References¶

Passwords¶

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.

String¶

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

Examples¶

foobar
str:foobar
    

Hex-string¶

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.

Example¶

hex:0x1122334455667788
    

File¶

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.

Examples¶

# 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
    

Sessions¶

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.

Examples¶

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
    

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

PCR bank specifiers (pcr.md)

Examples¶

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.

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¶

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rsa

•

ecc

Symmetric¶

•

aes

•

camellia

Hashing Algorithms¶

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sha1

•

sha256

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sha384

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sha512

•

sm3_256

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sha3_256

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sha3_384

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sha3_512

Keyed Hash¶

•

hmac

•

xor

Signing Schemes¶

•

rsassa

•

rsapss

•

ecdsa

•

ecdaa

•

ecschnorr

Asymmetric Encryption Schemes¶

•

oaep

•

rsaes

•

ecdh

Modes¶

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ctr

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ofb

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cbc

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cfb

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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

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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

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ecdh

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rsassa

•

rsapss

•

ecdsa

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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.

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.

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.

On 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.

On 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)

On TPM-B¶

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

•

Sign

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
    

•

Decryption

tpm2_flushcontext --transient-object
tpm2_rsadecrypt -p foo -c dup.ctx -o data.ptext data.encrypted
# cat data.ptext 
meet me at..
    

Exporting an OpenSSL RSA key for a remote TPM¶

To securely send an OpenSSL generated RSA key to a remote TPM such that only that remote TPM will be able to load it, and without exposing the private key to the host operating system on the remote machine:

•

On the destination TPM-B, create a primary context and read its public key, then send primary.pub to the source machine:

tpm2_createprimary -c primary.ctx
tpm2_readpublic -c primary.ctx -o primary.pub
    

•

On the source machine create the RSA private key and wrap it for the destination TPM’s public key. Similar to tpm2_makecredential, this step should not require a TPM.

openssl genrsa -out rsa.pem
tpm2_duplicate -U primary.pub -G rsa -k rsa.pem -u rsa.pub -r rsa.dpriv -s rsa.seed
    

•

Send the rsa.pub, rsa.dpriv and rsa.seed to the destination TPM-B and import the files, which will decrypt them using the primary.ctx to produce rsa.priv, which can then be loaded and used as a TPM key:

tpm2_import -C primary.ctx -G rsa -i rsa.dpriv -s rsa.seed -u rsa.pub -r rsa.priv
tpm2_load -C primary.ctx -c rsa.ctx -u rsa.pub -r rsa.priv