tpm2_policypassword man page

tpm2_policypassword(1) — Enables binding a policy to the authorization value of the authorized TPM object.

Synopsis

tpm2_policypassword [Options]

Description

tpm2_policypassword(1) - Enables a policy that requires the object's authentication passphrase be provided. This is equivalent to authenticating using the object passphrase in plaintext, only this enforces it as a policy. It provides a mechanism to allow for password authentication when an object only allows policy based authorization, ie object attribute "userwithauth" is 0.

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

We want to authenticate using the TPM objects plaintext authentication value. While we could authenticate with an ephermal password session, in this example we will authenticate with the plaintext passphrase in a policy session instead using the tpm2_policypassword(1) tool.

Create the password policy

tpm2_startauthsession -S session.dat

tpm2_policypassword -S session.dat -L policy.dat

tpm2_flushcontext session.dat

Create the object with a passphrase and the password policy

tpm2_createprimary -C o -c prim.ctx

tpm2_create -g sha256 -G aes -u key.pub -r key.priv -C prim.ctx -L policy.dat \
  -p testpswd

Authenticate with plaintext passphrase input

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

echo "plaintext" > plain.txt
tpm2_encryptdecrypt -c key.ctx -o encrypt.out plain.txt -p testpswd plain.txt

Authenticate with password and the policy

tpm2_startauthsession \--policy-session -S session.dat

tpm2_policypassword -S session.dat -L policy.dat

tpm2_encryptdecrypt -c key.ctx -o encrypt.out \
  -p session:session.dat+testpswd plain.txt

tpm2_flushcontext session.dat

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