| tpm2_duplicate(1) | General Commands Manual | tpm2_duplicate(1) |
tpm2_duplicate(1) - Duplicates a loaded object so that it may be used in a different hierarchy.
tpm2_duplicate [OPTIONS]
tpm2_duplicate(1) - This tool duplicates a loaded object so that it may be used in a different hierarchy. The new parent key for the duplicate may be on the same or different TPM or TPM_RH_NULL.
These options control the key importation process:
The symmetric algorithm to be used for the inner wrapper. Supports:
Specifies the filename of the symmetric key (128 bit data) to be used for the inner wrapper. Valid only when specified symmetric algorithm is not null
Specifies the filename to store the symmetric key (128 bit data) that was used for the inner wrapper. Valid only when specified symmetric algorithm is not null and --input-key-file is not specified. The TPM generates the key in this case.
The parent key object.
Specifies the file path to save the private portion of the duplicated object. # Protection Details
Objects that can move outside of TPM need to be protected (confidentiality and integrity). For instance, transient objects require that TPM protected data (key or seal material) be stored outside of the TPM. This is seen in tools like tpm2_create(1), where the -r option outputs this protected data. This blob contains the sensitive portions of the object. The sensitive portions of the object are protected by the parent object, using the parent’s symmetric encryption details to encrypt the sensitive data and HMAC it.
In-depth details can be found in sections 23 of:
Notably Figure 20, is relevant, even though it’s specifically referring to duplication blobs, the process is identical.
If the output is from tpm2_duplicate(1), the output will be slightly different, as described fully in section 23.
The file to save the encrypted seed of the duplicated object.
The authorization value for the key, optional.
The object to be duplicated.
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: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.
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.
To duplicate a key, one needs the key to duplicate, created with a policy that
allows duplication and a new parent:
tpm2_startauthsession -S session.dat
tpm2_policycommandcode -S session.dat -L policy.dat TPM2_CC_Duplicate
tpm2_flushcontext session.dat
tpm2_createprimary -C o -g sha256 -G rsa -c primary.ctxt
tpm2_create -C primary.ctxt -g sha256 -G rsa -r key.prv -u key.pub \
-L policy.dat -a "sensitivedataorigin"
tpm2_loadexternal -C o -u new_parent.pub -c new_parent.ctxt
tpm2_startauthsession \--policy-session -S session.dat
tpm2_policycommandcode -S session.dat -L policy.dat TPM2_CC_Duplicate
tpm2_duplicate -C new_parent.ctxt -c key.ctxt -G null -p "session:session.dat" \
-r duprv.bin -s seed.dat
tpm2_flushcontext session.dat
As an end-to-end example, the following will transfer an RSA key generated on TPM-A to TPM-B
Create a parent object that will be used to wrap/transfer the key.
tpm2_createprimary -C o -g sha256 -G rsa -c primary.ctx
tpm2_create -C primary.ctx -g sha256 -G rsa \
-r new_parent.prv -u new_parent.pub \
-a "restricted|sensitivedataorigin|decrypt|userwithauth"
Copy new_parent.pub to TPM-A.
Create root object and auth policy allows duplication only
tpm2_createprimary -C o -g sha256 -G rsa -c primary.ctx
tpm2_startauthsession -S session.dat
tpm2_policycommandcode -S session.dat -L dpolicy.dat TPM2_CC_Duplicate
tpm2_flushcontext session.dat
rm session.dat
Generate an RSA keypair on TPM-A that will be duplicated (note the passphrase is `foo')
tpm2_create -C primary.ctx -g sha256 -G rsa -p foo -r key.prv \
-u key.pub -L dpolicy.dat -a "sensitivedataorigin|userwithauth|decrypt|sign"
tpm2_load -C primary.ctx -r key.prv -u key.pub -c key.ctx
tpm2_readpublic -c key.ctx -o dup.pub
Test sign and encryption locally (so we can compare later that the same key was transferred).
echo "meet me at.." >file.txt
tpm2_rsaencrypt -c key.ctx -o data.encrypted file.txt
tpm2_sign -c key.ctx -g sha256 -f plain -p foo -o sign.raw file.txt
Compare the signature hash (we will use this later to confirm the key was transferred to TPM-B):
sha256sum sign.raw
a1b4e3fbaa29e6e46d95cff498150b6b8e7d9fd21182622e8f5a3ddde257879e
Start an auth session and policy command to allow duplication
tpm2_startauthsession --policy-session -S session.dat
tpm2_policycommandcode -S session.dat -L dpolicy.dat TPM2_CC_Duplicate
Load the new_parent.pub file transferred from TPM-B
tpm2_loadexternal -C o -u new_parent.pub -c new_parent.ctx
Start the duplication
tpm2_duplicate -C new_parent.ctx -c key.ctx -G null \
-p "session:session.dat" -r dup.dpriv -s dup.seed
Copy the following files to TPM-B: * dup.pub * dup.dpriv * dup.seed * (optionally data.encrypted just to test decryption)
Start an auth,policy session
tpm2_startauthsession --policy-session -S session.dat
tpm2_policycommandcode -S session.dat -L dpolicy.dat TPM2_CC_Duplicate
Load the context we used to transfer
tpm2_flushcontext --transient-object
tpm2_load -C primary.ctx -u new_parent.pub -r new_parent.prv -c new_parent.ctx
Import the duplicated context against the parent we used
tpm2_import -C new_parent.ctx -u dup.pub -i dup.dpriv \
-r dup.prv -s dup.seed -L dpolicy.dat
Load the duplicated key context
tpm2_flushcontext --transient-object
tpm2_load -C new_parent.ctx -u dup.pub -r dup.prv -c dup.ctx
Test the imported key matches
echo "meet me at.." >file.txt
tpm2_sign -c dup.ctx -g sha256 -o sig.rss -p foo file.txt
dd if=sig.rss of=sign.raw bs=1 skip=6 count=256
Compare the signature file hash:
$ sha256sum sign.raw
a1b4e3fbaa29e6e46d95cff498150b6b8e7d9fd21182622e8f5a3ddde257879e
tpm2_flushcontext --transient-object
tpm2_rsadecrypt -p foo -c dup.ctx -o data.ptext data.encrypted
# cat data.ptext
meet me at..
Tools can return any of the following codes:
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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