tpm2_activatecredential(1)

📦
version 5.8 · 10 versions
, in arch rolling

💖 NAME 💖

tpm2_activatecredential(1) — bestie, this is the tool that enables access to the credential qualifier so you can recover the credential secret. That's the whole vibe. ✨

(And yes, this is the tpm2_activatecredential(1) man page, General Commands Manual energy, we're doing this.)

🦋 SYNOPSIS 🦋

tpm2_activatecredential [OPTIONS]

That's it. Just vibes and options. 💅

🌸 DESCRIPTION 🌸

Okay so listen 👑 — tpm2_activatecredential(1) enables the association of a credential with an object in a way that ensures that the TPM has validated the parameters of the credentialed object.

In an attestation scheme, this guarantees the registrar that the attestation key belongs to the TPM with a qualified parent key in the TPM. No cap, that's literally the point. It's giving trust-but-verified, it's giving "the TPM said so," it's iconic. 🎀

✨ OPTIONS ✨

  • -c, --credentialedkey-context=OBJECT — the object associated with the created certificate by CA. 🫶
  • -C, --credentialkey-context=OBJECT — the loaded object used to decrypt the random seed.
  • -p, --credentialedkey-auth=AUTH — the auth value of the credentialed object specified with -c.
  • -P, --credentialkey-auth=AUTH — the auth value of the credential object specified with -C. (yes, the capital-vs-lowercase thing is a whole moment, keep up bestie 😭)
  • -i, --credential-blob=FILE — the input file path containing the credential blob and secret created with the tpm2_makecredential(1) tool. 🍓
  • -o, --certinfo-data=FILE — the output file path to save the decrypted credential secret information.
  • --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 🌈

💜 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 can be loaded as a number it will be treated 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 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 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.
Heads up bestie: clear text password = it is what it says on the tin. 👀
  • -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 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. 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”. 💀

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

Okay so this cluster of options is all about configuring the different known TCTI modules — that's your Transport Layer, the thing that actually lets the tools talk to a TPM. Pick your fighter:

  • device — for the device TCTI, you can point at the exact TPM character device file you want it to use. 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 the port number your simulator is chilling on. 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 config string format is a series of simple key-value pairs, separated by a , character. Each key and its value are separated by a = character.
    • The 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 plus a config string of bus_name=com.example.FooBar:

\--tcti=tabrmd:bus_name=com.example.FooBar

Specify the default (abrmd) tcti plus a config string of bus_type=session:

\--tcti:bus_type=session
NOTE: abrmd and tabrmd are synonymous. 💅 (yes, the original manpage ends that sentence with "the various known TCTI modules." — we're leaving that little fragment exactly where it is, no cap, it's iconic in a chaotic way)

🌸 EXAMPLES

Okay bestie, here's the whole glow-up routine start to finish — copying it exactly because every character matters:

       echo "12345678" > secret.data

       tpm2_createek -Q -c 0x81010001 -G rsa -u ek.pub

       tpm2_createak -C 0x81010001 -c ak.ctx -G rsa -g sha256 -s rsassa -u ak.pub \
       -n ak.name -p akpass> ak.out

       file_size=`stat --printf="%s" ak.name`
       loaded_key_name=`cat ak.name | xxd -p -c $file_size`

       tpm2_makecredential -Q -e ek.pub  -s secret.data -n $loaded_key_name \
       -o mkcred.out

       tpm2_startauthsession --policy-session -S session.ctx

       tpm2_policysecret -S session.ctx -c e

       tpm2_activatecredential -Q -c ak.ctx -C 0x81010001 -i mkcred.out \
       -o actcred.out -p akpass -P"session:session.ctx"

       tpm2_flushcontext session.ctx

🎯 Returns

Tools can return any of the following codes, bestie — memorise the vibe check:

  • 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 — that's where the bugs live, go yell there (politely!).

🫶 HELP

See the Mailing List.

👑 License

This work is licensed under the Creative Commons Attribution 4.0 International License (CC BY 4.0).

Aaaand that's the whole page, babes! ✨ This one's tpm2_activatecredential(1), coming to you from tpm2-tools in the General Commands Manual section — flip to the very last line of the page for the source/version and date stamp, because that footer is the main character and it deserves its moment. 🎀 Go forth and activate those credentials, iykyk 💜🦋

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