# -*- 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 . """ 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.internet.threads import deferToThread 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 import __version__ 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 # LOCAL_FQDN = "bitmask.local" 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 SMTPHeloLocalhost(smtp.SMTP): """ An SMTP class that ensures a proper FQDN for localhost. This avoids a problem in which unproperly configured providers would complain about the helo not being a fqdn. """ def __init__(self, *args): smtp.SMTP.__init__(self, *args) self.host = LOCAL_FQDN class SMTPFactory(ServerFactory): """ Factory for an SMTP server with encrypted gatewaying capabilities. """ domain = LOCAL_FQDN 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 = SMTPHeloLocalhost(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._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 bitmask.local from %s with ESMTP ; %s" % ( clientIP, smtp.rfc822date()) # email.Header.Header used for automatic wrapping of long lines return "Received: %s" % Header(s=headerValue, header_name='Received') 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 class EncryptedMessage(object): """ Receive plaintext from client, encrypt it and send message to a recipient. """ implements(smtp.IMessage) FOOTER_STRING = "I prefer encrypted email" 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. :returns: a deferred """ log.msg("Message data complete.") self.lines.append('') # add a trailing newline d = deferToThread(self._maybe_encrypt_and_sign) d.addCallbacks(self.sendMessage, self.skipNoKeyErrBack) return d 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 = [] # ends IMessage implementation def skipNoKeyErrBack(self, failure): """ Errback that ignores a KeyNotFound :param failure: the failure :type Failure: Failure """ err = failure.value if failure.check(KeyNotFound): pass else: raise err def parseMessage(self): """ Separate message headers from body. """ parser = Parser() return parser.parsestr('\r\n'.join(self.lines)) def sendQueued(self, r): """ Callback for the queued message. :param r: The result from the last previous callback in the chain. :type r: anything """ log.msg(r) 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, failure): """ Callback for an unsuccessfull send. :param e: The result from the last errback. :type e: anything """ signal(proto.SMTP_SEND_MESSAGE_ERROR, self._user.dest.addrstr) err = failure.value log.err(err) raise err def sendMessage(self, *args): """ Sends the message. :return: A deferred with callback and errback for this #message send. :rtype: twisted.internet.defer.Deferred """ d = deferToThread(self._route_msg) d.addCallbacks(self.sendQueued, self.sendError) return d def _route_msg(self): """ Sends the msg using the ESMTPSenderFactory. """ log.msg("Connecting to SMTP server %s:%s" % (self._host, self._port)) msg = self._msg.as_string(False) # we construct a defer to pass to the ESMTPSenderFactory d = defer.Deferred() d.addCallbacks(self.sendSuccess, self.sendError) # 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, heloFallback=True, requireAuthentication=False, requireTransportSecurity=True) factory.domain = __version__ signal(proto.SMTP_SEND_MESSAGE_START, self._user.dest.addrstr) reactor.connectSSL( self._host, self._port, factory, contextFactory=SSLContextFactory(self._cert, self._key)) # # 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: OpenPGPKey :param signkey: The private key used to sign the message. :type signkey: 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 self._fix_headers(self._origmsg, newmsg, signkey) # 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 self._fix_headers(self._origmsg, newmsg, signkey) # 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) username, domain = from_address.split('@') # add a nice footer to the outgoing message if self._origmsg.get_content_type() == 'text/plain': self.lines.append('--') self.lines.append('%s - https://%s/key/%s' % (self.FOOTER_STRING, domain, username)) self.lines.append('') self._origmsg = self.parseMessage() # get sender and recipient data 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) def _fix_headers(self, origmsg, newmsg, signkey): """ Move some headers from C{origmsg} to C{newmsg}, delete unwanted headers from C{origmsg} and add new headers to C{newms}. Outgoing messages are either encrypted and signed or just signed before being sent. Because of that, they are packed inside new messages and some manipulation has to be made on their headers. Allowed headers for passing through: - From - Date - To - Subject - Reply-To - References - In-Reply-To - Cc Headers to be added: - Message-ID (i.e. should not use origmsg's Message-Id) - Received (this is added automatically by twisted smtp API) - OpenPGP (see #4447) Headers to be deleted: - User-Agent :param origmsg: The original message. :type origmsg: email.message.Message :param newmsg: The new message being created. :type newmsg: email.message.Message :param signkey: The key used to sign C{newmsg} :type signkey: OpenPGPKey """ # move headers from origmsg to newmsg headers = origmsg.items() passthrough = [ 'from', 'date', 'to', 'subject', 'reply-to', 'references', 'in-reply-to', 'cc' ] headers = filter(lambda x: x[0].lower() in passthrough, headers) for hkey, hval in headers: newmsg.add_header(hkey, hval) del(origmsg[hkey]) # add a new message-id to newmsg newmsg.add_header('Message-Id', smtp.messageid()) # add openpgp header to newmsg username, domain = signkey.address.split('@') newmsg.add_header( 'OpenPGP', 'id=%s' % signkey.key_id, url='https://%s/key/%s' % (domain, username), preference='signencrypt') # delete user-agent from origmsg del(origmsg['user-agent'])