tpm2_ecdhzgen(1)

📦
version 5.8 · 10 versions
, in arch rolling

💖 NAME 💖

okay bestie, welcome to tpm2_ecdhzgen(1) from the General Commands Manual. This one is literally about recovering the shared secret value (Z) from a public point and a specified private key. That’s the whole vibe. 💅

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. No cap, that’s the mission. 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).

Like… it takes your public point, multiplies it by your private key, and hands you back the coordinates of the resulting point. Math girlies stay winning. ✨

✨ 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 — Input ECC point Q.
  • -k, --public-key=FILE — Input ECC public key with 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.

yes bestie, that trailing cryptographic algorithms ALGORITHM. is literally in the page. we keep the details exactly. 💀

🛠️ 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.
  • -z, --pwd-session — Use password session instead of a HMAC session for authentication. A clear text password is passed to the TPM to authorize the action. This option can be used to avoid problems when unsalted sessions are used in OpenSSL FIPS mode. If auth values are used a salted session should be used for authentication.
  • -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. information many users may expect.
important vibe check: that bullet really does say “is is” and then ends with information many users may expect. — we’re keeping it, because bestie, facts first. 😭

🔌 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. 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 ✨

okay bestie, here's the whole glow-up journey start to finish — primary key first, then a lil ECC key that's specifically built for ECDH, then we actually do the thing 🎀

First up, make yourself a primary key and stash it in a context file. The -Q is there because we're being quiet and mysterious about it, lowkey iconic:

tpm2_createprimary -C o -c prim.ctx -Q

Then we birth the actual key child 👶💖 — and notice the -G value, it's ecc256:ecdh, so the key is locked in for ECDH duty from day one, no take-backs:

tpm2_create -C prim.ctx -c key.ctx -u key.pub -r key.priv -G ecc256:ecdh

Now for comparison vibes, here's the regular tpm2_ecdhkeygen doing its thing — public part into ecdh.pub, private part into ecdh.priv:

tpm2_ecdhkeygen -u ecdh.pub -o ecdh.priv -c key.ctx

And this page's main character ✨ — tpm2_ecdhzgen, same key context, public out to ecdh.pub, and the output landing in ecdh.dat:

tpm2_ecdhzgen -u ecdh.pub -o ecdh.dat -c key.ctx

See the difference? Same shape, different output destiny. Slay 💅

🌈 Returns 🌈

ngl, tools in this family can hand you back any of these bad boys — do a vibe check on your exit code:

  • 0 — Success. we ate. 💖
  • 1 — General non-specific error. the vague ominous one 😭
  • 2 — Options handling error. you fumbled a flag bestie
  • 3 — Authentication error. wrong password, wrong energy 🔒
  • 4 — TCTI related error. the TPM talking layer is being weird
  • 5 — Non supported scheme. Applicable to tpm2_testparams.

💀 BUGS 💀

Github Issues — that's literally where the bugs live, go yell there (politely, fr fr).

🫶 HELP 🫶

See the Mailing List — yes, the old-school mailing list, it's giving retro but it works 👑

📜 License 📜

This work is licensed under the Creative Commons Attribution 4.0 International License (CC BY 4.0). share it, remix it, just give the credit bestie 🧚

and that's the whole page, no cap 💜 — brought to you by tpm2-tools, filed under tpm2_ecdhzgen(1), and yes the footer has a version and a date on it like every good manpage deserves. go generate some Z-points, you got this ✨🎀🦋

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