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+# -*- coding: utf-8 -*-
+# gateway.py
+# Copyright (C) 2013 LEAP
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# 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/>.
+
+"""
+LEAP SMTP encrypted gateway.
+
+The following classes comprise the SMTP gateway service:
+
+ * SMTPFactory - A twisted.internet.protocol.ServerFactory that provides
+ the SMTPDelivery protocol.
+ * SMTPDelivery - A twisted.mail.smtp.IMessageDelivery implementation. It
+ knows how to validate sender and receiver of messages and it generates
+ an EncryptedMessage for each recipient.
+ * SSLContextFactory - Contains the relevant ssl information for the
+ connection.
+ * EncryptedMessage - An implementation of twisted.mail.smtp.IMessage that
+ knows how to encrypt/sign itself before sending.
+
+
+"""
+
+import re
+from StringIO import StringIO
+from email.Header import Header
+from email.utils import parseaddr
+from email.parser import Parser
+from email.mime.application import MIMEApplication
+
+from zope.interface import implements
+from OpenSSL import SSL
+from twisted.mail import smtp
+from twisted.internet.protocol import ServerFactory
+from twisted.internet import reactor, ssl
+from twisted.internet import defer
+from twisted.python import log
+
+from leap.common.check import leap_assert, leap_assert_type
+from leap.common.events import proto, signal
+from leap.keymanager import KeyManager
+from leap.keymanager.openpgp import OpenPGPKey
+from leap.keymanager.errors import KeyNotFound
+from leap.mail.smtp.rfc3156 import (
+ MultipartSigned,
+ MultipartEncrypted,
+ PGPEncrypted,
+ PGPSignature,
+ RFC3156CompliantGenerator,
+ encode_base64_rec,
+)
+
+# replace email generator with a RFC 3156 compliant one.
+from email import generator
+generator.Generator = RFC3156CompliantGenerator
+
+
+#
+# Helper utilities
+#
+
+def validate_address(address):
+ """
+ Validate C{address} as defined in RFC 2822.
+
+ :param address: The address to be validated.
+ :type address: str
+
+ @return: A valid address.
+ @rtype: str
+
+ @raise smtp.SMTPBadRcpt: Raised if C{address} is invalid.
+ """
+ leap_assert_type(address, str)
+ # in the following, the address is parsed as described in RFC 2822 and
+ # ('', '') is returned if the parse fails.
+ _, address = parseaddr(address)
+ if address == '':
+ raise smtp.SMTPBadRcpt(address)
+ return address
+
+
+#
+# SMTPFactory
+#
+
+class SMTPFactory(ServerFactory):
+ """
+ Factory for an SMTP server with encrypted gatewaying capabilities.
+ """
+
+ def __init__(self, userid, keymanager, host, port, cert, key,
+ encrypted_only):
+ """
+ Initialize the SMTP factory.
+
+ :param userid: The user currently logged in
+ :type userid: unicode
+ :param keymanager: A KeyManager for retrieving recipient's keys.
+ :type keymanager: leap.common.keymanager.KeyManager
+ :param host: The hostname of the remote SMTP server.
+ :type host: str
+ :param port: The port of the remote SMTP server.
+ :type port: int
+ :param cert: The client certificate for authentication.
+ :type cert: str
+ :param key: The client key for authentication.
+ :type key: str
+ :param encrypted_only: Whether the SMTP gateway should send unencrypted
+ mail or not.
+ :type encrypted_only: bool
+ """
+ # assert params
+ leap_assert_type(keymanager, KeyManager)
+ leap_assert_type(host, str)
+ leap_assert(host != '')
+ leap_assert_type(port, int)
+ leap_assert(port is not 0)
+ leap_assert_type(cert, unicode)
+ leap_assert(cert != '')
+ leap_assert_type(key, unicode)
+ leap_assert(key != '')
+ leap_assert_type(encrypted_only, bool)
+ # and store them
+ self._userid = userid
+ self._km = keymanager
+ self._host = host
+ self._port = port
+ self._cert = cert
+ self._key = key
+ self._encrypted_only = encrypted_only
+
+ def buildProtocol(self, addr):
+ """
+ Return a protocol suitable for the job.
+
+ :param addr: An address, e.g. a TCP (host, port).
+ :type addr: twisted.internet.interfaces.IAddress
+
+ @return: The protocol.
+ @rtype: SMTPDelivery
+ """
+ smtpProtocol = smtp.SMTP(SMTPDelivery(
+ self._userid, self._km, self._host, self._port, self._cert,
+ self._key, self._encrypted_only))
+ smtpProtocol.factory = self
+ return smtpProtocol
+
+
+#
+# SMTPDelivery
+#
+
+class SMTPDelivery(object):
+ """
+ Validate email addresses and handle message delivery.
+ """
+
+ implements(smtp.IMessageDelivery)
+
+ def __init__(self, userid, keymanager, host, port, cert, key,
+ encrypted_only):
+ """
+ Initialize the SMTP delivery object.
+
+ :param userid: The user currently logged in
+ :type userid: unicode
+ :param keymanager: A KeyManager for retrieving recipient's keys.
+ :type keymanager: leap.common.keymanager.KeyManager
+ :param host: The hostname of the remote SMTP server.
+ :type host: str
+ :param port: The port of the remote SMTP server.
+ :type port: int
+ :param cert: The client certificate for authentication.
+ :type cert: str
+ :param key: The client key for authentication.
+ :type key: str
+ :param encrypted_only: Whether the SMTP gateway should send unencrypted
+ mail or not.
+ :type encrypted_only: bool
+ """
+ self._userid = userid
+ self._km = keymanager
+ self._userid = userid
+ self._km = keymanager
+ self._host = host
+ self._port = port
+ self._cert = cert
+ self._key = key
+ self._encrypted_only = encrypted_only
+ self._origin = None
+
+ def receivedHeader(self, helo, origin, recipients):
+ """
+ Generate the 'Received:' header for a message.
+
+ :param helo: The argument to the HELO command and the client's IP
+ address.
+ :type helo: (str, str)
+ :param origin: The address the message is from.
+ :type origin: twisted.mail.smtp.Address
+ :param recipients: A list of the addresses for which this message is
+ bound.
+ :type: list of twisted.mail.smtp.User
+
+ @return: The full "Received" header string.
+ :type: str
+ """
+ myHostname, clientIP = helo
+ headerValue = "by %s from %s with ESMTP ; %s" % (
+ myHostname, clientIP, smtp.rfc822date())
+ # email.Header.Header used for automatic wrapping of long lines
+ return "Received: %s" % Header(headerValue)
+
+ def validateTo(self, user):
+ """
+ Validate the address of C{user}, a recipient of the message.
+
+ This method is called once for each recipient and validates the
+ C{user}'s address against the RFC 2822 definition. If the
+ configuration option ENCRYPTED_ONLY_KEY is True, it also asserts the
+ existence of the user's key.
+
+ In the end, it returns an encrypted message object that is able to
+ send itself to the C{user}'s address.
+
+ :param user: The user whose address we wish to validate.
+ :type: twisted.mail.smtp.User
+
+ @return: A Deferred which becomes, or a callable which takes no
+ arguments and returns an object implementing IMessage. This will
+ be called and the returned object used to deliver the message when
+ it arrives.
+ @rtype: no-argument callable
+
+ @raise SMTPBadRcpt: Raised if messages to the address are not to be
+ accepted.
+ """
+ # try to find recipient's public key
+ try:
+ address = validate_address(user.dest.addrstr)
+ # verify if recipient key is available in keyring
+ self._km.get_key(address, OpenPGPKey) # might raise KeyNotFound
+ log.msg("Accepting mail for %s..." % user.dest.addrstr)
+ signal(proto.SMTP_RECIPIENT_ACCEPTED_ENCRYPTED, user.dest.addrstr)
+ except KeyNotFound:
+ # if key was not found, check config to see if will send anyway.
+ if self._encrypted_only:
+ signal(proto.SMTP_RECIPIENT_REJECTED, user.dest.addrstr)
+ raise smtp.SMTPBadRcpt(user.dest.addrstr)
+ log.msg("Warning: will send an unencrypted message (because "
+ "encrypted_only' is set to False).")
+ signal(
+ proto.SMTP_RECIPIENT_ACCEPTED_UNENCRYPTED, user.dest.addrstr)
+ return lambda: EncryptedMessage(
+ self._origin, user, self._km, self._host, self._port, self._cert,
+ self._key)
+
+ def validateFrom(self, helo, origin):
+ """
+ Validate the address from which the message originates.
+
+ :param helo: The argument to the HELO command and the client's IP
+ address.
+ :type: (str, str)
+ :param origin: The address the message is from.
+ :type origin: twisted.mail.smtp.Address
+
+ @return: origin or a Deferred whose callback will be passed origin.
+ @rtype: Deferred or Address
+
+ @raise twisted.mail.smtp.SMTPBadSender: Raised if messages from this
+ address are not to be accepted.
+ """
+ # accept mail from anywhere. To reject an address, raise
+ # smtp.SMTPBadSender here.
+ if str(origin) != str(self._userid):
+ log.msg("Rejecting sender {0}, expected {1}".format(origin,
+ self._userid))
+ raise smtp.SMTPBadSender(origin)
+ self._origin = origin
+ return origin
+
+
+#
+# EncryptedMessage
+#
+
+class SSLContextFactory(ssl.ClientContextFactory):
+ def __init__(self, cert, key):
+ self.cert = cert
+ self.key = key
+
+ def getContext(self):
+ self.method = SSL.TLSv1_METHOD # SSLv23_METHOD
+ ctx = ssl.ClientContextFactory.getContext(self)
+ ctx.use_certificate_file(self.cert)
+ ctx.use_privatekey_file(self.key)
+ return ctx
+
+
+def move_headers(origmsg, newmsg):
+ headers = origmsg.items()
+ unwanted_headers = ['content-type', 'mime-version', 'content-disposition',
+ 'content-transfer-encoding']
+ headers = filter(lambda x: x[0].lower() not in unwanted_headers, headers)
+ for hkey, hval in headers:
+ newmsg.add_header(hkey, hval)
+ del(origmsg[hkey])
+
+
+class EncryptedMessage(object):
+ """
+ Receive plaintext from client, encrypt it and send message to a
+ recipient.
+ """
+ implements(smtp.IMessage)
+
+ def __init__(self, fromAddress, user, keymanager, host, port, cert, key):
+ """
+ Initialize the encrypted message.
+
+ :param fromAddress: The address of the sender.
+ :type fromAddress: twisted.mail.smtp.Address
+ :param user: The recipient of this message.
+ :type user: twisted.mail.smtp.User
+ :param keymanager: A KeyManager for retrieving recipient's keys.
+ :type keymanager: leap.common.keymanager.KeyManager
+ :param host: The hostname of the remote SMTP server.
+ :type host: str
+ :param port: The port of the remote SMTP server.
+ :type port: int
+ :param cert: The client certificate for authentication.
+ :type cert: str
+ :param key: The client key for authentication.
+ :type key: str
+ """
+ # assert params
+ leap_assert_type(user, smtp.User)
+ leap_assert_type(keymanager, KeyManager)
+ # and store them
+ self._fromAddress = fromAddress
+ self._user = user
+ self._km = keymanager
+ self._host = host
+ self._port = port
+ self._cert = cert
+ self._key = key
+ # initialize list for message's lines
+ self.lines = []
+
+ #
+ # methods from smtp.IMessage
+ #
+
+ def lineReceived(self, line):
+ """
+ Handle another line.
+
+ :param line: The received line.
+ :type line: str
+ """
+ self.lines.append(line)
+
+ def eomReceived(self):
+ """
+ Handle end of message.
+
+ This method will encrypt and send the message.
+ """
+ log.msg("Message data complete.")
+ self.lines.append('') # add a trailing newline
+ try:
+ self._maybe_encrypt_and_sign()
+ return self.sendMessage()
+ except KeyNotFound:
+ return None
+
+ def parseMessage(self):
+ """
+ Separate message headers from body.
+ """
+ parser = Parser()
+ return parser.parsestr('\r\n'.join(self.lines))
+
+ def connectionLost(self):
+ """
+ Log an error when the connection is lost.
+ """
+ log.msg("Connection lost unexpectedly!")
+ log.err()
+ signal(proto.SMTP_CONNECTION_LOST, self._user.dest.addrstr)
+ # unexpected loss of connection; don't save
+ self.lines = []
+
+ def sendSuccess(self, r):
+ """
+ Callback for a successful send.
+
+ :param r: The result from the last previous callback in the chain.
+ :type r: anything
+ """
+ log.msg(r)
+ signal(proto.SMTP_SEND_MESSAGE_SUCCESS, self._user.dest.addrstr)
+
+ def sendError(self, e):
+ """
+ Callback for an unsuccessfull send.
+
+ :param e: The result from the last errback.
+ :type e: anything
+ """
+ log.msg(e)
+ log.err()
+ signal(proto.SMTP_SEND_MESSAGE_ERROR, self._user.dest.addrstr)
+
+ def sendMessage(self):
+ """
+ Send the message.
+
+ This method will prepare the message (headers and possibly encrypted
+ body) and send it using the ESMTPSenderFactory.
+
+ @return: A deferred with callbacks for error and success of this
+ message send.
+ @rtype: twisted.internet.defer.Deferred
+ """
+ msg = self._msg.as_string(False)
+
+ log.msg("Connecting to SMTP server %s:%s" % (self._host, self._port))
+
+ d = defer.Deferred()
+ # we don't pass an ssl context factory to the ESMTPSenderFactory
+ # because ssl will be handled by reactor.connectSSL() below.
+ factory = smtp.ESMTPSenderFactory(
+ "", # username is blank because server does not use auth.
+ "", # password is blank because server does not use auth.
+ self._fromAddress.addrstr,
+ self._user.dest.addrstr,
+ StringIO(msg),
+ d,
+ requireAuthentication=False,
+ requireTransportSecurity=True)
+ signal(proto.SMTP_SEND_MESSAGE_START, self._user.dest.addrstr)
+ reactor.connectSSL(
+ self._host, self._port, factory,
+ contextFactory=SSLContextFactory(self._cert, self._key))
+ d.addCallback(self.sendSuccess)
+ d.addErrback(self.sendError)
+ return d
+
+ #
+ # encryption methods
+ #
+
+ def _encrypt_and_sign(self, pubkey, signkey):
+ """
+ Create an RFC 3156 compliang PGP encrypted and signed message using
+ C{pubkey} to encrypt and C{signkey} to sign.
+
+ :param pubkey: The public key used to encrypt the message.
+ :type pubkey: leap.common.keymanager.openpgp.OpenPGPKey
+ :param signkey: The private key used to sign the message.
+ :type signkey: leap.common.keymanager.openpgp.OpenPGPKey
+ """
+ # create new multipart/encrypted message with 'pgp-encrypted' protocol
+ newmsg = MultipartEncrypted('application/pgp-encrypted')
+ # move (almost) all headers from original message to the new message
+ move_headers(self._origmsg, newmsg)
+ # create 'application/octet-stream' encrypted message
+ encmsg = MIMEApplication(
+ self._km.encrypt(self._origmsg.as_string(unixfrom=False), pubkey,
+ sign=signkey),
+ _subtype='octet-stream', _encoder=lambda x: x)
+ encmsg.add_header('content-disposition', 'attachment',
+ filename='msg.asc')
+ # create meta message
+ metamsg = PGPEncrypted()
+ metamsg.add_header('Content-Disposition', 'attachment')
+ # attach pgp message parts to new message
+ newmsg.attach(metamsg)
+ newmsg.attach(encmsg)
+ self._msg = newmsg
+
+ def _sign(self, signkey):
+ """
+ Create an RFC 3156 compliant PGP signed MIME message using C{signkey}.
+
+ :param signkey: The private key used to sign the message.
+ :type signkey: leap.common.keymanager.openpgp.OpenPGPKey
+ """
+ # create new multipart/signed message
+ newmsg = MultipartSigned('application/pgp-signature', 'pgp-sha512')
+ # move (almost) all headers from original message to the new message
+ move_headers(self._origmsg, newmsg)
+ # apply base64 content-transfer-encoding
+ encode_base64_rec(self._origmsg)
+ # get message text with headers and replace \n for \r\n
+ fp = StringIO()
+ g = RFC3156CompliantGenerator(
+ fp, mangle_from_=False, maxheaderlen=76)
+ g.flatten(self._origmsg)
+ msgtext = re.sub('\r?\n', '\r\n', fp.getvalue())
+ # make sure signed message ends with \r\n as per OpenPGP stantard.
+ if self._origmsg.is_multipart():
+ if not msgtext.endswith("\r\n"):
+ msgtext += "\r\n"
+ # calculate signature
+ signature = self._km.sign(msgtext, signkey, digest_algo='SHA512',
+ clearsign=False, detach=True, binary=False)
+ sigmsg = PGPSignature(signature)
+ # attach original message and signature to new message
+ newmsg.attach(self._origmsg)
+ newmsg.attach(sigmsg)
+ self._msg = newmsg
+
+ def _maybe_encrypt_and_sign(self):
+ """
+ Attempt to encrypt and sign the outgoing message.
+
+ The behaviour of this method depends on:
+
+ 1. the original message's content-type, and
+ 2. the availability of the recipient's public key.
+
+ If the original message's content-type is "multipart/encrypted", then
+ the original message is not altered. For any other content-type, the
+ method attempts to fetch the recipient's public key. If the
+ recipient's public key is available, the message is encrypted and
+ signed; otherwise it is only signed.
+
+ Note that, if the C{encrypted_only} configuration is set to True and
+ the recipient's public key is not available, then the recipient
+ address would have been rejected in SMTPDelivery.validateTo().
+
+ The following table summarizes the overall behaviour of the gateway:
+
+ +---------------------------------------------------+----------------+
+ | content-type | rcpt pubkey | enforce encr. | action |
+ +---------------------+-------------+---------------+----------------+
+ | multipart/encrypted | any | any | pass |
+ | other | available | any | encrypt + sign |
+ | other | unavailable | yes | reject |
+ | other | unavailable | no | sign |
+ +---------------------+-------------+---------------+----------------+
+ """
+ # pass if the original message's content-type is "multipart/encrypted"
+ self._origmsg = self.parseMessage()
+ if self._origmsg.get_content_type() == 'multipart/encrypted':
+ self._msg = self._origmsg
+ return
+
+ from_address = validate_address(self._fromAddress.addrstr)
+ signkey = self._km.get_key(from_address, OpenPGPKey, private=True)
+ log.msg("Will sign the message with %s." % signkey.fingerprint)
+ to_address = validate_address(self._user.dest.addrstr)
+ try:
+ # try to get the recipient pubkey
+ pubkey = self._km.get_key(to_address, OpenPGPKey)
+ log.msg("Will encrypt the message to %s." % pubkey.fingerprint)
+ signal(proto.SMTP_START_ENCRYPT_AND_SIGN,
+ "%s,%s" % (self._fromAddress.addrstr, to_address))
+ self._encrypt_and_sign(pubkey, signkey)
+ signal(proto.SMTP_END_ENCRYPT_AND_SIGN,
+ "%s,%s" % (self._fromAddress.addrstr, to_address))
+ except KeyNotFound:
+ # at this point we _can_ send unencrypted mail, because if the
+ # configuration said the opposite the address would have been
+ # rejected in SMTPDelivery.validateTo().
+ log.msg('Will send unencrypted message to %s.' % to_address)
+ signal(proto.SMTP_START_SIGN, self._fromAddress.addrstr)
+ self._sign(signkey)
+ signal(proto.SMTP_END_SIGN, self._fromAddress.addrstr)