man `1 tpm2_startauthsession`

tpm2_startauthsession(1) General Commands Manual tpm2_startauthsession(1)

NAME
tpm2_startauthsession(1) - Start a session with the TPM.

SYNOPSIS
tpm2_startauthsession [OPTIONS]

DESCRIPTION
tpm2_startauthsession(1) - Starts a session with the TPM. The default
is to start a trial session unless the -a option is specified. Saves
the policy session data to a file. This file can then be used in sub-
sequent tools that can use a policy file for authorization or policy
events.

This will not work with resource managers (RMs) outside of tpm2-abrmd
(https://%20github.com/tpm2-software/tpm2-abrmd), as most RMs will
flush session handles when a client disconnects from the IPC channel.
However, when using a RM without the session gapping feature, one can
use the command TCTI to keep the connection open.

The first step is to create a socket listener that uses tpm2_send:

mknod "$HOME/backpipe" p
while [ 1 ]; do tpm2_send 0<"$HOME/backpipe" | nc -lU "$HOME/sock" 1>"$HOME/backpipe"; done;

The next step is to use the command TCTI and netcat (nc) to send data
to the socket.

tpm2_startauthsession --tcti="cmd:nc -q 0 -U $HOME/sock" <options>

When finishing ensure to kill the listener. For commands executed with
the command tcti against the listener, one will need to manage tran-
sient handles. The simplest way is to add a flush after each command:
tpm2_flushcontext --tcti="cmd:nc -q 0 -U $HOME/sock" -t

Note: This example uses UNIX sockets, since the socket is controlled
with Linux access controls. Using a port is not recommended as it's
either open to any user on the system (localhost) or bound to a network
card and exposed to the network.

This will work with direct TPM access, but note that internally this
calls a ContextSave and a ContextLoad on the session handle, thus the
session cannot be saved/loaded again.

OPTIONS
o --policy-session:

Start a policy session of type TPM_SE_POLICY. Default without this
option is TPM_SE_TRIAL.

NOTE: A trial session is used when building a policy and a policy
session is used when authenticating with a policy.

o --audit-session:

Start an HMAC session to be used as an audit session. Default with-
out this option is TPM2_SE_TRIAL.

o --hmac-session:

Start an HMAC session of type TPM_SE_HMAC. Default without this op-
tion is TPM2_SE_TRIAL.

o -g, --hash-algorithm=ALGORITHM:

The hash algorithm used in computation of the policy digest.

o -c, --key-context=OBJECT:

Set the tpmkey and bind objects to be the same. Session parameter
encryption is turned on. Session parameter decryption is turned on.
Parameter encryption/decryption symmetric-key set to AES-CFB.

o -S, --session=FILE:

The name of the policy session file, required.

o --bind-context=FILE:

Set the bind object. Session parameter encryption is off. Use
tpm2_sessionconfig to turn on. Session parameter decryption is off.
Use tpm2_sessionconfig to turn on. Parameter encryption/decryption
symmetric-key set to AES-CFB.

o --bind-auth=AUTH:

Set the authorization value for the bind object.

o --tpmkey-context=FILE:

Set the tpmkey object. Session parameter encryption is off. Use
tpm2_sessionconfig to turn on. Session parameter decryption is off.
Use tpm2_sessionconfig to turn on. Parameter encryption/decryption
symmetric-key set to AES-CFB.

References
Context Object Format
The type of a context object, whether it is a handle or file name, is
determined according to the following logic in-order:

o If the argument is a file path, then the file is loaded as a restored
TPM transient object.

o If the argument is a prefix match on one of:

o owner: the owner hierarchy

o platform: the platform hierarchy

o endorsement: the endorsement hierarchy

o lockout: the lockout control persistent object

o If the argument argument can be loaded as a number it will be treat
as a handle, e.g. 0x81010013 and used directly._OBJECT_.

Authorization Formatting
Authorization for use of an object in TPM2.0 can come in 3 different
forms: 1. Password 2. HMAC 3. Sessions

NOTE: "Authorizations default to the EMPTY PASSWORD when not speci-
fied".

Passwords
Passwords are interpreted in the following forms below using prefix
identifiers.

Note: By default passwords are assumed to be in the string form when
they do not have a prefix.

String
A string password, specified by prefix "str:" or it's absence (raw
string without prefix) is not interpreted, and is directly used for au-
thorization.

Examples
foobar
str:foobar

Hex-string
A hex-string password, specified by prefix "hex:" is converted from a
hexidecimal form into a byte array form, thus allowing passwords with
non-printable and/or terminal un-friendly characters.

Example
hex:0x1122334455667788

File
A file based password, specified be prefix "file:" should be the path
of a file containing the password to be read by the tool or a "-" to
use stdin. Storing passwords in files prevents information leakage,
passwords passed as options can be read from the process list or common
shell history features.

Examples
# to use stdin and be prompted
file:-

# to use a file from a path
file:path/to/password/file

# to echo a password via stdin:
echo foobar | tpm2_tool -p file:-

# to use a bash here-string via stdin:

tpm2_tool -p file:- <<< foobar

Sessions
When using a policy session to authorize the use of an object, prefix
the option argument with the session keyword. Then indicate a path to
a session file that was created with tpm2_startauthsession(1). Option-
ally, if the session requires an auth value to be sent with the session
handle (eg policy password), then append a + and a string as described
in the Passwords section.

Examples
To use a session context file called session.ctx.

session:session.ctx

To use a session context file called session.ctx AND send the authvalue
mypassword.

session:session.ctx+mypassword

To use a session context file called session.ctx AND send the HEX auth-
value 0x11223344.

session:session.ctx+hex:11223344

PCR Authorizations
You can satisfy a PCR policy using the "pcr:" prefix and the PCR mini-
language. The PCR minilanguage is as follows:
<pcr-spec>=<raw-pcr-file>

The PCR spec is documented in in the section "PCR bank specifiers".

The raw-pcr-file is an optional argument that contains the output of
the raw PCR contents as returned by tpm2_pcrread(1).

PCR bank specifiers (pcr.md)

Examples
To satisfy a PCR policy of sha256 on banks 0, 1, 2 and 3 use a specifi-
er of:

pcr:sha256:0,1,2,3

specifying AUTH.

COMMON OPTIONS
This collection of options are common to many programs and provide in-
formation that many users may expect.

o -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 re-
quested, the tool will provide errors from man on stderr. If the
"no-man" option if specified, or the manpager fails, the short op-
tions 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.

o -v, --version: Display version information for this tool, supported
tctis and exit.

o -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.

o -Q, --quiet: Silence normal tool output to stdout.

o -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. in-
formation 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 vari-
able.

The current known TCTIs are:

o tabrmd - The resource manager, called tabrmd
(https://github.com/tpm2-software/tpm2-abrmd). Note that tabrmd and
abrmd as a tcti name are synonymous.

o mssim - Typically used for communicating to the TPM software simula-
tor.

o device - Used when talking directly to a TPM device file.

o 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-op-
tion-config> results in the default being used for that portion respec-
tively.

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 indi-
cate 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 li-
brary name as understood by dlopen(3) semantics.

TCTI OPTIONS
This collection of options are used to configure the various known TCTI
modules available:

o 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="de-
vice:/dev/tpm0"

o 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_TC-
TI="mssim:host=localhost,port=2321"

o abrmd: For the abrmd TCTI, the configuration string format is a se-
ries of simple key value pairs separated by a `,' character. Each
key and value string are separated by a `=' character.

o 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.ex-
ample.FooBar:

\--tcti=tabrmd:bus_name=com.example.FooBar

Specify the default (abrmd) tcti and a config string of bus_type=ses-
sion:

\--tcti:bus_type=session

NOTE: abrmd and tabrmd are synonymous. the various known TCTI mod-
ules. # EXAMPLES

Start a trial session and save the session data to a file
tpm2_startauthsession -S mysession.ctx

Start a policy session and save the session data to a file
tpm2_startauthsession --policy-session -S mysession.ctx

Start an encrypted and bound policy session and save the session data to a
file
tpm2_createprimary -c primary.ctx
tpm2_startauthsession --policy-session -c primary.ctx -S mysession.ctx

Returns
Tools can return any of the following codes:

o 0 - Success.

o 1 - General non-specific error.

o 2 - Options handling error.

o 3 - Authentication error.

o 4 - TCTI related error.

o 5 - Non supported scheme. Applicable to tpm2_testparams.

BUGS
Github Issues (https://github.com/tpm2-software/tpm2-tools/issues)

HELP
See the Mailing List (https://lists.01.org/mailman/listinfo/tpm2)

tpm2-tools tpm2_startauthsession(1)

man 1 tpm2_startauthsession

man `1 tpm2_startauthsession`