Provided by: tpm2-tools_5.2-1build1_amd64 
NAME
tpm2_createak(1) - Generate attestation key with given algorithm under the endorsement
hierarchy.
SYNOPSIS
tpm2_createak [OPTIONS]
DESCRIPTION
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
OPTIONS
• -P, --eh-auth=AUTH:
The authorization value for the endorsement hierarchy.
• -p, --ak-auth=AUTH
The authorization value for the attestation key object created.
• -C, --ek-context=OBJECT:
The endorsement key object.
• -c, --ak-context=FILE:
The file path to save the object context of the attestation key.
• -G, --key-algorithm=ALGORITHM:
Specifies the attestation key algorithm. Supports:
• ecc - An P256 key.
• rsa - An RSA2048 key.
• keyedhash - hmac key.
• -g, --hash-algorithm=ALGORITHM:
Specifies the digest algorithm used for signing.
• -s, --signing-algorithm=ALGORITHM:
The signing algorithm.
• -u, --public=FILE:
The file to save the public portion of the attestation key.
• -n, --ak-name=FILE:
The file to save the attestation key name, optional.
• -r, --private=FILE:
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:
• https://trustedcomputinggroup.org/wp-content/uploads/TPM-
Rev-2.0-Part-1-Architecture-01.38.pdf
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.
• -f, --format:
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.
• -q, --ak-qualified-name=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.
References
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 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
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.
Algorithm Specifiers
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.
Simple specifiers
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
• rsa
• ecc
Symmetric
• aes
• camellia
Hashing Algorithms
• sha1
• sha256
• sha384
• sha512
• sm3_256
• sha3_256
• sha3_384
• sha3_512
Keyed Hash
• hmac
• xor
Signing Schemes
• rsassa
• rsapss
• ecdsa
• ecdaa
• ecschnorr
Asymmetric Encryption Schemes
• oaep
• rsaes
• ecdh
Modes
• ctr
• ofb
• cbc
• cfb
• ecb
Misc
• null
Complex Specifiers
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: <type>:<scheme>:<symmetric-details>
Type Specifiers
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
• aes128<mode> - 128 bit AES with optional mode (ctr|ofb|cbc|cfb|ecb). If mode is not
specified, defaults to null.
• aes192<mode> - Same as aes128<mode>, except for a 192 bit key size.
• aes256<mode> - Same as aes128<mode>, except for a 256 bit key size.
• ecc - Elliptical Curve, defaults to ecc256.
• ecc192 - 192 bit ECC
• ecc224 - 224 bit ECC
• ecc256 - 256 bit ECC
• ecc384 - 384 bit ECC
• ecc521 - 521 bit ECC
• rsa - Default RSA: rsa2048
• rsa1024 - RSA with 1024 bit keysize.
• rsa2048 - RSA with 2048 bit keysize.
• rsa4096 - RSA with 4096 bit keysize.
Scheme Specifiers
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:
oaep-sha256.
• oaep
• ecdh
• rsassa
• rsapss
• ecdsa
• ecschnorr
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.
Examples
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.
COMMON OPTIONS
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.
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
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
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.
BUGS
Github Issues (https://github.com/tpm2-software/tpm2-tools/issues)
HELP
See the Mailing List (https://lists.01.org/mailman/listinfo/tpm2)