tpm2_pcrevent(1)

📦
version 5.8 · 10 versions
, in arch rolling

💅 tpm2_pcrevent(1) — the girlies' guide to pcr eventing 🌸

okay so real talk, this page? it's from General Commands Manual and the tool is literally called tpm2_pcrevent(1) and it ATE. it hashes stuff and optionally extends a PCR and honestly it's giving main character energy 🎀

✨ NAME ✨

tpm2_pcrevent(1) — hashes a file and, like, optionally extends a pcr. lowkey iconic.

🦋 SYNOPSIS 🦋

tpm2_pcrevent [OPTIONS] FILE PCR_INDEX

💖 DESCRIPTION 💖

okay bestie, listen up 💅 tpm2_pcrevent(1) hashes FILE if you give it one, or stdin if you don't. and the way it does this? it uses all of the hashing algorithms that the TPM supports. like, all of them. no cap. 🔥

optionally, if you specify a PCR index, it extends that PCR for all supported algorithms with the hash digest. and here's the cute part: FILE and _PCR_INDEX_ arguments don't need to come in any particular order. slay, we love a flexible queen 🫶

in either case, it outputs to stdout the hash algorithm used and the digest value, one per line, like this:

alg:digest

where alg is the algorithm used (like sha1) and digest is the digest resulting from the hash computation of alg on the data. iykyk ⭐

see sections 23.1 and sections 17 of the TPM2.0 Specification 📖

🌈 OPTIONS 🌈

these options control extending the pcr, bestie:

  • -P, --auth=AUTH — specifies the authorization value for PCR. that's the vibe check for who's allowed in 💅
  • -S, --session=FILE — specifies the auxiliary sessions for the command. sessions, plural, we're fancy 🎀
  • --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. so like... it's the trailer not the movie 🙈

References

(move along, nothing to see here, the manpage said "References" and who am I to argue 💀)

👑 COMMON OPTIONS 👑

this collection of options are common to many programs and provide information that many users may expect. the communal wardrobe of flags, basically 🧚

  • -h, --help=[man|no-man] — display the tool's manpage. by default it attempts to invoke the manpager for the tool, but on failure will output a short tool summary. 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 is 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. fr fr, read the docs about reading the docs 📚

  • -v, --version — display version information for this tool, supported tctis and exit. short and sweet, love that for us ✨
  • -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. she's nosy and we respect it 💅
  • -Q, --quiet — silence normal tool output to stdout. shhh 🤫
  • -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. ⚠️ note the caveat, bestie, clear text is clear text
  • -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. (yes the original says "is is", we're keeping it, it's canon 💀) 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. it's the group chat your tool uses to reach the TPM 📱

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. 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, exact exact 🫠

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. no stress 💜

🎀 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. she picks her fave and commits 💅

🦋 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. bring your own TCTI to the party 🎉

🌸 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. (yes, that trailing fragment is literally in the original, we don't gatekeep 💀)

🔐 Authorization Formatting 🔐

authorization for use of an object in TPM2.0 can come in 3 different forms: 1. Password 2. HMAC 3. Sessions. pick your fighter ✨

NOTE: "Authorizations default to the EMPTY PASSWORD when not specified". so if you skip it, it's 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)). read that one too bestie, it's a whole thing 📖

🍓 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. she's authentic, no filter 💅

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. for the girlies whose passwords are literally bytes 🫶

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. 🔥 big security slay, do this one

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. the + is doing SO much work 💜

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". (again, "in in", iconic, we keep it 💀)

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

🌟 EXAMPLES 🌟

Hash a file

echo "foo" > data
tpm2_pcrevent data

Hash a file and extend PCR 8

echo "foo" > data
tpm2_pcrevent 8 data

(yeah, the args are flipped in that second one — that's literally the point, order doesn't matter, she's flexible 🫶)

💀 Returns 💀

tools can return any of the following codes:

  • 0 — Success. we love a win ✨
  • 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). slay, and legally so 💅

okay that's the whole page bestie, go extend some PCRs responsibly 🦋 and yeah — this was tpm2-tools, page tpm2_pcrevent(1), mwah, bye 👑💖

📦 where this page comes from