyauthorizenv

tpm2_startauthsession -S session.ctx --policy-session
tpm2_policypassword -S session.ctx
tpm2_policyauthorizenv -S session.ctx -C $nv_test_index -P nvpass $nv_test_index
tpm2_unseal -c key.ctx -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