import re import gnupg from zope.interface import implements from StringIO import StringIO from twisted.mail import smtp from twisted.internet.protocol import ServerFactory from twisted.internet import reactor from twisted.internet import defer from twisted.application import internet, service from twisted.python import log from email.Header import Header class SMTPFactory(ServerFactory): """ Factory for an SMTP server with encrypted relaying capabilities. """ def __init__(self, gpg=None): self._gpg = gpg def buildProtocol(self, addr): "Return a protocol suitable for the job." # TODO: use ESMTP here. smtpProtocol = smtp.SMTP(SMTPDelivery(self._gpg)) smtpProtocol.factory = self return smtpProtocol class SMTPDelivery(object): """ Validate email addresses and handle message delivery. """ implements(smtp.IMessageDelivery) def __init__(self, gpg=None): if gpg: self._gpg = gpg else: self._gpg = GPGWrapper() def receivedHeader(self, helo, origin, recipients): 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): """Assert existence of and trust on recipient's GPG public key.""" # try to find recipient's public key try: # this will raise an exception if key is not found trust = self._gpg.find_key(user.dest.addrstr)['trust'] # if key is not ultimatelly trusted, then the message will not # be encrypted. So, we check for this below #if trust != 'u': # raise smtp.SMTPBadRcpt(user) log.msg("Accepting mail for %s..." % user.dest) return lambda: EncryptedMessage(user, gpg=self._gpg) except LookupError: raise smtp.SMTPBadRcpt(user) def validateFrom(self, helo, originAddress): # accept mail from anywhere. To reject an address, raise # smtp.SMTPBadSender here. return originAddress class EncryptedMessage(): """ Receive plaintext from client, encrypt it and send message to a recipient. """ implements(smtp.IMessage) SMTP_HOSTNAME = "mail.riseup.net" SMTP_PORT = 25 def __init__(self, user, gpg=None): self.user = user self.getSMTPInfo() self.lines = [] if gpg: self._gpg = gpg else: self._gpg = GPGWrapper() def lineReceived(self, line): """Store email DATA lines as they arrive.""" self.lines.append(line) def eomReceived(self): """Encrypt and send message.""" log.msg("Message data complete.") self.lines.append('') # add a trailing newline self.parseMessage() try: self.encrypt() return self.sendMessage() except LookupError: return None def parseMessage(self): """Separate message headers from body.""" sep = self.lines.index('') self.headers = self.lines[:sep] self.body = self.lines[sep+1:] def connectionLost(self): log.msg("Connection lost unexpectedly!") log.err() # unexpected loss of connection; don't save self.lines = [] def sendSuccess(self, r): log.msg(r) def sendError(self, e): log.msg(e) log.err() def prepareHeader(self): self.headers.insert(1, "From: %s" % self.user.orig.addrstr) self.headers.insert(2, "To: %s" % self.user.dest.addrstr) self.headers.append('') def sendMessage(self): self.prepareHeader() msg = '\n'.join(self.headers+[self.cyphertext]) d = defer.Deferred() factory = smtp.ESMTPSenderFactory(self.smtp_username, self.smtp_password, self.smtp_username, self.user.dest.addrstr, StringIO(msg), d) # the next call is TSL-powered! reactor.connectTCP(self.SMTP_HOSTNAME, self.SMTP_PORT, factory) d.addCallback(self.sendSuccess) d.addErrback(self.sendError) return d def encrypt(self, always_trust=True): # TODO: do not "always trust" here. fp = self._gpg.find_key(self.user.dest.addrstr)['fingerprint'] log.msg("Encrypting to %s" % fp) self.cyphertext = str(self._gpg.encrypt('\n'.join(self.body), [fp], always_trust=always_trust)) # this will be replaced by some other mechanism of obtaining credentials # for SMTP server. def getSMTPInfo(self): f = open('/media/smtp-info.txt', 'r') self.smtp_host = f.readline().rstrip() self.smtp_port = f.readline().rstrip() self.smtp_username = f.readline().rstrip() self.smtp_password = f.readline().rstrip() f.close() class GPGWrapper(): """ This is a temporary class for handling GPG requests, and should be replaced by a more general class used throughout the project. """ GNUPG_HOME = "~/.config/leap/gnupg" GNUPG_BINARY = "/usr/bin/gpg" # TODO: change this based on OS def __init__(self, gpghome=GNUPG_HOME, gpgbinary=GNUPG_BINARY): self.gpg = gnupg.GPG(gnupghome=gpghome, gpgbinary=gpgbinary) def find_key(self, email): """ Find user's key based on their email. """ for key in self.gpg.list_keys(): for uid in key['uids']: if re.search(email, uid): return key raise LookupError("GnuPG public key for %s not found!" % email) def encrypt(self, data, recipient, always_trust=True): # TODO: do not 'always_trust'. return self.gpg.encrypt(data, recipient, always_trust=always_trust) def decrypt(self, data): return self.gpg.decrypt(data) def import_keys(self, data): return self.gpg.import_keys(data) # service configuration port = 25 factory = SMTPFactory() # these enable the use of this service with twistd application = service.Application("LEAP SMTP Relay") service = internet.TCPServer(port, factory) service.setServiceParent(application)