tpm2_gettime(1)

📦
version 5.8 · 10 versions
, in arch rolling

🌸 NAME 🌸

tpm2_gettime(1) — get the current time and clock from the TPM in a signed form. This one is from the General Commands Manual, bestie. 💅

✨ SYNOPSIS ✨

tpm2_gettime [OPTIONS] [ARGUMENT]

💖 DESCRIPTION 💖

Okay so tpm2_gettime(1) gives you a signed copy of the current time and clock from the TPM. It returns both a signature, and the data in the standard TPM attestation form, a TPMS_ATTEST structure. Iconic behavior, honestly. 🫶

It outputs to stdout, in YAML format, the TPMS_TIME_INFO structure from the TPM. That structure contains the current setting of Time, Clock, resetCount, and restartCount. The structure is output as YAML defined as:

time: 13673142     # 64 bit value of time since last _TPM_Init or TPM2_Startup
                   # in ms.
clock_info:
  clock: 13673142  # 64 bit value of time TPM has been powered on in ms.
  reset_count: 0   # 32 bit value of the number of TPM Resets since the last
                   # TPM2_Clear.
  restart_count: 0 # 32 bit value of the number of times that TPM2_Shutdown or
                   # _TPM_Hash_Start have occurred since the last TPM Reset or
                   # TPM2_Clear.
  safe: yes        # boolean yes|no value that no value of Clock greater than
                   # the current value of Clock has been previously reported by
                   # the TPM.

🎀 OPTIONS 🎀

  • -c, --key-context=OBJECT — context object pointing to the key used for signing. Either a file or a handle number. See section “Context Object Format”.
  • -p, --auth_AUTH_ — optional authorization value to use the key specified by -c. Authorization values should follow the “authorization formatting standards”, see section “Authorization Formatting”.
  • -P, --endorse-auth_AUTH_ — optional authorization value for the endorsement hierarchy. Authorization values should follow the “authorization formatting standards”, see section “Authorization Formatting”.
  • -g, --hash-algorithm=ALGORITHM — the hash algorithm used to digest the message. Algorithms should follow the “formatting standards”, see section “Algorithm Specifiers”. Also, see section “Supported Hash Algorithms” for a list of supported hash algorithms.
  • -s, --scheme=ALGORITHM — the signing scheme used to sign the message. Optional. Signing schemes should follow the “formatting standards”, see section “Algorithm Specifiers”. Also, see section “Supported Signing Schemes” for a list of supported signature schemes. If specified, the signature scheme must match the key type. If left unspecified, a default signature scheme for the key type will be used.
  • -q, --qualification=FILE_OR_HEX_STR — optional, the policy qualifier data that the signer can choose to include in the signature. Can be either a hex string or path.
  • -o, --signature=FILE — the signature file, records the signature structure.
  • -f, --format=FORMAT — format selection for the signature output file. See section “Signature Format Specifiers”.
  • –attestation=FILE — the attestation data of the type TPMS_ATTEST signed with signing key.
  • --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.
  • ARGUMENT — the command line argument specifies the file data for sign.

🫶 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 its 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 so options that take algorithms? They're totally chill with "nice-names" 💅 like, you don't have to pass a raw number, you can just say rsa and it gets you.

There are two big algorithm specification string classes: simple and complex. Lowkey important: only certain algorithms will actually be accepted by the TPM, depends on usage and conditions. So no cap, the TPM has opinions 💀

Simple specifiers

These are strings with no extra specification data. When you're creating objects, the non-specified parts of an object are just assumed to be the defaults. The whole "Simple Specifiers" guest list is right below, bestie 👇

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 objects get specified for creation by the TPM, they've got a whole bunch of algorithms to populate in the public data — type, scheme, asymmetric details, key size, all of it. The general format for specifying all this is:

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

Type Specifiers

This part of the complex algorithm specifier is required (no skipping, it's the main character ✨). The remaining scheme and symmetric details will default based on whatever type you specified 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: an optional field, so you can literally just skip it if you want 🦋

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. It's giving ✨range✨

Hash Optional Scheme Specifiers

These ones 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 object's 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.
Ngl that trailing cryptographic algorithms ALGORITHM. and the leading / are literally what's sitting in the page — I'm not touching them, they're canon 🫶

🌸 COMMON OPTIONS 🌸

This collection of options is common to many programs and hands over info that lots of users probably expect already.

  • -h, --help=[man|no-man] — Display the tool's manpage. By default it tries to invoke the manpager for the tool, but on failure it'll output a short tool summary. Same behavior if you pass the man option argument — except if you explicitly ask for man, the tool will hand you errors from man on stderr. If you specify the no-man option, or the manpager just flops, 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 info the tool prints to the console during its execution. When using this option the file and line number are printed. (obsessed with this one tbh 🔥)
  • -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 variable TPM2TOOLS_ENABLE_ERRATA is equivalent.
  • -z, --pwd-session — Use a 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 swapped out for talking to TPMs across different mediums. Very main character energy of them 💅

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 exceptions, bestie.

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 you try to use them without a TCTI connection. Does not support ANY options and MUST BE presented as the exact text of none. (like, exactly. don't get cute.)

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 isn't specified, the default TCTI is searched for using dlopen(3) semantics. The tools 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. So this could be a path to the shared library, or a library name as understood by dlopen(3) semantics. slay, flexible 💖

🎀 TCTI OPTIONS 🎀

This collection of options is used to configure the various known TCTI modules available:

  • device — For the device TCTI, you can specify the TPM character device file for the device TCTI to use. The default is /dev/tpm0.

Example: -T device:/dev/tpm0 or export TPM2TOOLS_TCTI="device:/dev/tpm0"

  • mssim — For the mssim TCTI, you can specify the domain name or IP address and port number used by the simulator. The defaults 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.
    • The 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.

⭐ 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. pick your fighter 💅

🌈 EXAMPLES 🌈

Create a key and get attested TPM time

tpm2_createprimary -C e -c primary.ctx

tpm2_create -G rsa -u rsa.pub -r rsa.priv -C primary.ctx

tpm2_load -C primary.ctx -u rsa.pub -r rsa.priv -c rsa.ctx

tpm2_gettime -c rsa.ctx -o attest.sig --attestation attest.data

💜 Returns 💜

Tools can return any of the following codes:

  • 0 — Success. (we love to see it 🎉)
  • 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 page, bestie — you ate that 💅✨ It's from tpm2-tools, page tpm2_gettime(1), and that's the footer, cute little sign-off and everything 🎀

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