| tpm2_gettime(1) | General Commands Manual | tpm2_gettime(1) |
tpm2_gettime(1) - Get the current time and clock from the TPM in a signed form.
tpm2_gettime [OPTIONS] [ARGUMENT]
tpm2_gettime(1) - Provides a signed copy of the current time and clock from the TPM. It returns both a signature, and the data in the standard TPM attestation form, a TPMS_ATTEST structure.
It outputs to stdout, in YAML format, the TPMS_TIME_INFO structure from the TPM. The structure contains the current setting of Time, Clock, resetCount, and restartCount. The structure is output as YAML defined as:
time: 13673142 # 64 bit value of time since last _TPM_Init or TPM2_Startup
# in ms. clock_info:
clock: 13673142 # 64 bit value of time TPM has been powered on in ms.
reset_count: 0 # 32 bit value of the number of TPM Resets since the last
# TPM2_Clear.
restart_count: 0 # 32 bit value of the number of times that TPM2_Shutdown or
# _TPM_Hash_Start have occurred since the last TPM Reset or
# TPM2_Clear.
safe: yes # boolean yes|no value that no value of Clock greater than
# the current value of Clock has been previously reported by
# the TPM.
Context object pointing to the the key used for signing. Either a file or a handle number. See section “Context Object Format”.
Optional authorization value to use the key specified by -c. Authorization values should follow the “authorization formatting standards”, see section “Authorization Formatting”.
Optional authorization value for the endorsement hierarchy. Authorization values should follow the “authorization formatting standards”, see section “Authorization Formatting”.
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.
The signing scheme used to sign the message. Optional. Signing schemes should follow the “formatting standards”, see section “Algorithm Specifiers”. Also, see section “Supported Signing Schemes” for a list of supported signature schemes. If specified, the signature scheme must match the key type. If left unspecified, a default signature scheme for the key type will be used.
Optional, the policy qualifier data that the signer can choose to include in the signature. Can be either a hex string or path.
The signature file, records the signature structure.
Format selection for the signature output file. See section “Signature Format Specifiers”.
The attestation data of the type TPMS_ATTEST signed with signing key.
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.
The type of a context object, whether it is a handle or file name, is determined according to the following logic in-order:
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.
foobar
str:foobar
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.
hex:1122334455667788
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
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
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.
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
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
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.
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.
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.
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>
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.
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.
These scheme specifiers are followed by a dash and a valid hash algorithm, For example: oaep-sha256.
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.
This scheme specifier takes NO arguments. * rsaes
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.
tpm2_create -C parent.ctx -G rsa2048:rsaes -u key.pub -r key.priv
/tpm2_create -C parent.ctx -G ecc256:ecdaa4-sha384 -u key.pub -r key.priv cryptographic algorithms ALGORITHM.
This collection of options are common to many programs and provide information that many users may expect.
To successfully use the manpages feature requires the manpages to be installed or on MANPATH, See man(1) for more details.
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:
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.
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.
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.
This collection of options are used to configure the various known TCTI modules available:
Example: -T device:/dev/tpm0 or export TPM2TOOLS_TCTI=“device:/dev/tpm0”
Example: -T mssim:host=localhost,port=2321 or export TPM2TOOLS_TCTI=“mssim:host=localhost,port=2321”
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 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.
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
tpm2_gettime -c rsa.ctx -o attest.sig --attestation attest.data
Tools can return any of the following codes:
Github Issues (https://github.com/tpm2-software/tpm2-tools/issues)
See the Mailing List (https://lists.linuxfoundation.org/mailman/listinfo/tpm2)
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