tpm2_sign(1)

📦
version 5.8 · 10 versions
, in arch rolling

tpm2_sign(1) — General Commands Manual 🦋

okay so this is the tpm2_sign(1) page from the General Commands Manual, and it’s literally all about signing a hash or a message with the TPM. bestie, let’s go 💅

NAME ✨

tpm2_sign(1) — Sign a hash or message using the TPM. 🎀

SYNOPSIS 🌸

tpm2_sign [OPTIONS] [ARGUMENT]

DESCRIPTION 💖

tpm2_sign(1) generates a signature of the specified message or message-digest using the specified symmetric or asymmetric signing key. 🔥

When signing a message, the tpm2_sign utility first calculates the digest of the message similar to the tpm2_hash command. It also generates a validation ticket under TPM2_RH_NULL or TPM2_RH_OWNER hierarchies respectively for unrestricted or the restricted signing keys. 👑

While signing messages is a provision in this tool, it is recommended to use the tpm2_hash tool first and pass the digest and validation ticket.

NOTE: If the signing key is a restricted signing key, then validation and digest must be provided via the -t input. The ticket indicates that the TPM performed the hash of the message. 🫶

OPTIONS 🌈

  • -c, --key-context=OBJECT — Context object pointing to the key used for signing. Either a file or a handle number. See section “Context Object Format”.
  • -p, --auth_AUTH_ — Optional authorization value to use the key specified by -c. Authorization values should follow the “authorization formatting standards”, see section “Authorization Formatting”.
  • -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.
  • -s, --scheme=ALGORITHM — The signing scheme used to sign the message. Optional. Signing schemes should follow the “formatting standards”, see section “Algorithm Specifiers”. If specified, the signature scheme must match the key type. If left unspecified, a default signature scheme for the key type will be used.
  • -d, --digest — Indicate that FILE is a file containing the digest of the message. When this option and -t is specified, a warning is generated and the validation ticket (-t) is ignored. You cannot use this option to sign a digest against a restricted signing key.
  • -t, --ticket=FILE — The ticket file, containing the validation structure, optional.
  • -o, --signature=FILE — The signature file, records the signature structure.
  • -f, --format=FORMAT — Format selection for the signature output file. See section “Signature Format Specifiers”.
  • --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.
  • --commit-index=NATURALNUMBER — The commit counter value to determine the key index to use in an ECDAA signing scheme. The default counter value is 0.
  • ARGUMENT — the command line argument specifies the file data for sign.

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 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 its 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 hexadecimal 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 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 ✨

Okay bestie, when an option wants an algorithm, it supports “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. No cap.

🌸 Simple specifiers 🌸

These are strings with no additional specification data. When creating objects, non-specified portions of an object are assumed to defaults. The known “Simple Specifiers” list is right here, bestie:

🦋 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. Slay, defaults.

  • 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 — 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 its 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. Basically, the group-chat classics. 💅

  • -h, --help=[man|no-man] — Display the tool’s 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 is 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 set to yes or true. Plus, the original also tosses in: 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. It’s giving ✨ networking but make it TPM ✨.

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. Iconic.

🦋 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. No guessing, bestie.

🦋 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. Very choose-your-own-adventure, but make it shared library. 🧚

🎀 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. And the source also says: the various known TCTI modules. 💀

⭐ Signature Format Specifiers ⭐

Format selection for the signature output file. 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. Periodt. ✨

💖 EXAMPLES 💖

okay bestie, here are the real-world recipes — copy these, don't improvise, and you'll be signing like a main character in no time ✨

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

Start with the endorsement hierarchy, make an RSA key, load it, sign a little message, then verify it. It's giving full-circle moment 🫶

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 -o sig.rssa message.dat

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

🌸 Sign with the TPM and verify with OSSL 🌸

this one is the crossover episode: TPM does the signing, OpenSSL does the verifying, and everybody eats 💅

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
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 -f plain -o data.out.signed data.in.digest

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

📋 Returns 📋

Tools can return any of the following codes — lowkey memorize these so you know what went wrong 😭

  • 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 — yes, that's literally the whole section, and honestly? iconic 👑

📣 HELP 📣

See the Mailing List — the elders have gathered, go ask them 🫶

⚖️ License ⚖️

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

mwah 💋 signed off by tpm2-tools and tpm2_sign(1), with the date chillin' in the footer like the little icon it is 🎀✨

📦 where this page comes from