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. 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:


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.


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 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:


    Specify the default (abrmd) tcti and a config string of bus_type=session:


    NOTE: abrmd and tabrmd are synonymous.