tpm2_policyor(1)

📦
version 5.8 · 10 versions
, in arch rolling

💅 tpm2_policyor — the General Commands Manual glow-up 🎀

okay so bestie, welcome to tpm2_policyor(1), straight out of your friendly neighborhood General Commands Manual ✨. Grab a lil snack, we're gonna OR some policies together and it's gonna be iconic.

✨ NAME ✨

tpm2_policyor(1) — logically OR's two policies together. yeah. that's the whole vibe. two policies, one OR, slay 💅

🌸 SYNOPSIS 🌸

tpm2_policyor [OPTIONS]

like, that's it. options only. no cap.

🦋 DESCRIPTION 🦋

So tpm2_policyor(1) generates a policy_or event with the TPM. Important first thing: it expects a session to be already established via tpm2_startauthsession(1) — you cannot just walk in here with no session, that's not the move 🙈.

Now here's the tea, and it depends on what kind of session you brought:

  • If the input session is a trial session, this tool generates a policy digest that compounds two or more input policy digests such that the resulting policy digest requires at least one of the policy events being true. 🔥
  • If the input session is a real policy session, tpm2_policyor(1) authenticates the object successfully if at least one of the policy events are true. ✅

Either way, "at least one" is the whole point — it's an OR, bestie, not an AND 💖

💜 OPTIONS 💜

  • -L, --policy=FILE — File to save the compounded policy digest. this is where the magic gets written down 🫶
  • -S, --session=FILE — The policy session file generated via the -S option to tpm2_startauthsession(1). bring your own session, iykyk.
  • ARGUMENT — the command line argument specifies the list of files for the policy digests that has to be compounded resulting in individual policies being added to final policy digest that can authenticate the object. The list begins with the policy digest hash alg. Example sha256:policy1,policy2 ⭐
ngl, the argument method is the one you should be using. it's giving main character energy.
  • -l, --policy-list=POLICY_FILE_LIST — This option is DEPRECATED yet is retained for backwards compatibility. Use the argument method instead. 💀
NOTE: When -l and an argument is specified it's the same as specifying it all at once. For instance: tpm2_policyor -l sha256:file1 sha256:file2 is the same as tpm2_policyor sha256:file1,file2.

References

(that's it. that's the section. the original said "References" and then moved on, so we move on too 💫)

🌈 COMMON OPTIONS 🌈

This collection of options are common to many programs and provide information that many users may expect. your old reliable besties, fr fr.

  • -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. cute AND informative.
  • -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 chatty and we love that 💬
  • -Q, --quiet — Silence normal tool output to stdout. shhhh 🤫
  • -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.
okay real talk: "clear text password is passed to the TPM" — that's the actual documented behavior, so know that going in 👀
  • -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. it's basically 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. don't argue with her, she's right.

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. go off, custom TCTI 👑

🎀 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, the original really ends that sentence like that. we're keeping it. 💅)

🔥 EXAMPLES 🔥

Create an authorization policy for a sealing object that compounds a pcr policy and a policypassword in an OR fashion and show satisfying either policies could unseal the secret. this is the whole demo, bestie, watch and learn 🌸

Create policypcr as first truth value for compounding the policies

tpm2_startauthsession -S session.ctx
tpm2_policypcr -S session.ctx -L policy.pcr -l sha256:0,1,2,3
tpm2_flushcontext session.ctx

Create policypassword as second truth value for compounding the policies

tpm2_startauthsession -S session.ctx
tpm2_policypassword -S session.ctx -L policy.pass
tpm2_flushcontext session.ctx

Compound the two policies in an OR fashion with tpm2_policyor command

tpm2_startauthsession -S session.ctx
tpm2_policyor -S session.ctx -L policy.or sha256:policy.pass,policy.pcr
tpm2_flushcontext session.ctx

Create a sealing object and attach the auth policy from tpm2_policyor command

tpm2_createprimary -c prim.ctx -Q
echo "secret" | tpm2_create -C prim.ctx -c key.ctx -u key.pub -r key.priv \
-L policy.or -i-

Satisfy auth policy using password and unseal the secret

tpm2_startauthsession -S session.ctx --policy-session
tpm2_policypassword -S session.ctx
tpm2_policyor -S session.ctx sha256:policy.pass,policy.pcr
tpm2_unseal -c key.ctx -p session:session.ctx
tpm2_flushcontext session.ctx

Satisfy auth policy using pcr and unseal the secret

tpm2_startauthsession -S session.ctx --policy-session
tpm2_policypcr -S session.ctx -l sha256:0,1,2,3
tpm2_policyor -S session.ctx sha256:policy.pass,policy.pcr
tpm2_unseal -c key.ctx -p session:session.ctx
tpm2_flushcontext session.ctx

see how either path gets you the secret? that's the OR doing its thing. iconic behavior honestly 🙌

⭐ 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.

💀 Limitations 💀

It expects a session to be already established via tpm2_startauthsession(1) and requires one of the following:

  • direct device access
  • extended session support with tpm2-abrmd.
Without it, most resource managers will not save session state between command invocations. so like… don't skip this part, bestie 😭

🙈 BUGS 🙈

Github Issues.

(that's the whole section. she's brief. we respect it.)

👑 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 page!! ✨ this lil beauty comes to you from tpm2-tools and the page itself is dated/versioned right there in the footer as tpm2_policyor(1) — so go forth, compound those policies, and unseal your secrets. mwah 💖🎀🦋

📦 where this page comes from