tpm2_makecredential(1) General Commands Manual tpm2_makecredential(1)

tpm2_makecredential(1) - Generate the encrypted-user-chosen-data and the wrapped-secret-data-encryption-key for the privacy-sensitive credentialing process of a TPM object.

tpm2_makecredential [OPTIONS]

tpm2_makecredential(1) - The TPM supports a privacy preserving protocol for distributing credentials for keys on a TPM. The process guarantees that the credentialed-TPM-object(AIK) is loaded on the same TPM as a well-known public-key-object(EK) without knowledge of the specific public properties of the credentialed-TPM-object(AIK). The privacy is guaranteed due to the fact that only the name of the credentialed-TPM-object(AIK) is shared and not the credentialed-TPM-object’s public key itself.

Make-credential is the first step in this process where in after receiving the public-key-object(EK) public key of the TPM and the name of the credentialed-TPM-object(AIK), an encrypted-user-chosen-data is generated and the secret-data-encryption-key is generated and wrapped using cryptographic processes specific to credential activation that guarantees that the credentialed-TPM-object(AIK) is loaded on the TPM with the well-known public-key-object(EK).

tpm2_makecredential can be used to generate the encrypted-user-chosen-data and the wrapped secret-data-encryption-key without a TPM by using the none TCTI option.

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-e, --encryption-key=FILE:

DEPRECATED, use -u or –public instead.

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-u, --public=FILE:

A TPM public key which was used to wrap the seed. NOTE: This option is same as -e and is added to make it similar with other tools specifying the public key. The old option is retained for backwards compatibility.

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-G, --key-algorithm=ALGORITHM:

The key algorithm associated with TPM public key. Specify either RSA/ ECC. When this option is used, input public key is expected to be in PEM format and the default TCG EK template is used for the key properties.

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-s, --secret=FILE or STDIN:

The secret which will be protected by the key derived from the random seed. It can be specified as a file or passed from stdin.

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-n, --name=FILE:

The name of the key for which certificate is to be created.

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-o, --credential-blob=FILE:

The output file path, recording the encrypted-user-chosen-data and the wrapped secret-data-encryption-key.

This collection of options are common to many programs and provide information that many users may expect.

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-h, --help=[man|no-man]: Display the tools manpage. By default, it attempts to invoke the manpager for the tool, however, on failure will output a short tool summary. This is the same behavior if the “man” option argument is specified, however if explicit “man” is requested, the tool will provide errors from man on stderr. If the “no-man” option if specified, or the manpager fails, the short options will be output to stdout.

To successfully use the manpages feature requires the manpages to be installed or on MANPATH, See man(1) for more details.

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-v, --version: Display version information for this tool, supported tctis and exit.
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-V, --verbose: Increase the information that the tool prints to the console during its execution. When using this option the file and line number are printed.
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-Q, --quiet: Silence normal tool output to stdout.
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-Z, --enable-errata: Enable the application of errata fixups. Useful if an errata fixup needs to be applied to commands sent to the TPM. Defining the environment TPM2TOOLS_ENABLE_ERRATA is equivalent.
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-R, --autoflush: Enable autoflush for transient objects created by the command. If a parent object is loaded from a context file also the transient parent object will be flushed. Autoflush can also be activated if the environment variable TPM2TOOLS_AUTOFLUSH is is set to yes or true.

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:

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tabrmd - The resource manager, called tabrmd. Note that tabrmd and abrmd as a tcti name are synonymous.
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mssim - Typically used for communicating to the TPM software simulator.
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device - Used when talking directly to a TPM device file.
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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.

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.

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:

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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”

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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.
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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.

tpm2 createek -Q -c 0x81010009 -G rsa -u ek.pub
tpm2 createak -C 0x81010009 -c ak.ctx -G rsa -g sha256 -s rsassa -u ak.pub \
-n ak.name -p akpass> ak.out
file_size=`ls -l ak.name | awk {'print $5'}`
loaded_key_name=`cat ak.name | xxd -p -c $file_size`
tpm2 readpublic -c 0x81010009 -o ek.pem -f pem -Q
echo "12345678" | tpm2 makecredential -Q -u ek.pem -s - -n $loaded_key_name \
-o mkcred.out -G rsa

Tools can return any of the following codes:

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0 - Success.
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1 - General non-specific error.
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2 - Options handling error.
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3 - Authentication error.
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4 - TCTI related error.
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5 - Non supported scheme. Applicable to tpm2_testparams.

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