class MAC(object):
"""Class describing the MAC algorithm to use and how to get the key.
Instances of this class provide the following attributes:
algorithm: the name of the HMAC to use (currently only HMAC_SHA1)
key: the binary value of the MAC key if it can be decrypted
"""
def __init__(self, pskc, mac_method=None):
from pskc.encryption import EncryptedValue
self.algorithm = None
self._mac_key = EncryptedValue(pskc.encryption)
self.parse(mac_method)
def parse(self, mac_method):
"""Read MAC information from the <MACMethod> XML tree."""
from pskc.xml import find, findtext
if mac_method is None:
return
self.algorithm = mac_method.get('Algorithm')
self._mac_key.parse(find(mac_method, 'pskc:MACKey'))
mac_key_reference = findtext(mac_method, 'pskc:MACKeyReference')
@property
def key(self):
"""Provides access to the MAC key binary value if available."""
return self._mac_key.decrypt()
def __init__(self, key, element=None):
self.value = None
self.encrypted_value = EncryptedValue(key.pskc.encryption)
self.value_mac = ValueMAC(key.pskc.mac)
self.parse(element)
class DataType(object):
"""Provide access to possibly encrypted, MAC'ed information.
This class is meant to be subclassed to provide typed access to stored
values. Instances of this class provide the following attributes:
value: unencrypted value if present
encrypted_value: reference to an EncryptedValue instance
value_mac: reference to a ValueMAC instance
"""
def __init__(self, key, element=None):
self.value = None
self.encrypted_value = EncryptedValue(key.pskc.encryption)
self.value_mac = ValueMAC(key.pskc.mac)
self.parse(element)
def parse(self, element):
"""Read information from the provided element.
The element is expected to contain <PlainValue>, <EncryptedValue>
and/or ValueMAC elements that contain information on the actual
value."""
from pskc.xml import find, findtext
if element is None:
return
value = findtext(element, "pskc:PlainValue")
if value is not None:
self.value = self.from_text(value)
self.encrypted_value.parse(find(element, "pskc:EncryptedValue"))
self.value_mac.parse(find(element, "pskc:ValueMAC"))
def make_xml(self, key, tag):
from pskc.xml import find, mk_elem
# skip empty values
value = self.get_value()
if value is None:
return
# find the data tag and create our tag under it
data = find(key, "pskc:Data")
if data is None:
data = mk_elem(key, "pskc:Data", empty=True)
element = mk_elem(data, tag, empty=True)
mk_elem(element, "pskc:PlainValue", self.to_text(self.value))
def get_value(self):
"""Provide the raw binary value."""
if self.value is not None:
return self.value
if self.encrypted_value.cipher_value:
# check MAC and decrypt
self.check()
return self.from_bin(self.encrypted_value.decrypt())
def set_value(self, value):
"""Set the unencrypted value."""
self.value = value
self.encrypted_value.cipher_value = None
def check(self):
"""Check whether the embedded MAC is correct."""
# this checks the encrypted value
return self.value_mac.check(self.encrypted_value.cipher_value)
def __init__(self, pskc, mac_method=None):
from pskc.encryption import EncryptedValue
self.algorithm = None
self._mac_key = EncryptedValue(pskc.encryption)
self.parse(mac_method)
