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sec_contexts.py
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import six from gssapi.raw import sec_contexts as rsec_contexts from gssapi.raw import message as rmessage from gssapi.raw import named_tuples as tuples from gssapi.raw.types import RequirementFlag, IntEnumFlagSet import gssapi.exceptions as excs from gssapi import _utils from gssapi.names import Name from gssapi.creds import Credentials @six.add_metaclass(_utils.CheckLastError) class SecurityContext(rsec_contexts.SecurityContext): """A GSSAPI Security Context This class represents a GSSAPI security context that may be used with and/or returned by other GSSAPI methods. It inherits from the low-level GSSAPI :class:`~gssapi.raw.sec_contexts.SecurityContext` class, and thus may used with both low-level and high-level API methods. This class may be pickled and unpickled (the attached delegated credentials object will not be preserved, however). """ def __new__(cls, base=None, token=None, name=None, creds=None, lifetime=None, flags=None, mech=None, channel_bindings=None, usage=None): if token is not None: base = rsec_contexts.import_sec_context(token) return super(SecurityContext, cls).__new__(cls, base) def __init__(self, base=None, token=None, name=None, creds=None, lifetime=None, flags=None, mech=None, channel_bindings=None, usage=None): """ The constructor creates a new security context, but does not begin the initiate or accept process. If the `base` argument is used, an existing :class:`~gssapi.raw.sec_contexts.SecurityContext` object from the low-level API is converted into a high-level object. If the `token` argument is passed, the security context is imported using the token. Otherwise, a new security context is created. If the `usage` argument is not passed, the constructor will attempt to detect what the appropriate usage is based on either the existing security context (if `base` or `token` are used) or the argument set. For a security context of the `initiate` usage, the `name` argument must be used, and the `creds`, `mech`, `flags`, `lifetime`, and `channel_bindings` arguments may be used as well. For a security context of the `accept` usage, the `creds` and `channel_bindings` arguments may optionally be used. """ # NB(directxman12): _last_err must be set first self._last_err = None # determine the usage ('initiate' vs 'accept') if base is None and token is None: # this will be a new context if usage is not None: if usage not in ('initiate', 'accept'): msg = "Usage must be either 'initiate' or 'accept'" raise excs.UnknownUsageError(msg, obj="security context") self.usage = usage elif creds is not None and creds.usage != 'both': self.usage = creds.usage elif name is not None: # if we pass a name, assume the usage is 'initiate' self.usage = 'initiate' else: # if we don't pass a name, assume the usage is 'accept' self.usage = 'accept' # check for appropriate arguments if self.usage == 'initiate': # takes: creds?, target_name, mech?, flags?, # channel_bindings? if name is None: raise TypeError("You must pass the 'name' argument when " "creating an initiating security context") self._target_name = name self._mech = mech self._desired_flags = IntEnumFlagSet(RequirementFlag, flags) self._desired_lifetime = lifetime else: # takes creds? if (name is not None or flags is not None or mech is not None or lifetime is not None): raise TypeError("You must pass at most the 'creds' " "argument when creating an accepting " "security context") self._channel_bindings = channel_bindings self._creds = creds self._delegated_creds = None else: # we already have a context in progress, just inspect it # NB(directxman12): MIT krb5 refuses to inquire about a context # if it's partially established, so we have to check here try: if self.locally_initiated: self.usage = 'initiate' else: self.usage = 'accept' except excs.MissingContextError: msg = ("Cannot extract usage from a partially completed " "context") raise excs.UnknownUsageError(msg, obj="security context") # This is to work around an MIT krb5 bug (see the `complete` property) self._complete = None # NB(directxman12): DO NOT ADD AN __del__ TO THIS CLASS -- it screws up # the garbage collector if _last_tb is still defined # TODO(directxman12): implement flag properties def get_signature(self, message): """Calculate the signature for a message. This method calculates the signature (called a MIC) for the given message, which may be then used with :meth:`verify_signature` to confirm the validity of the signature. This is useful if you wish to transmit the message signature and message in your own format. Args: message (bytes): the input message Returns: bytes: the message signature Raises: ExpiredContextError MissingContextError BadQoPError """ # TODO(directxman12): check flags? return rmessage.get_mic(self, message) def verify_signature(self, message, mic): """Verify the signature for a message. This method verifies that a signature (generated by :meth:`get_signature` is valid for the given message. If the signature is valid, the method will return. Otherwise, it will raise an error. Args: message (bytes): the message mic (bytes): the signature to verify Raises: BadMICError: the signature was not valid InvalidTokenError DuplicateTokenError ExpiredTokenError TokenTooLateError TokenTooEarlyError ExpiredContextError MissingContextError """ return rmessage.verify_mic(self, message, mic) def wrap(self, message, encrypt): """Wrap a message, optionally with encryption This wraps a message, signing it and optionally encrypting it. Args: message (bytes): the message to wrap encrypt (bool): whether or not to encrypt the message Returns: WrapResult: the wrapped message and details about it (e.g. whether encryption was used succesfully) Raises: ExpiredContextError MissingContextError BadQoPError """ return rmessage.wrap(self, message, encrypt) def unwrap(self, message): """Unwrap a wrapped message. This method unwraps/unencrypts a wrapped message, verifying the signature along the way. Args: message (bytes): the message to unwrap/decrypt Returns: UnwrapResult: the unwrapped message and details about it (e.g. wheter encryption was used) Raises: InvalidTokenError BadMICError DuplicateTokenError ExpiredTokenError TokenTooLateError TokenTooEarlyError ExpiredContextError MissingContextError """ return rmessage.unwrap(self, message) def encrypt(self, message): """Encrypt a message. This method wraps and encrypts a message, similarly to :meth:`wrap`. The difference is that encryption is always used, and the method will raise an exception if this is not possible. Additionally, this method simply returns the encrypted message directly. Args: message (bytes): the message to encrypt Returns: bytes: the encrypted message Raises: EncryptionNotUsed: the encryption could not be used ExpiredContextError MissingContextError BadQoPError """ res = self.wrap(message, encrypt=True) if not res.encrypted: raise excs.EncryptionNotUsed("Wrapped message was not encrypted") return res.message def decrypt(self, message): """Decrypt a message. This method decrypts and unwraps a message, verifying the signature along the way, similarly to :meth:`unwrap`. The difference is that this method will raise an exception if encryption was established by the context and not used, and simply returns the decrypted message directly. Args: message (bytes): the encrypted message Returns: bytes: the decrypted message Raises: EncryptionNotUsed: encryption was expected, but not used InvalidTokenError BadMICError DuplicateTokenError ExpiredTokenError TokenTooLateError TokenTooEarlyError ExpiredContextError MissingContextError """ res = self.unwrap(message) if (not res.encrypted and self.actual_flags & RequirementFlag.confidentiality): raise excs.EncryptionNotUsed("The context was established with " "encryption, but unwrapped message " "was not encrypted", unwrapped_message=res.message) return res.message def get_wrap_size_limit(self, desired_output_size, encrypted=True): """Calculate the maximum message size for a given wrapped message size. This method calculates the maximum input message size for a given maximum wrapped/encrypted message size. Args: desired_output_size (int): the maximum output message size encrypted (bool): whether or not encryption should be taken into account Returns: int: the maximum input message size Raises: MissingContextError ExpiredContextError BadQoPError """ return rmessage.wrap_size_limit(self, desired_output_size, encrypted) def process_token(self, token): """Process an output token asynchronously. This method processes an output token even when the security context was not expecting it. Warning: This method is deprecated. Args: token (bytes): the token to process Raises: InvalidTokenError MissingContextError """ rsec_contexts.process_context_token(self, token) def export(self): """Export a security context. This method exports a security context, allowing it to be passed between processes. Returns: bytes: the exported security context Raises: ExpiredContextError MissingContextError OperationUnavailableError """ return rsec_contexts.export_sec_context(self) _INQUIRE_ARGS = ('initiator_name', 'target_name', 'lifetime', 'mech', 'flags', 'locally_init', 'complete') @_utils.check_last_err def _inquire(self, **kwargs): """Inspect the security context for information This method inspects the security context for information. If no keyword arguments are passed, all available information is returned. Otherwise, only the keyword arguments that are passed and set to `True` are returned. Args: initiator_name (bool): get the initiator name for this context target_name (bool): get the target name for this context lifetime (bool): get the remaining lifetime for this context mech (bool): get the :class:`MechType` used by this context flags (bool): get the flags set on this context locally_init (bool): get whether this context was locally initiated complete (bool): get whether negotiation on this context has been completed Returns: InquireContextResult: the results of the inquiry, with unused fields set to None Raises: MissingContextError """ if not kwargs: default_val = True else: default_val = False for arg in self._INQUIRE_ARGS: kwargs[arg] = kwargs.get(arg, default_val) res = rsec_contexts.inquire_context(self, **kwargs) if (kwargs.get('initiator_name', False) and res.initiator_name is not None): init_name = Name(res.initiator_name) else: init_name = None if (kwargs.get('target_name', False) and res.target_name is not None): target_name = Name(res.target_name) else: target_name = None return tuples.InquireContextResult(init_name, target_name, res.lifetime, res.mech, res.flags, res.locally_init, res.complete) @property def lifetime(self): """The amount of time for which this context remains valid""" return rsec_contexts.context_time(self) @property def delegated_creds(self): """The credentials delegated from the initiator to the acceptor .. warning:: This value will not be preserved across picklings. These should be separately exported and transfered. """ return self._delegated_creds initiator_name = _utils.inquire_property( 'initiator_name', 'The :class:`Name` of the initiator of this context') target_name = _utils.inquire_property( 'target_name', 'The :class:`Name` of the target of this context') mech = _utils.inquire_property( 'mech', 'The mechanism (:class:`MechType`) in use by this context') actual_flags = _utils.inquire_property( 'flags', 'The flags set on this context') locally_initiated = _utils.inquire_property( 'locally_init', 'Whether this context was locally intiated') @property @_utils.check_last_err def complete(self): """Whether negotiation for this context has been completed""" # NB(directxman12): MIT krb5 has a bug where it refuses to # inquire about partially completed contexts, # so we can't just use `self._inquire` generally if self._started: if self._complete is None: try: res = self._inquire(complete=True).complete except excs.MissingContextError: return False else: self._complete = res return self._complete else: return False @_utils.catch_and_return_token def step(self, token=None): """Perform a negotation step. This method performs a negotiation step based on the usage type of this context. If `__DEFER_STEP_ERRORS__` is set to True on the class, this method will return a token, even when exceptions would be thrown. The generated exception will be thrown on the next method call or property lookup on the context. **This is the default behavior.** This method should be used in a while loop, as such: .. code-block:: python input_token = None try: while not ctx.complete: output_token = ctx.step(input_token) input_token = send_and_receive(output_token) except GSSError as e: handle_the_issue() .. tip:: Disabling `__DEFER_STEP_ERRORS__` is rarely necessary. When this method is used in a loop (as above), `__DEFER_STEP_ERRORS__` will ensure that you always send an error token when it's available, keeping the other end of the security context updated with the status of the negotiation. Args: token (bytes): the input token from the other participant's step Returns: bytes: the output token to send to the other participant Raises: InvalidTokenError InvalidCredentialsError MissingCredentialsError ExpiredCredentialsError BadChannelBindingsError BadMICError ExpiredTokenError: (initiate only) DuplicateTokenError MissingContextError BadNameTypeError: (initiate only) BadNameError: (initiate only) BadMechanismError """ if self.usage == 'accept': return self._acceptor_step(token=token) else: return self._initiator_step(token=token) def _acceptor_step(self, token): res = rsec_contexts.accept_sec_context(token, self._creds, self, self._channel_bindings) if res.delegated_creds is not None: self._delegated_creds = Credentials(res.delegated_creds) else: self._delegated_creds = None self._complete = not res.more_steps return res.token def _initiator_step(self, token=None): res = rsec_contexts.init_sec_context(self._target_name, self._creds, self, self._mech, self._desired_flags, self._desired_lifetime, self._channel_bindings, token) self._complete = not res.more_steps return res.token # pickle protocol support def __reduce__(self): # the unpickle arguments to new are (base=None, token=self.export()) return (type(self), (None, self.export()))