gpg-mailgate.py

#!/usr/bin/python

#
#	gpg-mailgate
#
#	This file is part of the gpg-mailgate source code.
#
#	gpg-mailgate 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.
#
#	gpg-mailgate source code 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 gpg-mailgate source code. If not, see <http://www.gnu.org/licenses/>.
#

from ConfigParser import RawConfigParser
from email.mime.base import MIMEBase
from email.mime.multipart import MIMEMultipart
import copy
import email
import email.message
import email.utils
import GnuPG
import os
import re
import smtplib
import sys
import syslog
import traceback


# Read configuration from /etc/gpg-mailgate.conf
_cfg = RawConfigParser()
_cfg.read('/etc/gpg-mailgate.conf')
cfg = dict()
for sect in _cfg.sections():
	cfg[sect] = dict()
	for (name, value) in _cfg.items(sect):
		cfg[sect][name] = value


def log( msg ):
	if 'logging' in cfg and 'file' in cfg['logging']:
		if cfg['logging'].get('file') == "syslog":
			syslog.syslog(syslog.LOG_INFO | syslog.LOG_MAIL, msg)
		else:
			logfile = open(cfg['logging']['file'], 'a')
			logfile.write(msg + "\n")
			logfile.close()

verbose = 'logging' in cfg and 'verbose' in cfg['logging'] and cfg['logging'].get('verbose') == 'yes'

# Read e-mail from stdin
raw = sys.stdin.read()
raw_message = email.message_from_string( raw )
from_addr = raw_message['From']
to_addrs = sys.argv[1:]


def gpg_encrypt( raw_message, recipients ):

	if not get_bool_from_cfg('gpg', 'keyhome'):
		log("No valid entry for gpg keyhome. Encryption aborted.")
		return recipients

	keys = GnuPG.public_keys( cfg['gpg']['keyhome'] )
	for fingerprint in keys:
		keys[fingerprint] = sanitize_case_sense(keys[fingerprint])

	gpg_to = list()
	ungpg_to = list()

	for to in recipients:

		# Check if key in keychain is present
		if to in keys.values():
			gpg_to.append( (to, to) )
			continue

		# At this point no key has been found
		if verbose:
			log("Recipient (%s) not in PGP domain list for encrypting." % to)
		ungpg_to.append(to)

	if gpg_to != list():
		log("Encrypting email to: %s" % ' '.join( map(lambda x: x[0], gpg_to) ))

		# Getting PGP style for recipient
		gpg_to_smtp_mime = list()
		gpg_to_cmdline_mime = list()

		gpg_to_smtp_inline = list()
		gpg_to_cmdline_inline = list()

		for rcpt in gpg_to:
			# Checking pre defined styles in settings first
			if get_bool_from_cfg('pgp_style', rcpt[0], 'mime'):
				gpg_to_smtp_mime.append(rcpt[0])
				gpg_to_cmdline_mime.extend(rcpt[1].split(','))
			elif get_bool_from_cfg('pgp_style', rcpt[0], 'inline'):
				gpg_to_smtp_inline.append(rcpt[0])
				gpg_to_cmdline_inline.extend(rcpt[1].split(','))
			else:
				# Log message only if an unknown style is defined
				if get_bool_from_cfg('pgp_style', rcpt[0]):
					log("Style %s for recipient %s is not known. Use default as fallback." % (cfg['pgp_style'][rcpt[0]], rcpt[0]))

				# If no style is in settings defined for recipient, use default from settings
				if get_bool_from_cfg('default', 'mime_conversion', 'yes'):
					gpg_to_smtp_mime.append(rcpt[0])
					gpg_to_cmdline_mime.extend(rcpt[1].split(','))
				else:
					gpg_to_smtp_inline.append(rcpt[0])
					gpg_to_cmdline_inline.extend(rcpt[1].split(','))

		if gpg_to_smtp_mime != list():
			# Encrypt mail with PGP/MIME
			raw_message_mime = copy.deepcopy(raw_message)

			if get_bool_from_cfg('default', 'add_header', 'yes'):
				raw_message_mime['X-GPG-Mailgate'] = 'Encrypted by GPG Mailgate'

			encrypted_payloads = encrypt_all_payloads_mime( raw_message_mime, gpg_to_cmdline_mime )
			raw_message_mime.set_payload( encrypted_payloads )

			send_msg( raw_message_mime.as_string(), gpg_to_smtp_mime )

		if gpg_to_smtp_inline != list():
			# Encrypt mail with PGP/INLINE
			raw_message_inline = copy.deepcopy(raw_message)

			if get_bool_from_cfg('default', 'add_header', 'yes'):
				raw_message_inline['X-GPG-Mailgate'] = 'Encrypted by GPG Mailgate'

			encrypted_payloads = encrypt_all_payloads_inline( raw_message_inline, gpg_to_cmdline_inline )
			raw_message_inline.set_payload( encrypted_payloads )

			send_msg( raw_message_inline.as_string(), gpg_to_smtp_inline )

	return ungpg_to


def encrypt_all_payloads_inline( message, gpg_to_cmdline ):

	# This breaks cascaded MIME messages. Blame PGP/INLINE.
	encrypted_payloads = list()
	if type( message.get_payload() ) == str:
		return encrypt_payload( message, gpg_to_cmdline ).get_payload()

	for payload in message.get_payload():
		if( type( payload.get_payload() ) == list ):
			encrypted_payloads.extend( encrypt_all_payloads_inline( payload, gpg_to_cmdline ) )
		else:
			encrypted_payloads.append( encrypt_payload( payload, gpg_to_cmdline ) )

	return encrypted_payloads


def encrypt_all_payloads_mime( message, gpg_to_cmdline ):

	# Convert a plain text email into PGP/MIME attachment style.  Modeled after enigmail.
	submsg1 = email.message.Message()
	submsg1.set_payload("Version: 1\n")
	submsg1.set_type("application/pgp-encrypted")
	submsg1.set_param('PGP/MIME version identification', "", 'Content-Description' )

	submsg2 = email.message.Message()
	submsg2.set_type("application/octet-stream")
	submsg2.set_param('name', "encrypted.asc")
	submsg2.set_param('OpenPGP encrypted message', "", 'Content-Description' )
	submsg2.set_param('inline', "",                'Content-Disposition' )
	submsg2.set_param('filename', "encrypted.asc", 'Content-Disposition' )

	if type ( message.get_payload() ) == str:
		# WTF!  It seems to swallow the first line.  Not sure why.  Perhaps
		# it's skipping an imaginary blank line someplace. (ie skipping a header)
		# Workaround it here by prepending a blank line.
		# This happens only on text only messages.
		submsg2.set_payload("\n" + message.get_payload())
		check_nested = True
	else:
		processed_payloads = generate_message_from_payloads(message)
		submsg2.set_payload(processed_payloads.as_string())
		check_nested = False

	message.preamble = "This is an OpenPGP/MIME encrypted message (RFC 2440 and 3156)"

	# Use this just to generate a MIME boundary string.
	junk_msg = MIMEMultipart()
	junk_str = junk_msg.as_string()  # WTF!  Without this, get_boundary() will return 'None'!
	boundary = junk_msg.get_boundary()

    # This also modifies the boundary in the body of the message, ie it gets parsed.
	if message.has_key('Content-Type'):
		message.replace_header('Content-Type', "multipart/encrypted; protocol=\"application/pgp-encrypted\";\nboundary=\"%s\"\n" % boundary)
	else:
		message['Content-Type'] = "multipart/encrypted; protocol=\"application/pgp-encrypted\";\nboundary=\"%s\"\n" % boundary

	return [ submsg1, encrypt_payload(submsg2, gpg_to_cmdline, check_nested) ]


def encrypt_payload( payload, gpg_to_cmdline, check_nested = True ):

	raw_payload = payload.get_payload(decode=True)
	if check_nested and "-----BEGIN PGP MESSAGE-----" in raw_payload and "-----END PGP MESSAGE-----" in raw_payload:
		if verbose:
			log("Message is already pgp encrypted. No nested encryption needed.")
		return payload

	# No check is needed for cfg['gpg']['keyhome'] as this is already done in method gpg_encrypt
	gpg = GnuPG.GPGEncryptor( cfg['gpg']['keyhome'], gpg_to_cmdline, payload.get_content_charset() )
	gpg.update( raw_payload )
	encrypted_data, returncode = gpg.encrypt()
	if verbose:
		log("Return code from encryption=%d (0 indicates success)." % returncode)
	if returncode != 0:
		log("Encrytion failed with return code %d. Encryption aborted." % returncode)
		return payload

	payload.set_payload( encrypted_data )
	isAttachment = payload.get_param( 'attachment', None, 'Content-Disposition' ) is not None

	if isAttachment:
		filename = payload.get_filename()
		if filename:
			pgpFilename = filename + ".pgp"
			if not (payload.get('Content-Disposition') is None):
				payload.set_param( 'filename', pgpFilename, 'Content-Disposition' )
			if not (payload.get('Content-Type') is None) and not (payload.get_param( 'name' ) is None):
				payload.set_param( 'name', pgpFilename )
	if not (payload.get('Content-Transfer-Encoding') is None):
		payload.replace_header( 'Content-Transfer-Encoding', "7bit" )

	return payload


def get_bool_from_cfg( section, key = None, evaluation = None ):

	if not (key is None) and not (evaluation is None):
		return section in cfg and cfg[section].get(key) == evaluation

	elif not (key is None) and (evaluation is None):
		return section in cfg and not (cfg[section].get(key) is None)

	else:
		return section in cfg

def sanitize_case_sense( address ):

	if get_bool_from_cfg('default', 'mail_case_insensitive', 'yes'):
		address = address.lower()
	else:
		splitted_address = address.split('@')
		if len(splitted_address) > 1:
			address = splitted_address[0] + '@' + splitted_address[1].lower()

	return address

def generate_message_from_payloads( payloads, message = None ):

	if message == None:
		message = email.mime.multipart.MIMEMultipart(payloads.get_content_subtype())

	for payload in payloads.get_payload():
		if( type( payload.get_payload() ) == list ):
			message.attach(generate_message_from_payloads(payload))
		else:
			message.attach(payload)

	return message

def get_first_payload( payloads ):

	if payloads.is_multipart():
		return get_first_payload(payloads.get_payload(0))
	else:
		return payloads

def send_msg( message, recipients ):

	recipients = filter(None, recipients)
	if recipients:
		if not (get_bool_from_cfg('relay', 'host') and get_bool_from_cfg('relay', 'port')):
			log("Missing settings for relay. Sending email aborted.")
			return None
		log("Sending email to: <%s>" % '> <'.join( recipients ))
		relay = (cfg['relay']['host'], int(cfg['relay']['port']))
		smtp = smtplib.SMTP(relay[0], relay[1])
		smtp.sendmail( from_addr, recipients, message )
	else:
		log("No recipient found")

def sort_recipients( raw_message, from_addr, to_addrs ):

	recipients_left = list()
	for recipient in to_addrs:
		recipients_left.append(sanitize_case_sense(recipient))

	# There is no need for nested encryption
	first_payload = get_first_payload(raw_message)
	if first_payload.get_content_type() == 'application/pkcs7-mime':
		if verbose:
			log("Message is already encrypted with S/MIME. Encryption aborted.")
		send_msg(raw_message.as_string(), recipients_left)
		return

	first_payload = first_payload.get_payload(decode=True)
	if "-----BEGIN PGP MESSAGE-----" in first_payload and "-----END PGP MESSAGE-----" in first_payload:
		if verbose:
			log("Message is already encrypted as PGP/INLINE. Encryption aborted.")
		send_msg(raw_message.as_string(), recipients_left)
		return

	if raw_message.get_content_type() == 'multipart/encrypted':
		if verbose:
			log("Message is already encrypted. Encryption aborted.")
		send_msg(raw_message.as_string(), recipients_left)
		return

	# Encrypt mails for recipients with known public PGP keys
	recipients_left = gpg_encrypt(raw_message, recipients_left)
	if recipients_left == list():
		return

	# Send out mail to recipients which are left
	send_msg(raw_message.as_string(), recipients_left)


# Let's start
sort_recipients(raw_message, from_addr, to_addrs)