tpm2_nvincrement(1)

📦
version 5.8 · 10 versions
, in arch rolling

🎀 tpm2_nvincrement(1) — from the General Commands Manual 🎀

Bestie, this one is all about bumping a counter in a Non-Volatile (NV) index. It’s giving very specific little TPM gremlin energy, and we’re gonna keep every detail. 💅

🌟 NAME 🌟

tpm2_nvincrement(1) — Increment counter in a Non-Volatile (NV) index. ✨

🌈 SYNOPSIS 🌈

tpm2_nvincrement [OPTIONS] [ARGUMENT]

🦋 DESCRIPTION 🦋

tpm2_nvincrement(1) — Increment value of a Non-Volatile (NV) index setup as a counter. The index can be specified as raw handle or an offset value to the nv handle range “TPM2_HR_NV_INDEX”. 💖

✨ OPTIONS ✨

  • -C, --hierarchy=OBJECT — Specifies the hierarchy used to authorize. Supported options are:
    • o for TPM_RH_OWNER
    • p for TPM_RH_PLATFORM
    • <num> where a hierarchy handle or nv-index may be used.

When -C isn’t explicitly passed the index handle will be used to authorize against the index. The index auth value is set via the -p option to tpm2_nvdefine(1).

  • -P, --auth=AUTH — Specifies the authorization value for the hierarchy.
  • --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 unless rphash is also required.
  • --rphash=FILE — File path to record the hash of the response parameters. This is commonly termed as rpHash.
  • -S, --session=FILE — The session created using tpm2_startauthsession. This can be used to specify an auxiliary session for auditing and or encryption/decryption of the parameters.
  • -n, --name=FILE — The name of the NV index that must be provided when only calculating the cpHash without actually dispatching the command to the TPM.
  • ARGUMENT — the command line argument specifies the NV index or offset number.

📚 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 by 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. ⭐

🛠️ COMMON OPTIONS 🛠️

This collection of options are common to many programs and provide information that many users may expect. 😌

  • -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.

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.

🎛️ 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. 💀

✨ EXAMPLES ✨

okay so this is the part where we actually do the thing 🎀 the original page sets up a whole little counter situation at index 0x150016, so let's walk it together, bestie:

To increment the counter at index 0x150016 — here's the whole three-step glow-up, no skips:

tpm2_nvdefine -C o -s 8 -a "ownerread|authread|authwrite|nt=1" 0x1500016 -p index

tpm2_nvincrement -C 0x1500016  0x1500016 -P "index"

tpm2_nvread 0x1500016 -P index | xxd -p

first one defines the NV index (size 8, attributes ownerread|authread|authwrite|nt=1, password index), then tpm2_nvincrement bumps it, then tpm2_nvread pipes it into xxd -p so you can actually see the value. the way that pipeline just works 😭💅

ngl, copy these exactly — the index shows up as 0x150016 in the prose but 0x1500016 in the actual commands, so type what the code block says, not what the caption says 🫶

🦋 Returns 🦋

so like, what's it gonna give you back? tools can return any of the following codes, periodt:

  • 0 — success. you ate, congrats 👑
  • 1 — general non-specific error. the vague mutual-friend of errors 💀
  • 2 — options handling error. you fumbled a flag, it happens 🙈
  • 3 — authentication error. wrong password energy, the worst kind 😭
  • 4 — TCTI related error. the TCTI layer is going through something 🌧️
  • 5 — non supported scheme. applicable to tpm2_testparams 🧚

🌈 BUGS 🌈

found something cursed? it's Github Issues — that's literally where they live 🐛✨

🌸 HELP 🌸

need a human (or at least a mailing list full of them)? See the Mailing List 🫶

💜 License 💜

this work is licensed under the Creative Commons Attribution 4.0 International License (CC BY 4.0) — share it, remix it, just give the credit, iykyk 📜✨

and that's the whole page bestie, we did it 🎉 tpm2-tools brought us tpm2_nvincrement(1), and now you're basically a counter-incrementing icon. go forth and increment responsibly 💖🦋🎀

📦 where this page comes from