tpm2_nvcertify(1)

🌸 NAME 🌸

okay so bestie, this is tpm2_nvcertify(1) — and she is literally here to provide attestation of the contents of an NV index. 🫶 That's the whole vibe: she certifies what's inside an NV index, and the output reveals the NV index contents as part of the attestation. Iconic, but also eyes open, iykyk.

✨ SYNOPSIS ✨

tpm2_nvcertify [OPTIONS] [ARGUMENTS]

🦋 DESCRIPTION 🦋

tpm2_nvcertify(1) — Provides attestation of the contents of an NV index. That's her main character job, periodt. 💅

⚠️ NOTE: As part of the attestation output, the NV index contents are revealed. So yeah, the tea is spilled in the output — no cap.

💅 OPTIONS 💅

These options control the certification:

• -C, --signingkey-context=OBJECT — the key object that signs the attestation structure. She's the signer, the one with the pen, fr fr.
• -P, --signingkey-auth=AUTH — the authorization value provided for the object specified with -C.
• -c, --nvauthobj-context=OBJECT — the object that is the authorization handle for the NV object. It is either the NV index handle itself or the platform/ owner hierarchy handle. If not specified it defaults to the NV index handle.
• -p, --nvauthobj-auth=AUTH — the authorization value provided for the object specified with -c.
• -g, --hash-algorithm=ALGORITHM — the hash algorithm to use in signature generation.
• -s, --scheme=ALGORITHM — the signing scheme used to sign the attestation data.
• -f, --format=FORMAT — format selection for the signature output file.
• -o, --signature=FILE — output file name for the signature data.
• -q, --qualification=FILE_OR_HEX_STR — Optional, the policy qualifier data that the signer can choose to include in the signature. Can be either a hex string or path.
• --size=NATURAL_NUMBER — Specifies the size of data to be read in bytes, starting from 0 if offset is not specified. If not specified, the size of the data as reported by the public portion of the index will be used.
• --offset=NATURAL_NUMBER — The offset within the NV index to start reading from.
• –attestation=FILE — The attestation data of the type TPMS_ATTEST signed with signing key.
• --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.
• -signer-name=FILE — The name of the signing key 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 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.

🔥 Algorithm Specifiers 🔥

Options that take algorithms support “nice-names”.

There are two major algorithm specification string classes, simple and complex. Only certain algorithms will be accepted by the TPM, based on usage and conditions.

Simple specifiers

These are strings with no additional specification data. When creating objects, non-specified portions of an object are assumed to defaults. You can find the list of known “Simple Specifiers” below.

Asymmetric

• rsa
• ecc

Symmetric

• aes
• camellia
• sm4

Hashing Algorithms

• sha1
• sha256
• sha384
• sha512
• sm3_256
• sha3_256
• sha3_384
• sha3_512

Keyed Hash

• hmac
• xor

Signing Schemes

• rsassa
• rsapss
• ecdsa
• ecdaa
• ecschnorr
• sm2

Asymmetric Encryption Schemes

• oaep
• rsaes
• ecdh

Modes

• ctr
• ofb
• cbc
• cfb
• ecb

Misc

• null

Complex Specifiers

Objects, when specified for creation by the TPM, have numerous algorithms to populate in the public data. Things like type, scheme and asymmetric details, key size, etc. Below is the general format for specifying this data:

<type>:<scheme>:<symmetric-details>

Type Specifiers

This portion of the complex algorithm specifier is required. The remaining scheme and symmetric details will default based on the type specified and the type of the object being created.

• aes — Default AES: aes128
• aes128<mode> — 128 bit AES with optional mode (ctr|ofb|cbc|cfb|ecb). If mode is not specified, defaults to null.
• aes192<mode> — Same as aes128<mode>, except for a 192 bit key size.
• aes256<mode> — Same as aes128<mode>, except for a 256 bit key size.
• sm4 — Default SM4: sm4128
• sm4128 or sm4_128 <mode> — 128 bit SM4 with optional mode (ctr|ofb|cbc|cfb|ecb). If mode is not specified, defaults to null.
• ecc — Elliptical Curve, defaults to ecc256.
• ecc192 or ecc_nist_p192 — 192 bit ECC NIST curve
• ecc224 or ecc_nist_p224 — 224 bit ECC NIST curve
• ecc256 or ecc_nist_p256 — 256 bit ECC NIST curve
• ecc384 or ecc_nist_p384 — 384 bit ECC NIST curve
• ecc521 or ecc_nist_p521 — 521 bit ECC NIST curve
• ecc_sm2 or ecc_sm2_p256 — 256 bit SM2 curve
• rsa — Default RSA: rsa2048
• rsa1024 — RSA with 1024 bit keysize.
• rsa2048 — RSA with 2048 bit keysize.
• rsa3072 — RSA with 3072 bit keysize.
• rsa4096 — RSA with 4096 bit keysize.

Scheme Specifiers

Next, is an optional field, it can be skipped.

Schemes are usually Signing Schemes or Asymmetric Encryption Schemes. Most signing schemes take a hash algorithm directly following the signing scheme. If the hash algorithm is missing, it defaults to sha256. Some take no arguments, and some take multiple arguments.

Hash Optional Scheme Specifiers

These scheme specifiers are followed by a dash and a valid hash algorithm, For example: oaep-sha256.

• oaep
• ecdh
• rsassa
• rsapss
• ecdsa
• ecschnorr
• sm2

Multiple Option Scheme Specifiers

This scheme specifier is followed by a count (max size UINT16) then followed by a dash(-) and a valid hash algorithm. ecdaa is the one in this list — for example, ecdaa4-sha256. If no count is specified, it defaults to 4.

No Option Scheme Specifiers

This scheme specifier takes NO arguments. The one here is rsaes.

Symmetric Details Specifiers

This field is optional, and defaults based on the type of object being created and it’s attributes. Generally, any valid Symmetric specifier from the Type Specifiers list should work. If not specified, an asymmetric objects symmetric details defaults to aes128cfb.

Examples

Create an rsa2048 key with an rsaes asymmetric encryption scheme

tpm2_create -C parent.ctx -G rsa2048:rsaes -u key.pub -r key.priv

Create an ecc256 key with an ecdaa signing scheme with a count of 4 and sha384 hash

/tpm2_create -C parent.ctx -G ecc256:ecdaa4-sha384 -u key.pub -r key.priv cryptographic algorithms ALGORITHM.

✨ Signature Format Specifiers ✨

This is the vibe check for your signature output file, bestie. 💅 tss — the default — outputs a binary blob according to the TPM 2.0 specification and any potential compiler padding. The plain option outputs the plain signature data as defined by the used cryptographic algorithm. That's the whole signature FORMAT moment. 🎀

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💖 COMMON OPTIONS 💖

This collection of options is common to many programs and provides information that many users may expect. (Yes, the original really says that — we love a shared-options era. 😌)

• -h, --help=[man|no-man] — Display the tool's manpage. By default it attempts to invoke the manpager for the tool, but on failure it outputs a short tool summary. Same behavior if the man option argument is specified, except if explicit man is requested, the tool provides errors from man on stderr. If the no-man option is specified, or the manpager fails, the short options are output to stdout. To successfully use the manpages feature, the manpages need 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 the tool prints to the console during 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 variable TPM2TOOLS_ENABLE_ERRATA is equivalent. 🛠️
• -z, --pwd-session — Use a 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 set to yes or true. (The original bullet also trails off with “information many users may expect.” — iconic copy-paste ghost, but we keep it. 👻)

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🌈 TCTI Configuration 🌈

The TCTI, aka “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. No cap. 💅

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 initialize 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 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 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 indicates 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. So this could be a path to the shared library, or a library name as understood by dlopen(3) semantics. 🪄

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💅 TCTI OPTIONS 💅

This collection of options is 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 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 configuration string format is a series of simple key-value pairs separated by a , character. Each key and value string are separated by an = 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 original page also ends this section with the stray fragment “the various known TCTI modules.” — we keep the crumbs. 💀

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⭐ EXAMPLES ⭐

tpm2_nvdefine -s 32 -a "authread|authwrite" 1

dd if=/dev/urandom bs=1 count=32 status=none| \
tpm2_nvwrite 1 -i-

tpm2_createprimary -C o -c primary.ctx -Q

tpm2_create -G rsa -u rsa.pub -r rsa.priv -C primary.ctx -c signing_key.ctx -Q

tpm2_readpublic -c signing_key.ctx -f pem -o sslpub.pem -Q

tpm2_nvcertify -C signing_key.ctx -g sha256 -f plain -s rsassa \
-o signature.bin --attestation attestation.bin --size 32 1

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😭 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.

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💀 BUGS 💀

Github Issues

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🫶 HELP 🫶

See the Mailing List

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🎀 License 🎀

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

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Later bestie! 💖 This page's source/version footer stamps it as tpm2-tools and tpm2_nvcertify(1), with the date living in the footer like a good little manual page. 🌸✨