tpm2_getco...uditdigest(1)

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version 5.8 · 10 versions
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👑 tpm2_getcommandauditdigest(1) 👑

okay so bestie, welcome to the General Commands Manual page for tpm2_getcommandauditdigest(1) — yes that's a whole mouthful, we're gonna get through it together, i promise 💖

🌸 NAME 🌸

tpm2_getcommandauditdigest(1) — retrieve the command audit attestation data from the TPM. that's the whole vibe, that's what we're doing here ✨

✨ SYNOPSIS ✨

tpm2_getcommandauditdigest [OPTIONS]

💖 DESCRIPTION 💖

tpm2_getcommandauditdigest(1) — retrieve the command audit attestation data from the TPM. ok so what's actually in that attestation data, you ask? two things, periodt:

  • the audit digest of the commands in the setlist setup using the command tpm2_setcommandauditstatus 🔥
  • the digest of the list of commands setup for audit

and the audit digest algorithm is setup in the tpm2_setcommandauditstatus too — so if you're confused about where the algorithm comes from, that's your girl, not this one, iykyk 🫶

🎀 OPTIONS 🎀

  • -P, --hierarchy-auth=AUTH — specifies the authorization value for the endorsement hierarchy 🔐
  • -c, --key-context=OBJECT — context object for the signing key that signs the attestation data 🔑
  • -p, --auth=AUTH — specifies the authorization value for the key specified by option -c
  • -q, --qualification=HEX_STRING_OR_PATH — data given as a Hex string or binary file to qualify the quote, optional. this is typically used to add a nonce against replay attacks 🛡️ (nonce = anti-replay, iconic behaviour honestly)
  • -s, --signature=FILE — signature output file, records the signature in the format specified via the -f option ✍️
  • -m, --message=FILE — message output file, records the quote message that makes up the data that is signed by the TPM. this is the command audit digest attestation data bestie 💌
  • -f, --format=FORMAT — format selection for the signature output file
  • -g, --hash-algorithm — hash algorithm for signature. defaults to sha256 🧂
  • --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 💅

📚 REFERENCES 📚

🦋 Context Object Format 🦋

the type of a context object — whether it's a handle or a 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, and yes we're numbering them:

  1. Password
  2. HMAC
  3. Sessions
NOTE: "Authorizations default to the EMPTY PASSWORD when not specified". 🚨 like, literally empty. no cap.

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 🌈 (iconic for when your password is literally untypeable).

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 😭 so yeah, file it, don't paste it into your shell like a monster.

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. 🫶

✍️ 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 💖 (they're the little comforts, the everyday slay):

  • -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.

🌈 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. no cap, option wins, periodt 👑

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" — like, literally exactly none, bestie, no extra characters, i'm serious 💀

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 🦋

that's part 1 bestie, stay tuned 💅

💅 TCTI OPTIONS 💅

This collection of options is how you configure the various known TCTI modules that are available, bestie:

  • device: For the device TCTI, you can specify the TPM character device file that the device TCTI uses. 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 that the simulator uses. 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.
    • 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, example time — copy this exactly, bestie:

              tpm2_getcommandauditdigest -P ekpass -c key.ctx -p keypass -m att.data -s att.sig

🫶 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).

source/version: tpm2-tools · page: tpm2_getco...uditdigest(1) · date: not shown in the footer, so no invented timestamp 😭🫶💖

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