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tpm.py
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tpm.py
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# Copyright (C) 2024 VyOS maintainers and contributors
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License version 2 or later as
# published by the Free Software Foundation.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
import os
import tempfile
from vyos.utils.process import rc_cmd
default_pcrs = ['0','2','4','7']
tpm_handle = 0x81000000
def init_tpm(clear=False):
"""
Initialize TPM
"""
code, output = rc_cmd('tpm2_startup' + (' -c' if clear else ''))
if code != 0:
raise Exception('init_tpm: Failed to initialize TPM')
def clear_tpm_key():
"""
Clear existing key on TPM
"""
code, output = rc_cmd(f'tpm2_evictcontrol -C o -c {tpm_handle}')
if code != 0:
raise Exception('clear_tpm_key: Failed to clear TPM key')
def read_tpm_key(index=0, pcrs=default_pcrs):
"""
Read existing key on TPM
"""
with tempfile.TemporaryDirectory() as tpm_dir:
pcr_str = ",".join(pcrs)
tpm_key_file = os.path.join(tpm_dir, 'tpm_key.key')
code, output = rc_cmd(f'tpm2_unseal -c {tpm_handle + index} -p pcr:sha256:{pcr_str} -o {tpm_key_file}')
if code != 0:
raise Exception('read_tpm_key: Failed to read key from TPM')
with open(tpm_key_file, 'rb') as f:
tpm_key = f.read()
return tpm_key
def write_tpm_key(key, index=0, pcrs=default_pcrs):
"""
Saves key to TPM
"""
with tempfile.TemporaryDirectory() as tpm_dir:
pcr_str = ",".join(pcrs)
policy_file = os.path.join(tpm_dir, 'policy.digest')
code, output = rc_cmd(f'tpm2_createpolicy --policy-pcr -l sha256:{pcr_str} -L {policy_file}')
if code != 0:
raise Exception('write_tpm_key: Failed to create policy digest')
primary_context_file = os.path.join(tpm_dir, 'primary.ctx')
code, output = rc_cmd(f'tpm2_createprimary -C e -g sha256 -G rsa -c {primary_context_file}')
if code != 0:
raise Exception('write_tpm_key: Failed to create primary key')
key_file = os.path.join(tpm_dir, 'crypt.key')
with open(key_file, 'wb') as f:
f.write(key)
public_obj = os.path.join(tpm_dir, 'obj.pub')
private_obj = os.path.join(tpm_dir, 'obj.key')
code, output = rc_cmd(
f'tpm2_create -g sha256 \
-u {public_obj} -r {private_obj} \
-C {primary_context_file} -L {policy_file} -i {key_file}')
if code != 0:
raise Exception('write_tpm_key: Failed to create object')
load_context_file = os.path.join(tpm_dir, 'load.ctx')
code, output = rc_cmd(f'tpm2_load -C {primary_context_file} -u {public_obj} -r {private_obj} -c {load_context_file}')
if code != 0:
raise Exception('write_tpm_key: Failed to load object')
code, output = rc_cmd(f'tpm2_evictcontrol -c {load_context_file} -C o {tpm_handle + index}')
if code != 0:
raise Exception('write_tpm_key: Failed to write object to TPM')

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