Provided by: tpm2-tools_5.4-1_amd64 
NAME
tpm2_ecdhzgen(1) - Recovers the shared secret value (Z) from a public point and a
specified private key.
SYNOPSIS
tpm2_ecdhzgen [OPTIONS]
DESCRIPTION
tpm2_ecdhzgen(1) - Recovers the shared secret value (Z) from a public point and a
specified private key. It will perform the multiplication of the provided inPoint (QB)
with the private key (ds) and return the coordinates of the resultant point (Z = (xZ , yZ)
≔ [hds]QB; where h is the cofactor of the curve).
OPTIONS
• -c, --key-context=FILE:
Context object pointing to ECC key. Either a file or a handle number. See section
“Context Object Format”.
• -p, --key-auth=AUTH:
The authorization value for the ECC key object.
• -u, --public=FILE:
Output ECC point Q.
• -o, --output=FILE
Specify file path to save the calculated ecdh secret or Z point.
• --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.
References
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
• sm4
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
• sm2
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.
• 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.
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
• sm2
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.
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
tpm2_createprimary -C o -c prim.ctx -Q
tpm2_create -C prim.ctx -c key.ctx -u key.pub -r key.priv -G ecc256:ecdh
tpm2_ecdhkeygen -u ecdh.pub -o ecdh.priv -c key.ctx
tpm2_ecdhzgen -u ecdh.pub -o ecdh.dat -c key.ctx
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.linuxfoundation.org/mailman/listinfo/tpm2)