Make smtp-relay sign all outgoing message.

* Update docstrings.
* Remove prepareHeader and its bug.
* Make smtp-relay always sign outgoing mail.

4 files changed, 235 insertions, 103 deletions

diff --git a/mail/src/leap/mail/smtp/__init__.py b/mail/src/leap/mail/smtp/__init__.py
index 13af0156..ace79b5f 100644
--- a/mail/src/leap/mail/smtp/__init__.py
+++ b/mail/src/leap/mail/smtp/__init__.py
@@ -31,7 +31,7 @@ from leap.mail.smtp.smtprelay import SMTPFactory
 
 
 def setup_smtp_relay(port, keymanager, smtp_host, smtp_port, smtp_username,
-                    smtp_password, encrypted_only):
+                     smtp_password, encrypted_only):
     """
     Setup SMTP relay to run with Twisted.
 
diff --git a/mail/src/leap/mail/smtp/smtprelay.py b/mail/src/leap/mail/smtp/smtprelay.py
index bd18fb56..d87dc87b 100644
--- a/mail/src/leap/mail/smtp/smtprelay.py
+++ b/mail/src/leap/mail/smtp/smtprelay.py
@@ -40,11 +40,11 @@ from email.parser import Parser
 from leap.common.check import leap_assert, leap_assert_type
 from leap.common.keymanager import KeyManager
 from leap.common.keymanager.openpgp import (
-    encrypt_asym,
     OpenPGPKey,
+    encrypt_asym,
+    sign,
 )
 from leap.common.keymanager.errors import KeyNotFound
-from leap.common.keymanager.keys import is_address
 
 
 #
@@ -103,31 +103,25 @@ def assert_config_structure(config):
     leap_assert(config[PASSWORD_KEY] != '')
 
 
-def strip_and_validate_address(address):
+def validate_address(address):
     """
-    Helper function to (eventually) strip and validate an email address.
-
-    This function first checks whether the incomming C{address} is of the form
-    '<something>' and, if it is, then '<' and '>' are removed from the
-    address. After that, a simple validation for user@provider form is
-    carried.
+    Validate C{address} as defined in RFC 2822.
 
     @param address: The address to be validated.
     @type address: str
 
-    @return: The (eventually) stripped address.
+    @return: A valid address.
     @rtype: str
 
-    @raise smtp.SMTPBadRcpt: Raised if C{address} does not have the expected
-        format.
+    @raise smtp.SMTPBadRcpt: Raised if C{address} is invalid.
     """
-    leap_assert(address is not None)
     leap_assert_type(address, str)
+    # the following parses the address as described in RFC 2822 and
+    # returns ('', '') if the parse fails.
     _, address = parseaddr(address)
-    leap_assert(address != '')
-    if is_address(address):
-        return address
-    raise smtp.SMTPBadRcpt(address)
+    if address == '':
+        raise smtp.SMTPBadRcpt(address)
+    return address
 
 
 #
@@ -141,6 +135,8 @@ class SMTPFactory(ServerFactory):
 
     def __init__(self, keymanager, config):
         """
+        Initialize the SMTP factory.
+
         @param keymanager: A KeyManager for retrieving recipient's keys.
         @type keymanager: leap.common.keymanager.KeyManager
         @param config: A dictionary with smtp configuration. Should have
@@ -190,6 +186,8 @@ class SMTPDelivery(object):
 
     def __init__(self, keymanager, config):
         """
+        Initialize the SMTP delivery object.
+
         @param keymanager: A KeyManager for retrieving recipient's keys.
         @type keymanager: leap.common.keymanager.KeyManager
         @param config: A dictionary with smtp configuration. Should have
@@ -209,10 +207,11 @@ class SMTPDelivery(object):
         # and store them
         self._km = keymanager
         self._config = config
+        self._origin = None
 
     def receivedHeader(self, helo, origin, recipients):
         """
-        Generate the Received header for a message.
+        Generate the 'Received:' header for a message.
 
         @param helo: The argument to the HELO command and the client's IP
             address.
@@ -234,12 +233,17 @@ class SMTPDelivery(object):
 
     def validateTo(self, user):
         """
-        Validate the address for which the message is destined.
+        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.
 
-        For now, it just asserts the existence of the user's key if the
-        configuration option ENCRYPTED_ONLY_KEY is True.
+        In the end, it returns an encrypted message object that is able to
+        send itself to the C{user}'s address.
 
-        @param user: The address to validate.
+        @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
@@ -253,7 +257,7 @@ class SMTPDelivery(object):
         """
         # try to find recipient's public key
         try:
-            address = strip_and_validate_address(user.dest.addrstr)
+            address = validate_address(user.dest.addrstr)
             pubkey = self._km.get_key(address, OpenPGPKey)
             log.msg("Accepting mail for %s..." % user.dest)
         except KeyNotFound:
@@ -262,7 +266,8 @@ class SMTPDelivery(object):
                 raise smtp.SMTPBadRcpt(user.dest.addrstr)
             log.msg("Warning: will send an unencrypted message (because "
                     "encrypted_only' is set to False).")
-        return lambda: EncryptedMessage(user, self._km, self._config)
+        return lambda: EncryptedMessage(
+            self._origin, user, self._km, self._config)
 
     def validateFrom(self, helo, origin):
         """
@@ -282,6 +287,7 @@ class SMTPDelivery(object):
         """
         # accept mail from anywhere. To reject an address, raise
         # smtp.SMTPBadSender here.
+        self._origin = origin
         return origin
 
 
@@ -296,12 +302,14 @@ class EncryptedMessage(object):
     """
     implements(smtp.IMessage)
 
-    def __init__(self, user, keymanager, config):
+    def __init__(self, fromAddress, user, keymanager, config):
         """
         Initialize the encrypted message.
 
-        @param user: The address to validate.
-        @type: twisted.mail.smtp.User
+        @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 config: A dictionary with smtp configuration. Should have
@@ -320,6 +328,7 @@ class EncryptedMessage(object):
         leap_assert_type(keymanager, KeyManager)
         assert_config_structure(config)
         # and store them
+        self._fromAddress = fromAddress
         self._user = user
         self._km = keymanager
         self._config = config
@@ -345,7 +354,7 @@ class EncryptedMessage(object):
         self.lines.append('')  # add a trailing newline
         self.parseMessage()
         try:
-            self._encrypt()
+            self._encrypt_and_sign()
             return self.sendMessage()
         except KeyNotFound:
             return None
@@ -385,12 +394,6 @@ class EncryptedMessage(object):
         log.msg(e)
         log.err()
 
-    def prepareHeader(self):
-        """
-        Prepare the headers of the message.
-        """
-        self._message.replace_header('From', '<%s>' % self._user.orig.addrstr)
-
     def sendMessage(self):
         """
         Send the message.
@@ -402,7 +405,6 @@ class EncryptedMessage(object):
             message send.
         @rtype: twisted.internet.defer.Deferred
         """
-        self.prepareHeader()
         msg = self._message.as_string(False)
         d = defer.Deferred()
         factory = smtp.ESMTPSenderFactory(
@@ -424,26 +426,50 @@ class EncryptedMessage(object):
         d.addErrback(self.sendError)
         return d
 
-    def _encrypt_payload_rec(self, message, pubkey):
+    def _encrypt_and_sign_payload_rec(self, message, pubkey, signkey):
         """
-        Recursivelly descend in C{message}'s payload and encrypt to C{pubkey}.
+        Recursivelly descend in C{message}'s payload encrypting to C{pubkey}
+        and signing with C{signkey}.
 
         @param message: The message whose payload we want to encrypt.
         @type message: email.message.Message
         @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
         """
         if message.is_multipart() is False:
-            message.set_payload(encrypt_asym(message.get_payload(), pubkey))
+            message.set_payload(
+                encrypt_asym(
+                    message.get_payload(), pubkey, sign=signkey))
         else:
             for msg in message.get_payload():
-                self._encrypt_payload_rec(msg, pubkey)
+                self._encrypt_and_sign_payload_rec(msg, pubkey, signkey)
 
-    def _encrypt(self):
+    def _sign_payload_rec(self, message, signkey):
+        """
+        Recursivelly descend in C{message}'s payload signing with C{signkey}.
+
+        @param message: The message whose payload we want to encrypt.
+        @type message: email.message.Message
+        @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
+        """
+        if message.is_multipart() is False:
+            message.set_payload(
+                sign(
+                    message.get_payload(), signkey))
+        else:
+            for msg in message.get_payload():
+                self._sign_payload_rec(msg, signkey)
+
+    def _encrypt_and_sign(self):
         """
         Encrypt the message body.
 
-        This method fetches the recipient key and encrypts the content to the
+        Fetch the recipient key and encrypt the content to the
         recipient. If a key is not found, then the behaviour depends on the
         configuration parameter ENCRYPTED_ONLY_KEY. If it is False, the message
         is sent unencrypted and a warning is logged. If it is True, the
@@ -452,13 +478,18 @@ class EncryptedMessage(object):
         @raise KeyNotFound: Raised when the recipient key was not found and
             the ENCRYPTED_ONLY_KEY configuration parameter is set to True.
         """
+        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:
-            address = strip_and_validate_address(self._user.dest.addrstr)
-            pubkey = self._km.get_key(address, OpenPGPKey)
-            log.msg("Encrypting to %s" % pubkey.fingerprint)
-            self._encrypt_payload_rec(self._message, pubkey)
+            # try to get the recipient pubkey
+            pubkey = self._km.get_key(to_address, OpenPGPKey)
+            log.msg("Will encrypt the message to %s." % pubkey.fingerprint)
+            self._encrypt_and_sign_payload_rec(self._message, pubkey, signkey)
         except KeyNotFound:
-            if self._config[ENCRYPTED_ONLY_KEY]:
-                raise
-            log.msg("Warning: sending unencrypted mail (because "
-                    "'encrypted_only' is set to False).")
+            # at this point we _can_ send unencrypted mail, because if the
+            # configuration said the opposite the address would have been
+            # rejected in SMTPDelivery.validateTo().
+            self._sign_payload_rec(self._message, signkey)
+            log.msg('Will send unencrypted message to %s.' % to_address)
diff --git a/mail/src/leap/mail/tests/smtp/__init__.py b/mail/src/leap/mail/tests/smtp/__init__.py
index 113e0473..c69c34f0 100644
--- a/mail/src/leap/mail/tests/smtp/__init__.py
+++ b/mail/src/leap/mail/tests/smtp/__init__.py
@@ -106,6 +106,9 @@ class TestCaseWithKeyManager(BaseLeapTest):
 
 # Key material for testing
 KEY_FINGERPRINT = "E36E738D69173C13D709E44F2F455E2824D18DDF"
+
+ADDRESS = 'leap@leap.se'
+
 PUBLIC_KEY = """
 -----BEGIN PGP PUBLIC KEY BLOCK-----
 Version: GnuPG v1.4.10 (GNU/Linux)
@@ -159,6 +162,7 @@ ZtQ/VymwFL3XdUWV6B/hU4PVAFvO3qlOtdJ6TpE+nEWgcWjCv5g7RjXX
 =MuOY
 -----END PGP PUBLIC KEY BLOCK-----
 """
+
 PRIVATE_KEY = """
 -----BEGIN PGP PRIVATE KEY BLOCK-----
 Version: GnuPG v1.4.10 (GNU/Linux)
@@ -266,3 +270,64 @@ RZXoH+FTg9UAW87eqU610npOkT6cRaBxaMK/mDtGNdc=
 =JTFu
 -----END PGP PRIVATE KEY BLOCK-----
 """
+
+ADDRESS_2 = 'anotheruser@leap.se'
+
+PUBLIC_KEY_2 = """
+-----BEGIN PGP PUBLIC KEY BLOCK-----
+Version: GnuPG v1.4.10 (GNU/Linux)
+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=
+=Thdu
+-----END PGP PUBLIC KEY BLOCK-----
+"""
+
+PRIVATE_KEY_2 = """
+-----BEGIN PGP PRIVATE KEY BLOCK-----
+Version: GnuPG v1.4.10 (GNU/Linux)
+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+=a5gs
+-----END PGP PRIVATE KEY BLOCK-----
+"""
+
diff --git a/mail/src/leap/mail/tests/smtp/test_smtprelay.py b/mail/src/leap/mail/tests/smtp/test_smtprelay.py
index 6ef4e853..e48f1291 100644
--- a/mail/src/leap/mail/tests/smtp/test_smtprelay.py
+++ b/mail/src/leap/mail/tests/smtp/test_smtprelay.py
@@ -28,6 +28,7 @@ from datetime import datetime
 from twisted.test import proto_helpers
 from twisted.mail.smtp import (
     User,
+    Address,
     SMTPBadRcpt,
 )
 from mock import Mock
@@ -37,7 +38,11 @@ from leap.mail.smtp.smtprelay import (
     SMTPFactory,
     EncryptedMessage,
 )
-from leap.mail.tests.smtp import TestCaseWithKeyManager
+from leap.mail.tests.smtp import (
+    TestCaseWithKeyManager,
+    ADDRESS,
+    ADDRESS_2,
+)
 from leap.common.keymanager import openpgp
 
 
@@ -52,11 +57,11 @@ IP_OR_HOST_REGEX = '(' + IP_REGEX + '|' + HOSTNAME_REGEX + ')'
 class TestSmtpRelay(TestCaseWithKeyManager):
 
     EMAIL_DATA = ['HELO relay.leap.se',
-                  'MAIL FROM: <user@leap.se>',
-                  'RCPT TO: <leap@leap.se>',
+                  'MAIL FROM: <%s>' % ADDRESS_2,
+                  'RCPT TO: <%s>' % ADDRESS,
                   'DATA',
-                  'From: User <user@leap.se>',
-                  'To: Leap <leap@leap.se>',
+                  'From: User <%s>' % ADDRESS_2,
+                  'To: Leap <%s>' % ADDRESS,
                   'Date: ' + datetime.now().strftime('%c'),
                   'Subject: test message',
                   '',
@@ -77,13 +82,15 @@ class TestSmtpRelay(TestCaseWithKeyManager):
         "Test if openpgp can encrypt and decrypt."
         text = "simple raw text"
         pubkey = self._km.get_key(
-            'leap@leap.se', openpgp.OpenPGPKey, private=False)
+            ADDRESS, openpgp.OpenPGPKey, private=False)
         encrypted = openpgp.encrypt_asym(text, pubkey)
-        self.assertNotEqual(text, encrypted, "failed encrypting text")
+        self.assertNotEqual(
+            text, encrypted, "Ciphertext is equal to plaintext.")
         privkey = self._km.get_key(
-            'leap@leap.se', openpgp.OpenPGPKey, private=True)
+            ADDRESS, openpgp.OpenPGPKey, private=True)
         decrypted = openpgp.decrypt_asym(encrypted, privkey)
-        self.assertEqual(text, decrypted, "failed decrypting text")
+        self.assertEqual(text, decrypted,
+            "Decrypted text differs from plaintext.")
 
     def test_relay_accepts_valid_email(self):
         """
@@ -104,7 +111,8 @@ class TestSmtpRelay(TestCaseWithKeyManager):
         for i, line in enumerate(self.EMAIL_DATA):
             proto.lineReceived(line + '\r\n')
             self.assertMatch(transport.value(),
-                             '\r\n'.join(SMTP_ANSWERS[0:i + 1]))
+                             '\r\n'.join(SMTP_ANSWERS[0:i + 1]),
+                             'Did not get expected answer from relay.')
         proto.setTimeout(None)
 
     def test_message_encrypt(self):
@@ -113,17 +121,77 @@ class TestSmtpRelay(TestCaseWithKeyManager):
         """
         proto = SMTPFactory(
             self._km, self._config).buildProtocol(('127.0.0.1', 0))
-        user = User('leap@leap.se', 'relay.leap.se', proto, 'leap@leap.se')
-        m = EncryptedMessage(user, self._km, self._config)
+        fromAddr = Address(ADDRESS_2)
+        dest = User(ADDRESS, 'relay.leap.se', proto, ADDRESS)
+        m = EncryptedMessage(fromAddr, dest, self._km, self._config)
         for line in self.EMAIL_DATA[4:12]:
             m.lineReceived(line)
         m.eomReceived()
         privkey = self._km.get_key(
-            'leap@leap.se', openpgp.OpenPGPKey, private=True)
+            ADDRESS, openpgp.OpenPGPKey, private=True)
         decrypted = openpgp.decrypt_asym(m._message.get_payload(), privkey)
         self.assertEqual(
             '\r\n'.join(self.EMAIL_DATA[9:12]) + '\r\n',
-            decrypted)
+            decrypted,
+            'Decrypted text differs from plaintext.')
+
+    def test_message_encrypt_sign(self):
+        """
+        Test if message gets encrypted to destination email and signed with
+        sender key.
+        """
+        proto = SMTPFactory(
+            self._km, self._config).buildProtocol(('127.0.0.1', 0))
+        user = User(ADDRESS, 'relay.leap.se', proto, ADDRESS)
+        fromAddr = Address(ADDRESS_2)
+        m = EncryptedMessage(fromAddr, user, self._km, self._config)
+        for line in self.EMAIL_DATA[4:12]:
+            m.lineReceived(line)
+        # trigger encryption and signing
+        m.eomReceived()
+        # decrypt and verify
+        privkey = self._km.get_key(
+            ADDRESS, openpgp.OpenPGPKey, private=True)
+        pubkey = self._km.get_key(ADDRESS_2, openpgp.OpenPGPKey)
+        decrypted = openpgp.decrypt_asym(
+            m._message.get_payload(), privkey, verify=pubkey)
+        self.assertEqual(
+            '\r\n'.join(self.EMAIL_DATA[9:12]) + '\r\n',
+            decrypted,
+            'Decrypted text differs from plaintext.')
+
+    def test_message_sign(self):
+        """
+        Test if message is signed with sender key.
+        """
+        # mock the key fetching
+        self._km.fetch_keys_from_server = Mock(return_value=[])
+        proto = SMTPFactory(
+            self._km, self._config).buildProtocol(('127.0.0.1', 0))
+        user = User('ihavenopubkey@nonleap.se', 'relay.leap.se', proto, ADDRESS)
+        fromAddr = Address(ADDRESS_2)
+        m = EncryptedMessage(fromAddr, user, self._km, self._config)
+        for line in self.EMAIL_DATA[4:12]:
+            m.lineReceived(line)
+        # trigger signing
+        m.eomReceived()
+        # assert content of message
+        self.assertTrue(
+            m._message.get_payload().startswith(
+                '-----BEGIN PGP SIGNED MESSAGE-----\n' +
+                'Hash: SHA1\n\n' + 
+                ('\r\n'.join(self.EMAIL_DATA[9:12]) + '\r\n' +
+                '-----BEGIN PGP SIGNATURE-----\n')),
+            'Message does not start with signature header.')
+        self.assertTrue(
+            m._message.get_payload().endswith(
+                '-----END PGP SIGNATURE-----\n'),
+            'Message does not end with signature footer.')
+        # assert signature is valid
+        pubkey = self._km.get_key(ADDRESS_2, openpgp.OpenPGPKey)
+        self.assertTrue(
+            openpgp.verify(m._message.get_payload(), pubkey),
+            'Signature could not be verified.')
 
     def test_missing_key_rejects_address(self):
         """
@@ -131,7 +199,7 @@ class TestSmtpRelay(TestCaseWithKeyManager):
         True.
         """
         # remove key from key manager
-        pubkey = self._km.get_key('leap@leap.se', openpgp.OpenPGPKey)
+        pubkey = self._km.get_key(ADDRESS, openpgp.OpenPGPKey)
         pgp = openpgp.OpenPGPScheme(self._soledad)
         pgp.delete_key(pubkey)
         # mock the key fetching
@@ -148,7 +216,8 @@ class TestSmtpRelay(TestCaseWithKeyManager):
         lines = transport.value().rstrip().split('\n')
         self.assertEqual(
             '550 Cannot receive for specified address',
-            lines[-1])
+            lines[-1],
+            'Address should have been rejecetd with appropriate message.')
 
     def test_missing_key_accepts_address(self):
         """
@@ -156,7 +225,7 @@ class TestSmtpRelay(TestCaseWithKeyManager):
         False.
         """
         # remove key from key manager
-        pubkey = self._km.get_key('leap@leap.se', openpgp.OpenPGPKey)
+        pubkey = self._km.get_key(ADDRESS, openpgp.OpenPGPKey)
         pgp = openpgp.OpenPGPScheme(self._soledad)
         pgp.delete_key(pubkey)
         # mock the key fetching
@@ -171,42 +240,9 @@ class TestSmtpRelay(TestCaseWithKeyManager):
         proto.lineReceived(self.EMAIL_DATA[0] + '\r\n')
         proto.lineReceived(self.EMAIL_DATA[1] + '\r\n')
         proto.lineReceived(self.EMAIL_DATA[2] + '\r\n')
-        # ensure the address was rejected
+        # ensure the address was accepted
         lines = transport.value().rstrip().split('\n')
         self.assertEqual(
             '250 Recipient address accepted',
-            lines[-1])
-
-    def test_malformed_address_rejects(self):
-        """
-        Test if server rejects to send to malformed addresses.
-        """
-        # mock the key fetching
-        self._km.fetch_keys_from_server = Mock(return_value=[])
-        # prepare the SMTP factory
-        for malformed in ['leap@']:
-            proto = SMTPFactory(
-                self._km, self._config).buildProtocol(('127.0.0.1', 0))
-            transport = proto_helpers.StringTransport()
-            proto.makeConnection(transport)
-            proto.lineReceived(self.EMAIL_DATA[0] + '\r\n')
-            proto.lineReceived(self.EMAIL_DATA[1] + '\r\n')
-            proto.lineReceived('RCPT TO: <%s>%s' % (malformed, '\r\n'))
-            # ensure the address was rejected
-            lines = transport.value().rstrip().split('\n')
-            self.assertEqual(
-                '550 Cannot receive for specified address',
-                lines[-1])
-
-    def test_prepare_header_adds_from(self):
-        """
-        Test if message headers are OK.
-        """
-        proto = SMTPFactory(
-            self._km, self._config).buildProtocol(('127.0.0.1', 0))
-        user = User('leap@leap.se', 'relay.leap.se', proto, 'leap@leap.se')
-        m = EncryptedMessage(user, self._km, self._config)
-        for line in self.EMAIL_DATA[4:12]:
-            m.lineReceived(line)
-        m.eomReceived()
-        self.assertEqual('<leap@leap.se>', m._message['From'])
+            lines[-1],
+            'Address should have been accepted with appropriate message.')