tpm2_createak(1)

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version 5.8 · 10 versions
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🎀 tpm2_createak(1) 🎀

okay so this is the General Commands Manual page for tpm2_createak(1), and it’s genuinely iconic — we’re generating attestation keys under the endorsement hierarchy. Let’s get into it, bestie 💖

✨ NAME ✨

tpm2_createak(1) — generate attestation key with given algorithm under the endorsement hierarchy. Periodt.

🦋 SYNOPSIS 🦋

tpm2_createak [OPTIONS]

🌸 DESCRIPTION 🌸

tpm2_createak(1) generates 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 — 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.
  • -a, --attributes=ATTRIBUTES — the object attributes, optional. The default for created objects is: restricted|userwithauth|sign|fixedtpm|fixedparent|sensitivedataorigin This default setting differs from the settings in the specification TPM 2.0 Keys for Device Identity and Attestation. adminwithpolicy is not set and can be added to the default: restricted|userwithauth|...|adminwithpolicy
  • -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:

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.

Back to the option list, bestie 🫶

  • -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”.

For authentication with auth values, the tool commands implicitly generate an HMAC session. Thus passwords are not transmitted unencrypted. This does not apply to passwords defined for objects. In this case, an HMAC session should be used (see tpm2_startauthsession(1)).

🔑 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:1122334455667788

📁 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 ✨

Okay bestie, this is the part where the tools let you use "nice-names" for algorithms instead of making you hand-write cursed little numbers 💖. Two big families of algorithm strings exist: simple and complex. Heads up though — only certain algorithms get accepted by the TPM, and that depends on usage and conditions, so don't come for me if your fave gets rejected 🫶.

🌸 Simple specifiers

These are literally just strings with no extra specification data attached. When you're creating objects, any portion of the object you didn't specify gets assumed to be the defaults. The full list of known "Simple Specifiers" is right below, slay ✨.

🦋 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

So when the TPM creates an object, that object has numerous algorithms to populate in its public data — type, scheme, asymmetric details, key size, the whole main-character roster 👑. Here's the general format for spelling that out:

<type>:<scheme>:<symmetric-details>

⭐ Type Specifiers

This part of the complex algorithm specifier is required — no skipping, bestie. Everything else (the scheme and symmetric details) defaults based on the type you picked and the type of 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 up is an optional field — yes, you can literally skip it, no pressure 💜. Schemes are usually Signing Schemes or Asymmetric Encryption Schemes. Most signing schemes take a hash algorithm directly following the signing scheme, and if the hash algorithm is missing it defaults to sha256. Some take no arguments at all, and some take multiple arguments. It's giving ✨range✨.

🎀 Hash Optional Scheme Specifiers

These scheme specifiers get 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. Periodt.

  • 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 it's not specified, an asymmetric objects symmetric details defaults to aes128cfb. Iconic default behavior ngl 💅.

⭐ 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

This is the format selection for the signature output file, and yes it matters 😤. 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 is common to many programs and provides info that many users may expect. Little shared bestie starter pack, love that for us 🫶.

  • -h, --help=[man|no-man] — Display the tools manpage. By default it attempts to invoke the manpager for the tool, but on failure it'll output a short tool summary instead. Same behavior if you pass the man option argument — but if you explicitly request man, the tool will provide errors from man on stderr. If you specify the no-man option, or the manpager fails, the short options get output to stdout. To successfully use the manpages feature you need the manpages 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.

🔌 TCTI Configuration

The TCTI, or "Transmission Interface", is the communication mechanism with the TPM. TCTIs can be changed so you can talk to TPMs across different mediums — flexible queen behavior 💅.

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. No cap.

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 — very first-come-first-served of them, honestly. 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. So this could be a path to the shared library, or a library name as understood by dlopen(3) semantics. Bring your own TCTI, we love a DIY moment 🎀.

🛠️ TCTI OPTIONS

This collection of options is 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

🫶 HELP

See the Mailing List

⚖️ License

This work is licensed under the Creative Commons Attribution 4.0 International License (CC BY 4.0).

And that's the whole vibe check, bestie 💖✨ This page shipped under tpm2-tools with the manual page tag tpm2_createak(1) — go forth and create those attestation keys, you absolute icon 👑🎀

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