tpm2_sign - Man Page

Sign a hash or message using the TPM.


tpm2_sign [Options] [ARGUMENT]


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

When signing a message, 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.



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:

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".


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.


A string password, specified by prefix "str:" or it's absence (raw string without prefix) is not interpreted, and is directly used for authorization.




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.




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.


# to use stdin and be prompted

# to use a file from a path

# 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


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.


To use a session context file called session.ctx.


To use a session context file called session.ctx AND send the authvalue mypassword.


To use a session context file called session.ctx AND send the HEX authvalue 0x11223344.


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 the output of the raw PCR contents as returned by tpm2_pcrread(1).

PCR bank specifiers (common/


To satisfy a PCR policy of sha256 on banks 0, 1, 2 and 3 use a specifier of:


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".


  • rsa
  • ecc


  • aes
  • camellia

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

Asymmetric Encryption Schemes

  • oaep
  • rsaes
  • ecdh


  • ctr
  • ofb
  • cbc
  • cfb
  • ecb


  • 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.
  • ecc - Elliptical Curve, defaults to ecc256.
  • ecc192 - 192 bit ECC
  • ecc224 - 224 bit ECC
  • ecc256 - 256 bit ECC
  • ecc384 - 384 bit ECC
  • ecc521 - 521 bit ECC
  • rsa - Default RSA: rsa2048
  • rsa1024 - RSA with 1024 bit keysize.
  • rsa2048 - RSA with 2048 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

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 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.


Create an rsa2048 key with an rsaes asymmetric encryption scheme

tpm2_create -C parent.ctx -G rsa2048:rsaes -u -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 -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.

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:

The arguments to either the command line option or the environment variable are in the form:


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:

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.


Sign and verify with the TPM using the endorsement


tpm2_createprimary -C e -c primary.ctx

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

tpm2_load -C primary.ctx -u -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

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" >

sha256sum | awk '{ print "000000 " $1 }' | \
xxd -r -c 32 >

# 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

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


Tools can return any of the following codes:


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tpm2-tools General Commands Manual