tpm2_getrandom man page

tpm2_getrandom(1) — Retrieves random bytes from the TPM.

Synopsis

tpm2_getrandom [Options] [ARGUMENT]

Description

tpm2_getrandom(1) - Returns the next SIZE octets from the random number generator. The SIZE parameter is expected as the only argument to the tool.

Note that the TPM specification recommends that TPM's fix the number of available entry to the maximum size of a hash algorithm output in bytes.

Most TPMs do this, and thus the tool verifies that input size is bounded by property TPM2_PT_MAX_DIGEST and issues an error if it is too large.

Output defaults to stdout and binary format unless otherwise specified with -o and --hex options respectively.

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

Generate a random 20 bytes and output the binary data to a file

tpm2_getrandom -o random.out 20

Generate a random 8 bytes and output the hex formatted data to

stdout

tpm2_getrandom 8

Returns

Tools can return any of the following codes:

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