| tpm2_policypcr(1) | General Commands Manual | tpm2_policypcr(1) |
tpm2_policypcr(1) - Create a policy that includes specific PCR values.
tpm2_policypcr [OPTIONS]
tpm2_policypcr(1) - Generates a PCR policy event with the TPM. A PCR policy event creates a policy bound to specific PCR values and is useful within larger policies constructed using policyor and policyauthorize events. See tpm2_policyor(1) and tpm2_policyauthorize(1) respectively for their usages. The PCR data factored into the policy can be specified in one of 3 ways: 1. A file containing a concatenated list of PCR values as in the output from tpm2_pcrread. 2. Requiring the PCR values be read off the TPM by not specifying a PCR file input. 3. The digest of all the PCR values directly specified as an argument.
File to save the policy digest.
Optional Path or Name of the file containing expected PCR values for the specified index. Default is to read the current PCRs per the set list.
The list of PCR banks and selected PCRs’ ids for each bank.
The policy session file generated via the -S option to tpm2_startauthsession(1).
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:0x1122334455667788
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 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.
PCR Bank Selection lists follow the below specification:
<BANK>:<PCR>[,<PCR>] or <BANK>:all
multiple banks may be separated by `+'.
For example:
sha1:3,4+sha256:all
will select PCRs 3 and 4 from the SHA1 bank and PCRs 0 to 23 from the SHA256 bank.
PCR Selections allow for up to 5 hash to pcr selection mappings. This is a limitation in design in the single call to the tpm to get the pcr values. PCR.
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.
Starts a trial session, builds a PCR policy and uses that policy in the creation of an object. Then, it uses a policy session to unseal some data stored in the object.
tpm2_createprimary -C e -g sha256 -G ecc -c primary.ctx
tpm2_pcrread -o pcr.dat "sha1:0,1,2,3"
tpm2_startauthsession -S session.dat
tpm2_policypcr -S session.dat -l "sha1:0,1,2,3" -f pcr.dat -L policy.dat
tpm2_flushcontext session.dat
tpm2_create -Q -u key.pub -r key.priv -C primary.ctx -L policy.dat \
-i- <<< "12345678"
tpm2_load -C primary.ctx -u key.pub -r key.priv -n unseal.key.name \
-c unseal.key.ctx
tpm2_startauthsession --policy-session -S session.dat
tpm2_policypcr -S session.dat -l "sha1:0,1,2,3" -f pcr.dat -L policy.dat
tpm2_unseal -psession:session.dat -c unseal.key.ctx
12345678
tpm2_flushcontext session.dat
Tools can return any of the following codes:
It expects a session to be already established via tpm2_startauthsession(1) and requires one of the following:
Without it, most resource managers will not save session state between command invocations.
Github Issues (https://github.com/tpm2-software/tpm2-tools/issues)
See the Mailing List (https://lists.01.org/mailman/listinfo/tpm2)
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