tpm2_changepps(1)

This page is tpm2_changepps(1), bestie, and it lives in the General Commands Manual. Buckle up — we’re replacing a platform seed and covering every flag, auth format, TCTI detail, return code, limitation, and license line like the organized icon you are. ✨💅

🎀 NAME 🎀

tpm2_changepps(1) — Replaces the active platform primary seed with a new one generated off the TPM2 RNG. 🦋

✨ SYNOPSIS ✨

tpm2_changepps [OPTIONS]

💖 DESCRIPTION 💖

tpm2_changepps(1) — Replaces the active platform primary seed with a new one generated off the TPM2 RNG. 🌸

⚠️ Heads up, bestie: The Transient and Persistent objects under the platform hierarchy are lost whilst retaining the NV objects. That is the whole dramatic plot twist, no cap. 😭

🌸 OPTIONS 🌸

• -p, --auth — specifies the AUTH for the platform. hierarchy. (Yes, that period is doing its own little side quest, but we keep it exactly as printed. iykyk.) 💅
• --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. 🎀

📚 References 📚

🛂 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 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. 💅

🌐 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 🔥

🔥 Change the platform primary seed where the platform auth is NULL. 🔥

tpm2_changepps

🎯 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. 😭

💀 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). 💖

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Cute sign-off time, bestie: source/version is tpm2-tools, the footer page name is tpm2_changepps(1), and the original footer didn’t print a date — so imagine a sparkly timestamp sticker right here. 🗓️✨💖