Make SMTP relay RFC 3156 compliant.

1 files changed, 379 insertions, 0 deletions

diff --git a/src/leap/mail/smtp/rfc3156.py b/src/leap/mail/smtp/rfc3156.py
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+++ b/src/leap/mail/smtp/rfc3156.py
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+# -*- coding: utf-8 -*-
+# rfc3156.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/>.
+
+"""
+Implements RFC 3156: MIME Security with OpenPGP.
+"""
+
+import re
+import base64
+from abc import ABCMeta, abstractmethod
+from StringIO import StringIO
+
+from email.mime.application import MIMEApplication
+from email.mime.multipart import MIMEMultipart
+from email import errors
+from email.generator import (
+    Generator,
+    fcre,
+    NL,
+    _make_boundary,
+)
+
+
+#
+# A generator that solves http://bugs.python.org/issue14983
+#
+
+class RFC3156CompliantGenerator(Generator):
+    """
+    An email generator that addresses Python's issue #14983 for multipart
+    messages.
+
+    This is just a copy of email.generator.Generator which fixes the following
+    bug: http://bugs.python.org/issue14983
+    """
+
+    def _handle_multipart(self, msg):
+        """
+        A multipart handling implementation that addresses issue #14983.
+
+        This is just a copy of the parent's method which fixes the following
+        bug: http://bugs.python.org/issue14983 (see the line marked with
+        "(***)").
+
+        :param msg: The multipart message to be handled.
+        :type msg: email.message.Message
+        """
+        # The trick here is to write out each part separately, merge them all
+        # together, and then make sure that the boundary we've chosen isn't
+        # present in the payload.
+        msgtexts = []
+        subparts = msg.get_payload()
+        if subparts is None:
+            subparts = []
+        elif isinstance(subparts, basestring):
+            # e.g. a non-strict parse of a message with no starting boundary.
+            self._fp.write(subparts)
+            return
+        elif not isinstance(subparts, list):
+            # Scalar payload
+            subparts = [subparts]
+        for part in subparts:
+            s = StringIO()
+            g = self.clone(s)
+            g.flatten(part, unixfrom=False)
+            msgtexts.append(s.getvalue())
+        # BAW: What about boundaries that are wrapped in double-quotes?
+        boundary = msg.get_boundary()
+        if not boundary:
+            # Create a boundary that doesn't appear in any of the
+            # message texts.
+            alltext = NL.join(msgtexts)
+            boundary = _make_boundary(alltext)
+            msg.set_boundary(boundary)
+        # If there's a preamble, write it out, with a trailing CRLF
+        if msg.preamble is not None:
+            preamble = msg.preamble
+            if self._mangle_from_:
+                preamble = fcre.sub('>From ', msg.preamble)
+            self._fp.write(preamble + '\n')
+        # dash-boundary transport-padding CRLF
+        self._fp.write('--' + boundary + '\n')
+        # body-part
+        if msgtexts:
+            self._fp.write(msgtexts.pop(0))
+        # *encapsulation
+        # --> delimiter transport-padding
+        # --> CRLF body-part
+        for body_part in msgtexts:
+            # delimiter transport-padding CRLF
+            self._fp.write('\n--' + boundary + '\n')
+            # body-part
+            self._fp.write(body_part)
+        # close-delimiter transport-padding
+        self._fp.write('\n--' + boundary + '--' + '\n')  # (***) Solve #14983
+        if msg.epilogue is not None:
+            self._fp.write('\n')
+            epilogue = msg.epilogue
+            if self._mangle_from_:
+                epilogue = fcre.sub('>From ', msg.epilogue)
+            self._fp.write(epilogue)
+
+
+#
+# Base64 encoding: these are almost the same as python's email.encoder
+# solution, but a bit modified.
+#
+
+def _bencode(s):
+    """
+    Encode C{s} in base64.
+
+    :param s: The string to be encoded.
+    :type s: str
+    """
+    # We can't quite use base64.encodestring() since it tacks on a "courtesy
+    # newline".  Blech!
+    if not s:
+        return s
+    value = base64.encodestring(s)
+    return value[:-1]
+
+
+def encode_base64(msg):
+    """
+    Encode a non-multipart message's payload in Base64 (in place).
+
+    This method modifies the message contents in place and adds or replaces an
+    appropriate Content-Transfer-Encoding header.
+
+    :param msg: The non-multipart message to be encoded.
+    :type msg: email.message.Message
+    """
+    orig = msg.get_payload()
+    encdata = _bencode(orig)
+    msg.set_payload(encdata)
+    # replace or set the Content-Transfer-Encoding header.
+    try:
+        msg.replace_header('Content-Transfer-Encoding', 'base64')
+    except KeyError:
+        msg['Content-Transfer-Encoding'] = 'base64'
+
+
+def encode_base64_rec(msg):
+    """
+    Encode (possibly multipart) messages in base64 (in place).
+
+    This method modifies the message contents in place.
+
+    :param msg: The non-multipart message to be encoded.
+    :type msg: email.message.Message
+    """
+    if not msg.is_multipart():
+        encode_base64(msg)
+    else:
+        for sub in msg.get_payload():
+            encode_base64_rec(sub)
+
+
+#
+# RFC 1847: multipart/signed and multipart/encrypted
+#
+
+class MultipartSigned(MIMEMultipart):
+    """
+    Multipart/Signed MIME message according to RFC 1847.
+
+    2.1. Definition of Multipart/Signed
+
+      (1)  MIME type name: multipart
+      (2)  MIME subtype name: signed
+      (3)  Required parameters: boundary, protocol, and micalg
+      (4)  Optional parameters: none
+      (5)  Security considerations: Must be treated as opaque while in
+           transit
+
+    The multipart/signed content type contains exactly two body parts.
+    The first body part is the body part over which the digital signature
+    was created, including its MIME headers.  The second body part
+    contains the control information necessary to verify the digital
+    signature.  The first body part may contain any valid MIME content
+    type, labeled accordingly.  The second body part is labeled according
+    to the value of the protocol parameter.
+
+    When the OpenPGP digital signature is generated:
+
+    (1)   The data to be signed MUST first be converted to its content-
+          type specific canonical form.  For text/plain, this means
+          conversion to an appropriate character set and conversion of
+          line endings to the canonical <CR><LF> sequence.
+
+    (2)   An appropriate Content-Transfer-Encoding is then applied; see
+          section 3.  In particular, line endings in the encoded data
+          MUST use the canonical <CR><LF> sequence where appropriate
+          (note that the canonical line ending may or may not be present
+          on the last line of encoded data and MUST NOT be included in
+          the signature if absent).
+
+    (3)   MIME content headers are then added to the body, each ending
+          with the canonical <CR><LF> sequence.
+
+    (4)   As described in section 3 of this document, any trailing
+          whitespace MUST then be removed from the signed material.
+
+    (5)   As described in [2], the digital signature MUST be calculated
+          over both the data to be signed and its set of content headers.
+
+    (6)   The signature MUST be generated detached from the signed data
+          so that the process does not alter the signed data in any way.
+    """
+
+    def __init__(self, protocol, micalg, boundary=None, _subparts=None):
+        """
+        Initialize the multipart/signed message.
+
+        :param boundary: the multipart boundary string. By default it is
+            calculated as needed.
+        :type boundary: str
+        :param _subparts: a sequence of initial subparts for the payload. It
+            must be an iterable object, such as a list. You can always
+            attach new subparts to the message by using the attach() method.
+        :type _subparts: iterable
+        """
+        MIMEMultipart.__init__(
+            self, _subtype='signed', boundary=boundary,
+            _subparts=_subparts)
+        self.set_param('protocol', protocol)
+        self.set_param('micalg', micalg)
+
+    def attach(self, payload):
+        """
+        Add the C{payload} to the current payload list.
+
+        Also prevent from adding payloads with wrong Content-Type and from
+        exceeding a maximum of 2 payloads.
+
+        :param payload: The payload to be attached.
+        :type payload: email.message.Message
+        """
+        # second payload's content type must be equal to the protocol
+        # parameter given on object creation
+        if len(self.get_payload()) == 1:
+            if payload.get_content_type() != self.get_param('protocol'):
+                raise errors.MultipartConversionError(
+                    'Wrong content type %s.' % payload.get_content_type)
+        # prevent from adding more payloads
+        if len(self._payload) == 2:
+            raise errors.MultipartConversionError(
+                'Cannot have more than two subparts.')
+        MIMEMultipart.attach(self, payload)
+
+
+class MultipartEncrypted(MIMEMultipart):
+    """
+    Multipart/encrypted MIME message according to RFC 1847.
+
+    2.2. Definition of Multipart/Encrypted
+
+      (1)  MIME type name: multipart
+      (2)  MIME subtype name: encrypted
+      (3)  Required parameters: boundary, protocol
+      (4)  Optional parameters: none
+      (5)  Security considerations: none
+
+    The multipart/encrypted content type contains exactly two body parts.
+    The first body part contains the control information necessary to
+    decrypt the data in the second body part and is labeled according to
+    the value of the protocol parameter.  The second body part contains
+    the data which was encrypted and is always labeled
+    application/octet-stream.
+    """
+
+    def __init__(self, protocol, boundary=None, _subparts=None):
+        """
+        :param protocol: The encryption protocol to be added as a parameter to
+            the Content-Type header.
+        :type protocol: str
+        :param boundary: the multipart boundary string. By default it is
+            calculated as needed.
+        :type boundary: str
+        :param _subparts: a sequence of initial subparts for the payload. It
+            must be an iterable object, such as a list. You can always
+            attach new subparts to the message by using the attach() method.
+        :type _subparts: iterable
+        """
+        MIMEMultipart.__init__(
+            self, _subtype='encrypted', boundary=boundary,
+            _subparts=_subparts)
+        self.set_param('protocol', protocol)
+
+    def attach(self, payload):
+        """
+        Add the C{payload} to the current payload list.
+
+        Also prevent from adding payloads with wrong Content-Type and from
+        exceeding a maximum of 2 payloads.
+
+        :param payload: The payload to be attached.
+        :type payload: email.message.Message
+        """
+        # first payload's content type must be equal to the protocol parameter
+        # given on object creation
+        if len(self._payload) == 0:
+            if payload.get_content_type() != self.get_param('protocol'):
+                raise errors.MultipartConversionError(
+                    'Wrong content type.')
+        # second payload is always application/octet-stream
+        if len(self._payload) == 1:
+            if payload.get_content_type() != 'application/octet-stream':
+                raise errors.MultipartConversionError(
+                    'Wrong content type %s.' % payload.get_content_type)
+        # prevent from adding more payloads
+        if len(self._payload) == 2:
+            raise errors.MultipartConversionError(
+                'Cannot have more than two subparts.')
+        MIMEMultipart.attach(self, payload)
+
+
+#
+# RFC 3156: application/pgp-encrypted, application/pgp-signed and
+# application-pgp-signature.
+#
+
+class PGPEncrypted(MIMEApplication):
+    """
+    Application/pgp-encrypted MIME media type according to RFC 3156.
+
+      * MIME media type name: application
+      * MIME subtype name: pgp-encrypted
+      * Required parameters: none
+      * Optional parameters: none
+    """
+
+    def __init__(self, version=1):
+        data = "Version: %d" % version
+        MIMEApplication.__init__(self, data, 'pgp-encrypted')
+
+
+class PGPSignature(MIMEApplication):
+    """
+    Application/pgp-signature MIME media type according to RFC 3156.
+
+      * MIME media type name: application
+      * MIME subtype name: pgp-signature
+      * Required parameters: none
+      * Optional parameters: none
+    """
+    def __init__(self, _data, name='signature.asc'):
+        MIMEApplication.__init__(self, _data, 'pgp-signature',
+            _encoder=lambda x: x, name=name)
+        self.add_header('Content-Description', 'OpenPGP Digital Signature')
+
+
+class PGPKeys(MIMEApplication):
+    """
+    Application/pgp-keys MIME media type according to RFC 3156.
+
+      * MIME media type name: application
+      * MIME subtype name: pgp-keys
+      * Required parameters: none
+      * Optional parameters: none
+    """
+
+    def __init__(self, _data):
+        MIMEApplication.__init__(self, _data, 'pgp-keys')