tpm2_changeeps(1)

NAME

tpm2_changeeps(1) - Replaces the active endorsement primary seed with a new one generated off the TPM2 RNG.

SYNOPSIS

tpm2_changeeps [OPTIONS]

DESCRIPTION

tpm2_changeeps(1) - Replaces the active endorsement primary seed with a new one generated off the TPM2 RNG. The Transient and Persistent objects under the endorsement hierarchy are lost. This command requires platform auth.

OPTIONS

•   -p, --auth=AUTH

    Specifies the AUTH for the platform. hierarchy.

•   --cphash=FILE

    File path to record the hash of the command parameters. This is commonly termed as cpHash. NOTE: When this option is selected, The tool will not actually execute the command, it simply returns a cpHash, unless rphash is also required.

•   --rphash=FILE

    File path to record the hash of the response parameters. This is commonly termed as rpHash.

•   -S, --session=FILE:

    The session created using tpm2_startauthsession. This can be used to specify an auxiliary session for auditing and or encryption/decryption of the parameters.

  References

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

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 authorization.

  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). 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.

  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 authvalue 0x11223344.

    session:session.ctx+hex:11223344

  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 (pcr.md)

  Examples

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

    pcr:sha256:0,1,2,3

specifying AUTH.

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 (https://github.com/tpm2-software/tpm2-abrmd). 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:

<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:

•   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 127.0.0.1 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:

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

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

        \--tcti:bus_type=session

    NOTE: abrmd and tabrmd are synonymous. the various known TCTI modules.

EXAMPLES

  Change the endorsement primary seed where the platform auth is NULL.

    tpm2_changeeps

Returns

Tools can return any of the following codes:

•   0 - Success.

•   1 - General non-specific error.

•   2 - Options handling error.

•   3 - Authentication error.

•   4 - TCTI related error.

•   5 - Non supported scheme. Applicable to tpm2_testparams.

Limitations

It expects a session to be already established via tpm2_startauthsession(1) and requires one of the following:

•   direct device access

•   extended session support with tpm2-abrmd.

Without it, most resource managers will not save session state between command invocations.

BUGS

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

HELP

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