tpm2_verifysignature - Man Page

Validates a signature using the TPM.

Synopsis

tpm2_verifysignature [Options]

Description

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.

Options

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:

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 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.

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.

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:

<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 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.

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

Returns

Tools can return any of the following codes:

Bugs

Github Issues (https://github.com/tpm2-software/tpm2-tools/issues)

Help

See the Mailing List (https://lists.linuxfoundation.org/mailman/listinfo/tpm2)

Referenced By

tpm2_policyauthorize(1).

tpm2-tools General Commands Manual