Provided by: tpm2-tools_4.1.1-1ubuntu0.20.04.1_amd64 
NAME
tpm2_policyauthorize(1) - Allows for mutable policies by tethering to a signing authority.
SYNOPSIS
tpm2_policyauthorize [OPTIONS]
DESCRIPTION
tpm2_policyauthorize(1) - This command allows for policies to change by associating the
policy to a signing authority and allowing the policy contents to change.
1. If the input session is a trial session this tool generates a policy digest that
associates a signing authority’s public key name with the policy being authorized.
2. If the input session is real policy session tpm2_policyauthorize(1) looks for a
verification ticket from the TPM to attest that the TPM has verified the signature on
the policy digest before authorizing the policy in the policy digest.
OPTIONS
• -L, --policy=FILE:
File to save the policy digest.
• -S, --session=FILE:
The policy session file generated via the -S option to tpm2_startauthsession(1).
• -i, --input=FILE:
The policy digest that has to be authorized.
• -q, --qualification=FILE_OR_HEX:
The policy qualifier data signed in conjunction with the input policy digest. This is
unique data that the signer can choose to include in the signature and can either be a
path or hex string.
• -n, --name=FILE:
File containing the name of the verifying public key. This ties the final policy digest
with a signer. This can be retrieved with tpm2_readpublic(1)
• -t, --ticket=FILE:
The ticket file to record the validation structure. This is generated with
tpm2_verifysignature(1).
References
COMMON OPTIONS
This collection of options are common to many programs and provide information that many
users may expect.
• -h, --help=[man|no-man]: Display the tools manpage. By default, it attempts to invoke
the manpager for the tool, however, on failure will output a short tool summary. This
is the same behavior if the “man” option argument is specified, however if explicit
“man” is requested, the tool will provide errors from man on stderr. If the “no-man”
option if specified, or the manpager fails, the short options will be output to stdout.
To successfully use the manpages feature requires the manpages to be installed or on
MANPATH, See man(1) for more details.
• -v, --version: Display version information for this tool, supported tctis and exit.
• -V, --verbose: Increase the information that the tool prints to the console during its
execution. When using this option the file and line number are printed.
• -Q, --quiet: Silence normal tool output to stdout.
• -Z, --enable-errata: Enable the application of errata fixups. Useful if an errata fixup
needs to be applied to commands sent to the TPM. Defining the environment
TPM2TOOLS_ENABLE_ERRATA is equivalent. information 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:
• tabrmd - The resource manager, called tabrmd
(https://github.com/tpm2-software/tpm2-abrmd). Note that tabrmd and abrmd as a tcti
name are synonymous.
• mssim - Typically used for communicating to the TPM software simulator.
• device - Used when talking directly to a TPM device file.
• none - Do not initalize a connection with the TPM. Some tools allow for off-tpm options
and thus support not using a TCTI. Tools that do not support it will error when
attempted to be used without a TCTI connection. Does not support ANY options and MUST
BE presented as the exact text of “none”.
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:
• device: For the device TCTI, the TPM character device file for use by the device TCTI
can be specified. The default is /dev/tpm0.
Example: -T device:/dev/tpm0 or export TPM2TOOLS_TCTI=“device:/dev/tpm0”
• mssim: For the mssim TCTI, the domain name or IP address and port number used by the
simulator can be specified. The default are 127.0.0.1 and 2321.
Example: -T mssim:host=localhost,port=2321 or export
TPM2TOOLS_TCTI=“mssim:host=localhost,port=2321”
• abrmd: For the abrmd TCTI, the configuration string format is a series of simple key
value pairs separated by a `,' character. Each key and value string are separated by a
`=' character.
• TCTI abrmd supports two keys:
1. `bus_name' : The name of the tabrmd service on the bus (a string).
2. `bus_type' : The type of the dbus instance (a string) limited to `session' and
`system'.
Specify the tabrmd tcti name and a config string of bus_name=com.example.FooBar:
\--tcti=tabrmd:bus_name=com.example.FooBar
Specify the default (abrmd) tcti and a config string of bus_type=session:
\--tcti:bus_type=session
NOTE: abrmd and tabrmd are synonymous. the various known TCTI modules.
EXAMPLES
Starts a trial session, builds a PCR policy. This PCR policy digest is then an input to
the tpm2_policyauthorize(1) along with policy qualifier data and a signer public. The
resultant policy digest is then used in creation of objects.
Subsequently when the PCR change and so does the PCR policy digest, the actual policy
digest from the tpm2_policyauthorize(1) used in creation of the object will not change.
At runtime the new PCR policy needs to be satisfied along with verification of the
signature on the PCR policy digest using tpm2_policyauthorize(1)
Create a signing authority
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
Create a policy to be authorized like a PCR policy
tpm2_pcrread -opcr0.sha256 sha256:0
tpm2_startauthsession -S session.ctx
tpm2_policypcr -S session.ctx -l sha256:0 -f pcr0.sha256 -L pcr.policy
tpm2_flushcontext session.ctx
Sign the policy
openssl dgst -sha256 -sign signing_key_private.pem -out pcr.signature pcr.policy
Authorize the policy in the policy digest
tpm2_startauthsession -S session.ctx
tpm2_policyauthorize -S session.ctx -L authorized.policy -i pcr.policy -n signing_key.name
tpm2_flushcontext session.ctx
Create a TPM object like a sealing object with the authorized policy based authentication
tpm2_createprimary -C o -g sha256 -G rsa -c prim.ctx
tpm2_create -g sha256 -u sealing_pubkey.pub -r sealing_prikey.pub -i- -C prim.ctx -L authorized.policy <<< "secret to seal"
Satisfy policy and unseal the secret
tpm2_verifysignature -c signing_key.ctx -g sha256 -m pcr.policy -s pcr.signature -t verification.tkt -f rsassa
tpm2_startauthsession \--policy-session -S session.ctx
tpm2_policypcr -S session.ctx -l sha256:0 -L pcr.policy
tpm2_policyauthorize -S session.ctx -L authorized.policy -i pcr.policy -n signing_key.name -t verification.tkt
tpm2_load -C prim.ctx -u sealing_pubkey.pub -r sealing_prikey.pub -c sealing_key.ctx
unsealed=$(tpm2_unseal -p"session:session.ctx" -c sealing_key.ctx)
echo $unsealed
tpm2_flushcontext session.ctx
Returns
Tools can return any of the following codes:
• 0 - Success.
• 1 - General non-specific error.
• 2 - Options handling error.
• 3 - Authentication error.
• 4 - TCTI related error.
• 5 - Non supported scheme. Applicable to tpm2_testparams.
Limitations
It expects a session to be already established via tpm2_startauthsession(1) and requires
one of the following:
• direct device access
• extended session support with tpm2-abrmd.
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)