Merge branch 'feature/smtp-relay' into develop

1 files changed, 203 insertions, 0 deletions

diff --git a/src/leap/email/smtp/smtprelay.py b/src/leap/email/smtp/smtprelay.py
new file mode 100644
index 00000000..f44aeb6f
--- /dev/null
+++ b/src/leap/email/smtp/smtprelay.py
@@ -0,0 +1,203 @@
+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" # this has to be changed 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)