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# key.py - module for handling keys from pskc files
# coding: utf-8
#
# Copyright (C) 2014-2022 Arthur de Jong
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# This library 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
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
# 02110-1301 USA
"""Module that handles keys stored in PSKC files."""
import array
import binascii
from pskc.policy import Policy
class EncryptedValue(object):
"""A container for an encrypted value."""
def __init__(self, cipher_value, mac_value, algorithm):
self.cipher_value = cipher_value
self.mac_value = mac_value
self.algorithm = algorithm
@classmethod
def create(cls, pskc, value):
"""Construct an encryped value from a plaintext value."""
# force conversion to bytestring on Python 3
if not isinstance(value, (type(b''), bytearray)):
value = value.encode() # pragma: no cover (Python 3 specific)
cipher_value = pskc.encryption.encrypt_value(value)
mac_value = None
if pskc.mac.algorithm:
mac_value = pskc.mac.generate_mac(cipher_value)
return cls(cipher_value, mac_value, pskc.encryption.algorithm)
def get_value(self, pskc):
"""Provide the decrypted value."""
from pskc.exceptions import DecryptionError
plaintext = pskc.encryption.decrypt_value(
self.cipher_value, self.algorithm)
# allow MAC over plaintext or ciphertext
# (RFC 6030 implies MAC over ciphertext but older draft used
# MAC over plaintext)
if self.mac_value and self.mac_value not in (
pskc.mac.generate_mac(self.cipher_value),
pskc.mac.generate_mac(plaintext)):
raise DecryptionError('MAC value does not match')
return plaintext
class EncryptedIntegerValue(EncryptedValue):
"""Class representing an encrypted integer value."""
@classmethod
def create(cls, pskc, value):
"""Construct an encryped value from a plaintext value."""
value = '%x' % value
n = len(value)
value = binascii.unhexlify(value.zfill(n + (n & 1)))
return super(EncryptedIntegerValue, cls).create(pskc, value)
def get_value(self, pskc):
"""Provide the decrypted integer value."""
value = super(EncryptedIntegerValue, self).get_value(pskc)
# try to handle value as ASCII representation
if value.isdigit():
return int(value)
# fall back to do big-endian decoding
result = 0
for x in array.array('B', value):
result = (result << 8) + x
return result
class DataTypeProperty(object):
"""A data descriptor that delegates actions to DataType instances."""
def __init__(self, name, doc):
self.name = name
self.__doc__ = doc
def __get__(self, obj, objtype):
value = getattr(obj, '_' + self.name, None)
if hasattr(value, 'get_value'):
return value.get_value(obj.device.pskc)
else:
return value
def __set__(self, obj, val):
setattr(obj, '_' + self.name, val)
class DeviceProperty(object):
"""A data descriptor that delegates actions to the Device instance."""
def __init__(self, name):
self.name = name
def __get__(self, obj, objtype):
return getattr(obj.device, self.name)
def __set__(self, obj, val):
setattr(obj.device, self.name, val)
class Key(object):
"""Representation of a single key from a PSKC file.
Instances of this class provide the following properties:
id: unique key identifier (should be constant between interchanges)
algorithm: identifier of the PSKC algorithm profile (URI)
secret: the secret key itself (binary form, automatically decrypted)
counter: event counter for event-based OTP
time_offset: time offset for time-based OTP algorithms (in intervals)
time_interval: time interval for time-based OTP in seconds
time_drift: device clock drift (negative means device is slow)
issuer: party that issued the key
key_profile: reference to pre-shared key profile information
key_reference: reference to an external key
friendly_name: human-readable name for the secret key
key_userid: user distinguished name associated with the key
algorithm_suite: additional algorithm characteristics (e.g. used hash)
challenge_encoding: format of the challenge for CR devices
challenge_min_length: minimum accepted challenge length by device
challenge_max_length: maximum size challenge accepted by the device
challenge_check: whether the device will check an embedded check digit
response_encoding: format of the response the device will generate
response_length: the length of the response of the device
response_check: whether the device appends a Luhn check digit
policy: reference to policy information (see Policy class)
This class also provides access to the manufacturer, serial, model,
issue_no, device_binding, start_date, expiry_date, device_userid and
crypto_module properties of the Device class.
"""
def __init__(self, device):
self.device = device
self.id = None
self.algorithm = None
self.issuer = None
self.key_profile = None
self.key_reference = None
self.friendly_name = None
self.key_userid = None
self.algorithm_suite = None
self.challenge_encoding = None
self.challenge_min_length = None
self.challenge_max_length = None
self.challenge_check = None
self.response_encoding = None
self.response_length = None
self.response_check = None
self.policy = Policy(self)
secret = DataTypeProperty(
'secret', 'The secret key itself.')
counter = DataTypeProperty(
'counter', 'An event counter for event-based OTP.')
time_offset = DataTypeProperty(
'time_offset',
'A time offset for time-based OTP (number of intervals).')
time_interval = DataTypeProperty(
'time_interval', 'A time interval in seconds.')
time_drift = DataTypeProperty(
'time_drift', 'Device clock drift value (number of time intervals).')
manufacturer = DeviceProperty('manufacturer')
serial = DeviceProperty('serial')
model = DeviceProperty('model')
issue_no = DeviceProperty('issue_no')
device_binding = DeviceProperty('device_binding')
start_date = DeviceProperty('start_date')
expiry_date = DeviceProperty('expiry_date')
device_userid = DeviceProperty('device_userid')
crypto_module = DeviceProperty('crypto_module')
def check(self):
"""Check if all MACs in the message are valid."""
if all(x is not False for x in (
self.secret, self.counter, self.time_offset,
self.time_interval, self.time_drift)):
return True
@property
def userid(self):
"""User identifier (either the key or device userid)."""
return self.key_userid or self.device_userid
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