tpm2_changeauth - Man Page

Changes authorization values for TPM objects.


tpm2_changeauth [Options] [ARGUMENT]


tpm2_changeauth - Configures authorization values for the various hierarchies, NV indices, transient and persistent objects.

Note: For non-permanent objects (Transient objects and Persistent objects), copies of the private information (files or persistent handles) created prior to changing auth are not invalidated.


Passwords should follow the “password authorization formatting standards”, see section “Authorization Formatting”.

Objects that can move outside of TPM need to be protected (confidentiality and integrity). For instance, transient objects require that TPM protected data (key or seal material) be stored outside of the TPM. This is seen in tools like tpm2_create(1), where the -r option outputs this protected data. This blob contains the sensitive portions of the object. The sensitive portions of the object are protected by the parent object, using the parent’s symmetric encryption details to encrypt the sensitive data and HMAC it.

In-depth details can be found in sections 23 of:

Notably Figure 20, is relevant, even though it’s specifically referring to duplication blobs, the process is identical.

If the output is from tpm2_duplicate(1), the output will be slightly different, as described fully in section 23.


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:

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 specified”.


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.


A string password, specified by prefix “str:” or it’s absence (raw string without prefix) is not interpreted, and is directly used for authorization.




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.




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.


# to use stdin and be prompted

# to use a file from a path

# 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


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). Optionally, 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.


To use a session context file called session.ctx.


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


To use a session context file called session.ctx AND send the HEX authvalue 0x11223344.


PCR Authorizations

You can satisfy a PCR policy using the “pcr:” prefix and the PCR minilanguage. 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


To satisfy a PCR policy of sha256 on banks 0, 1, 2 and 3 use a specifier of:


specifying AUTH.

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:


Set owner, endorsement and lockout authorizations to newpass

tpm2_changeauth -c owner newpass
tpm2_changeauth -c endorsement newpass
tpm2_changeauth -c lockout newpass

Change owner, endorsement and lockout authorizations

tpm2_changeauth -c o -p newpass newerpass
tpm2_changeauth -c e -p newpass newerpass
tpm2_changeauth -c l -p newpass newerpass

Set owner authorization to empty password

tpm2_changeauth -c o -p oldpass

Modify authorization for a loadable transient object

tpm2_createprimary -Q -C o -c prim.ctx

tpm2_create -Q -g sha256 -G aes -u -r key.priv -C prim.ctx

tpm2_load -C prim.ctx -u -r key.priv -n -c key.ctx

tpm2_changeauth -c key.ctx -C prim.ctx -r key.priv newkeyauth

Modify authorization for a NV Index

Requires Extended Session Support.

tpm2_startauthsession -S session.ctx

tpm2_policycommandcode -S session.ctx -L policy.nvchange TPM2_CC_NV_ChangeAuth
tpm2_flushcontext session.ctx

tpm2_nvdefine   $NVIndex -C o -s 32 -a "authread|authwrite" -L policy.nvchange
tpm2_startauthsession \--policy-session -S session.ctx

tpm2_policycommandcode -S session.ctx -L policy.nvchange TPM2_CC_NV_ChangeAuth

tpm2_changeauth -p session:session.ctx -c $NVIndex newindexauth


Tools can return any of the following codes:


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tpm2-tools General Commands Manual