tpm2_stirrandom - Man Page

Add “additional information” into TPM RNG state.


tpm2_stirrandom [Options] [ARGUMENT]


tpm2_stirrandom(1) - Inject “additional information” as bytes into TPM entropy Protected Capability pool.

“Additional information” can be extracted from file specified as argument or being read from STDIN if argument is not specified.

Up to 128 bytes can be injected at once through standard input to tpm2_stirrandom(1).

If input file is larger than 128 bytes, tpm2_stirrandom(1) will fail.

Adding data through tpm2_stirrandom(1) will trigger a reseeding of TPM DRBG Protected Capability. It is used when performing any sensitive action on a shielded location such as loading a persistent key or acting on a Protected Capability like updating TPM firmware.


This command has no option


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:


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:


Inject from stdin using echo

echo -n "myrandomdata" | tpm2_stirrandom

Inject 64 bytes from stdin using a file

dd if=/dev/urandom bs=1 count=64 > myrandom.bin

tpm2_stirrandom < ./myrandom.bin

Inject bytes from a file and reading up to 128 bytes

dd if=/dev/urandom of=./myrandom.bin bs=1 count=42

tpm2_stirrandom ./myrandom.bin


Please be aware that even if the “additional information” added by tpm2_stirrandom(1) can be entropy gathered from other DRBG sources, the TPM has no way of determining if the value has any entropy or not. As a consequence, it will just be considered as “additional input”.

The “additional input” is as defined in NIST SP800-90A (


Tools can return any of the following codes:


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tpm2-tools General Commands Manual