Ubuntu Manpage: tpm2_policycphash(1) - Couples a policy with command parameters of the command.

NAME

       tpm2_policycphash(1) - 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

       • -L, --policy=FILE:

         File to save the compounded policy digest.

       • -S, --session=FILE:

         The policy session file generated via the -S option to tpm2_startauthsession(1).

       • --cphash-input=FILE:

         The file containing the command parameter hash of the command.

       • --cphash=FILE:

         DEPRECATED, use –cphash-input instead.

   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.

• -R, --autoflush: Enable autoflush for transient objects created by the command. If a
parent object is loaded from a context file also the transient parent object will be
flushed. Autoflush can also be activated if the environment variable
TPM2TOOLS_AUTOFLUSH is is set to yes or true. 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

       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:

       • 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.linuxfoundation.org/mailman/listinfo/tpm2)