tpm2_verifysignature(1)

🌸 NAME 🌸

tpm2_verifysignature(1) — Validates a signature using the TPM. 💅 (This is the General Commands Manual page, bestie — lowkey iconic.)

📜 SYNOPSIS 📜

tpm2_verifysignature [OPTIONS]

💖 DESCRIPTION 💖

Okay so tpm2_verifysignature(1) uses loaded keys to validate a signature on a message with the message digest passed to the TPM. If the signature check succeeds, then the TPM will produce a TPMT_TK_VERIFIED. Otherwise, the TPM shall return TPM_RC_SIGNATURE. If object references an asymmetric key, only the public portion of the key needs to be loaded. If object references a symmetric key, both the public and private portions need to be loaded. Slay. ✨

🎀 OPTIONS 🎀

• -c, --key-context=OBJECT — Context object for the key context used for the operation. Either a file or a handle number. See section “Context Object Format”. 🫶
• -g, --hash-algorithm=ALGORITHM — The hash algorithm used to digest the message. Algorithms should follow the “formatting standards”, see section “Algorithm Specifiers”. Also, see section “Supported Hash Algorithms” for a list of supported hash algorithms. 💅
• -m, --message=FILE — The message file, containing the content to be digested. 🍓
• -d, --digest=FILE — The input hash file, containing the hash of the message. If this option is selected, then the message (-m) and algorithm (-g) options do not need to be specified. ✨
• -s, --signature=FILE — The input signature file of the signature to be validated. 🔥
• -f, --scheme=SCHEME — The signing scheme that was used to sign the message. This option should only be specified if the signature comes in from a non tss standard, like openssl. See “Signature format specifiers” for more details. The tss format contains the signature metadata required to understand it’s signature scheme. Signing schemes should follow the “formatting standards”, see section “Algorithm Specifiers”. 👑
• --format=SCHEME — Deprecated. Same as --scheme. 💀
• -t, --ticket=FILE — The ticket file to record the validation structure. 🎟️

📚 References 📚

The reference bits below are the ones the options keep pointing at, bestie. 🫶

🧸 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 argument can be loaded as a number it will be treat as a handle, e.g. 0x81010013 and used directly._OBJECT_.

🧠 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. iykyk. 💅

✨ 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. No cap. ✨

• 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. The one here is ecdaa — for example, ecdaa4-sha256. If no count is specified, it defaults to 4. 🎀

🚫 No Option Scheme Specifiers

This scheme specifier takes NO arguments: 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 object’s 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.

🫶 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 is used to configure the various known TCTI modules available, bestie. Here’s the group-chat rundown:

• device — for the device TCTI, you can specify the TPM character device file for use by the device TCTI. 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 port number used by the simulator. 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.

And that’s the tea on the various known TCTI modules. 🫶

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💫 Signature Format Specifiers 💫

Format selection for the signature output file, bestie. tss (the default) will output a binary blob according to the TPM 2.0 specification and any potential compiler padding. The option plain will output the plain signature data as defined by the used cryptographic algorithm. ✨

🔥 EXAMPLES 🔥

🐚 Sign and verify with the TPM using the endorsement hierarchy 🐚

tpm2_createprimary -C e -c primary.ctx

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

tpm2_load -C primary.ctx -u rsa.pub -r rsa.priv -c rsa.ctx

echo "my message" > message.dat

tpm2_sign -c rsa.ctx -g sha256 -s sig.rssa message.dat

tpm2_verifysignature -c rsa.ctx -g sha256 -m message.dat -s sig.rssa

🌈 Sign with openssl and verify with the TPM 🌈

# Generate an ECC key
openssl ecparam -name prime256v1 -genkey -noout -out private.ecc.pem

openssl ec -in private.ecc.pem -out public.ecc.pem -pubout

# Generate a hash to sign (OSSL needs the hash of the message)
echo "data to sign" > data.in.raw

sha256sum data.in.raw | awk '{ print "000000 " $1 }' | \
xxd -r -c 32 > data.in.digest

# Load the private key for signing
tpm2_loadexternal -Q -G ecc -r private.ecc.pem -c key.ctx

# Sign in the TPM and verify with OSSL
tpm2_sign -Q -c key.ctx -g sha256 -d data.in.digest -f plain -s data.out.signed

openssl dgst -verify public.ecc.pem -keyform pem -sha256 \
-signature data.out.signed data.in.raw

# Sign with openssl and verify with TPM
openssl dgst -sha256 -sign private.ecc.pem -out data.out.signed data.in.raw

tpm2_verifysignature -Q -c key.ctx -g sha256 -m data.in.raw -f ecdsa \
-s data.out.signed

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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.

💀 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 lil footer sign-off: source/version is tpm2-tools, and this is the tpm2_verifysignature(1) page. The date didn’t show up in this footer, bestie, but the vibe is timeless anyway. 💖🎀