tpm2_createak - Man Page
Generate attestation key with given algorithm under the endorsement hierarchy.
tpm2_createak(1) - Generate an attestation key (AK) with the given algorithm under the endorsement hierarchy. The context of the attestation key is specified via -c.
The tool outputs to stdout a YAML representation of the loaded key’s name, for example:
loaded-key: name: 000bac149518baa05540a0678bd9b624f8a98d042e46c60f4d098ba394d36fc49268
The authorization value for the endorsement hierarchy.
The authorization value for the attestation key object created.
The endorsement key object.
The file path to save the object context of the attestation key.
Specifies the attestation key algorithm. Supports:
- ecc - A NIST_P256 key by default. Alternative curves can be selected using algorithm specifiers (e.g. ecc384 or ecc_nist_p384) .
- rsa - An RSA2048 key.
- keyedhash - hmac key.
Specifies the digest algorithm used for signing.
The signing algorithm.
The file to save the public portion of the attestation key.
The file to save the attestation key name, optional.
The output file which contains the sensitive portion of the object, optional. # Protection Details
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.
Format selection for the public key output file. `tss' (the default) will output a binary blob according to the TPM 2.0 Specification. `pem' will output an OpenSSL compatible PEM encoded public key. `der' will output an OpenSSL compatible DER encoded public key. `tpmt' will output a binary blob of the TPMT_PUBLIC struct referenced by TPM 2.0 specs.
Format selection for the signature output file.
The qualified name of the attestation key object. The qualified name is the qualified name of the parent object (the EK in this instance) and the name of the object itself. Thus, the qualified name of an object serves to bind it to its parents.
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:
- If the argument is a file path, then the file is loaded as a restored TPM transient object.
If the argument is a prefix match on one of:
- owner: the owner hierarchy
- platform: the platform hierarchy
- endorsement: the endorsement hierarchy
- lockout: the lockout control persistent object
- If the argument argument can be loaded as a number it will be treat as a handle, e.g. 0x81010013 and used directly._OBJECT_.
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 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
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.
You can satisfy a PCR policy using the “pcr:” prefix and the PCR minilanguage. The PCR minilanguage is as follows:
The PCR spec is documented in in the section “PCR bank specifiers”.
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)
To satisfy a PCR policy of sha256 on banks 0, 1, 2 and 3 use a specifier of:
Options that take algorithms support “nice-names”.
There are two major algorithm specification string classes, simple and complex. Only certain algorithms will be accepted by the TPM, based on usage and conditions.
These are strings with no additional specification data. When creating objects, non-specified portions of an object are assumed to defaults. You can find the list of known “Simple Specifiers” below.
Asymmetric Encryption Schemes
Objects, when specified for creation by the TPM, have numerous algorithms to populate in the public data. Things like type, scheme and asymmetric details, key size, etc. Below is the general format for specifying this data:
This portion of the complex algorithm specifier is required. The remaining scheme and symmetric details will default based on the type specified and the type of the object being created.
- aes - Default AES: aes128
<mode>- 128 bit AES with optional mode (ctr|ofb|cbc|cfb|ecb). If mode is not specified, defaults to null.
<mode>- Same as aes128
<mode>, except for a 192 bit key size.
<mode>- Same as aes128
<mode>, except for a 256 bit key size.
- sm4 - Default SM4: sm4128
- sm4128 or sm4_128
<mode>- 128 bit SM4 with optional mode (ctr|ofb|cbc|cfb|ecb). If mode is not specified, defaults to null.
- ecc - Elliptical Curve, defaults to ecc256.
- ecc192 or ecc_nist_p192 - 192 bit ECC NIST curve
- ecc224 or ecc_nist_p224 - 224 bit ECC NIST curve
- ecc256 or ecc_nist_p256 - 256 bit ECC NIST curve
- ecc384 or ecc_nist_p384 - 384 bit ECC NIST curve
- ecc521 or ecc_nist_p521 - 521 bit ECC NIST curve
- ecc_sm2 or ecc_sm2_p256 - 256 bit SM2 curve
- rsa - Default RSA: rsa2048
- rsa1024 - RSA with 1024 bit keysize.
- rsa2048 - RSA with 2048 bit keysize.
- rsa3072 - RSA with 3072 bit keysize.
- rsa4096 - RSA with 4096 bit keysize.
Next, is an optional field, it can be skipped.
Schemes are usually Signing Schemes or Asymmetric Encryption Schemes. Most signing schemes take a hash algorithm directly following the signing scheme. If the hash algorithm is missing, it defaults to sha256. Some take no arguments, and some take multiple arguments.
Hash Optional Scheme Specifiers
These scheme specifiers are followed by a dash and a valid hash algorithm, For example:
Multiple Option Scheme Specifiers
This scheme specifier is followed by a count (max size UINT16) then followed by a dash(-) and a valid hash algorithm. * ecdaa For example, ecdaa4-sha256. If no count is specified, it defaults to 4.
No Option Scheme Specifiers
This scheme specifier takes NO arguments. * rsaes
Symmetric Details Specifiers
This field is optional, and defaults based on the type of object being created and it’s attributes. Generally, any valid Symmetric specifier from the Type Specifiers list should work. If not specified, an asymmetric objects symmetric details defaults to aes128cfb.
Create an rsa2048 key with an rsaes asymmetric encryption scheme
tpm2_create -C parent.ctx -G rsa2048:rsaes -u key.pub -r key.priv
Create an ecc256 key with an ecdaa signing scheme with a count of 4 and sha384 hash
/tpm2_create -C parent.ctx -G ecc256:ecdaa4-sha384 -u key.pub -r key.priv cryptographic algorithms ALGORITHM.
Signature Format Specifiers
Format selection for the signature output file. tss (the default) will output a binary blob according to the TPM 2.0 specification and any potential compiler padding. The option plain will output the plain signature data as defined by the used cryptographic algorithm. signature FORMAT.
This collection of options are common to many programs and provide information that many users may expect.
-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.
- -v, --version: Display version information for this tool, supported tctis and exit.
- -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.
- -Q, --quiet: Silence normal tool output to stdout.
- -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. information many users may expect.
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:
- The command line option -T or --tcti
- 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:
Specifying an empty string for either the
<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:
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:
- `bus_name' : The name of the tabrmd service on the bus (a string).
- `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
Specify the default (abrmd) tcti and a config string of
NOTE: abrmd and tabrmd are synonymous. the various known TCTI modules.
Create an Attestation Key and make it persistent
tpm2_createek -c ek.handle -G rsa -u ek.pub tpm2_createak -C ek.handle -c ak.ctx -u ak.pub -n ak.name tpm2_evictcontrol -C o -c ak.ctx 0x81010002
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.
Github Issues (https://github.com/tpm2-software/tpm2-tools/issues)
See the Mailing List (https://lists.linuxfoundation.org/mailman/listinfo/tpm2)