A mailgate for Postfix to encrypt incoming and outgoing email with S/MIME and/or OpenPGP and decrypting OpenPGP encrypted emails https://lacre.io
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# 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
# 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
import time
# imports for S/MIME
from M2Crypto import BIO, Rand, SMIME, X509
from email.mime.message import MIMEMessage
import logging
import lacre
import lacre.text as text
import lacre.config as conf
LOG = logging.getLogger(__name__)
def gpg_encrypt( raw_message, recipients ):
global LOG
if not conf.config_item_set('gpg', 'keyhome'):
LOG.error("No valid entry for gpg keyhome. Encryption aborted.")
return recipients
keys = GnuPG.public_keys( conf.get_item('gpg', 'keyhome') )
for fingerprint in keys:
keys[fingerprint] = sanitize_case_sense(keys[fingerprint])
# This list will be filled with pairs (M, N), where M is the destination
# address we're going to deliver the message to and N is the identity we're
# going to encrypt it for.
gpg_to = list()
ungpg_to = list()
enc_keymap_only = conf.config_item_equals('default', 'enc_keymap_only', 'yes')
for to in recipients:
# Check if recipient is in keymap
if conf.config_item_set('enc_keymap', to):
LOG.info("Encrypt keymap has key '%s'" % conf.get_item('enc_keymap', to) )
# Check we've got a matching key!
if conf.get_item('enc_keymap', to) in keys:
gpg_to.append( (to, conf.get_item('enc_keymap', to)) )
LOG.info("Key '%s' in encrypt keymap not found in keyring for email address '%s'." % (conf.get_item('enc_keymap', to), to))
# Check if key in keychain is present
if not enc_keymap_only:
if to in keys.values():
gpg_to.append( (to, to) )
# If this is an address with a delimiter (i.e. "foo+bar@example.com"),
# then strip whatever is found after the delimiter and try this address.
(newto, topic) = text.parse_delimiter(to)
if newto in keys.values():
gpg_to.append((to, newto))
# Check if there is a default key for the domain
splitted_to = to.split('@')
if len(splitted_to) > 1:
domain = splitted_to[1]
if conf.config_item_set('enc_domain_keymap', domain):
LOG.info("Encrypt domain keymap has key '%s'" % conf.get_item('enc_domain_keymap', domain) )
# Check we've got a matching key!
if conf.get_item('enc_domain_keymap', domain) in keys:
LOG.info("Using default domain key for recipient '%s'" % to)
gpg_to.append( (to, conf.get_item('enc_domain_keymap', domain)) )
LOG.info("Key '%s' in encrypt domain keymap not found in keyring for email address '%s'." % (conf.get_item('enc_domain_keymap', domain), to))
# At this point no key has been found
LOG.debug("Recipient (%s) not in PGP domain list for encrypting." % to)
if gpg_to:
LOG.info("Encrypting email to: %s" % ' '.join( x[0] for x in 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 conf.config_item_equals('pgp_style', rcpt[0], 'mime'):
elif conf.config_item_equals('pgp_style', rcpt[0], 'inline'):
# Log message only if an unknown style is defined
if conf.config_item_set('pgp_style', rcpt[0]):
LOG.debug("Style %s for recipient %s is not known. Use default as fallback." % (conf.get_item("pgp_style", rcpt[0]), rcpt[0]))
# If no style is in settings defined for recipient, use default from settings
if conf.config_item_equals('default', 'mime_conversion', 'yes'):
if gpg_to_smtp_mime:
# Encrypt mail with PGP/MIME
raw_message_mime = copy.deepcopy(raw_message)
if conf.config_item_equals('default', 'add_header', 'yes'):
raw_message_mime['X-GPG-Mailgate'] = 'Encrypted by GPG Mailgate'
if 'Content-Transfer-Encoding' in raw_message_mime:
raw_message_mime.replace_header('Content-Transfer-Encoding', '8BIT')
raw_message_mime['Content-Transfer-Encoding'] = '8BIT'
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:
# Encrypt mail with PGP/INLINE
raw_message_inline = copy.deepcopy(raw_message)
if conf.config_item_equals('default', 'add_header', 'yes'):
raw_message_inline['X-GPG-Mailgate'] = 'Encrypted by GPG Mailgate'
if 'Content-Transfer-Encoding' in raw_message_inline:
raw_message_inline.replace_header('Content-Transfer-Encoding', '8BIT')
raw_message_inline['Content-Transfer-Encoding'] = '8BIT'
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 isinstance(message.get_payload(), str):
return encrypt_payload( message, gpg_to_cmdline ).get_payload()
for payload in message.get_payload():
if( isinstance(payload.get_payload(), list) ):
encrypted_payloads.extend( encrypt_all_payloads_inline( payload, gpg_to_cmdline ) )
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.
pgp_ver_part = email.message.Message()
pgp_ver_part.set_payload("Version: 1"+text.EOL)
pgp_ver_part.set_param('PGP/MIME version identification', "", 'Content-Description' )
encrypted_part = email.message.Message()
encrypted_part.set_param('name', "encrypted.asc")
encrypted_part.set_param('OpenPGP encrypted message', "", 'Content-Description' )
encrypted_part.set_param('inline', "", 'Content-Disposition' )
encrypted_part.set_param('filename', "encrypted.asc", 'Content-Disposition' )
if isinstance(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.
encoding = sys.getdefaultencoding()
if 'Content-Type' in message and not message['Content-Type'].startswith('multipart'):
additionalSubHeader="Content-Type: "+message['Content-Type']+text.EOL
(base, encoding) = text.parse_content_type(message['Content-Type'])
LOG.debug(f"Identified encoding as {encoding}")
encrypted_part.set_payload(additionalSubHeader+text.EOL +message.get_payload(decode=True).decode(encoding))
check_nested = True
processed_payloads = generate_message_from_payloads(message)
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 'Content-Type' in message:
message.replace_header('Content-Type', f"multipart/encrypted; protocol=\"application/pgp-encrypted\"; boundary=\"{boundary}\""+text.EOL)
message['Content-Type'] = f"multipart/encrypted; protocol=\"application/pgp-encrypted\"; boundary=\"{boundary}\""+text.EOL
return [ pgp_ver_part, encrypt_payload(encrypted_part, gpg_to_cmdline, check_nested) ]
def encrypt_payload( payload, gpg_to_cmdline, check_nested = True ):
global LOG
raw_payload = payload.get_payload(decode=True)
if check_nested and text.is_pgp_inline(raw_payload):
LOG.debug("Message is already pgp encrypted. No nested encryption needed.")
return payload
# No check is needed for conf.get_item('gpg', 'keyhome') as this is already done in method gpg_encrypt
gpg = GnuPG.GPGEncryptor( conf.get_item('gpg', 'keyhome'), gpg_to_cmdline, payload.get_content_charset() )
gpg.update( raw_payload )
encrypted_data, returncode = gpg.encrypt()
LOG.debug("Return code from encryption=%d (0 indicates success)." % returncode)
if returncode != 0:
LOG.info("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 smime_encrypt( raw_message, recipients ):
global LOG
global from_addr
if not conf.config_item_set('smime', 'cert_path'):
LOG.info("No valid path for S/MIME certs found in config file. S/MIME encryption aborted.")
return recipients
cert_path = conf.get_item('smime', 'cert_path')+"/"
sk = X509.X509_Stack()
smime_to = list()
unsmime_to = list()
for addr in recipients:
cert_and_email = get_cert_for_email(addr, cert_path)
if not (cert_and_email is None):
(to_cert, normal_email) = cert_and_email
LOG.debug("Found cert " + to_cert + " for " + addr + ": " + normal_email)
x509 = X509.load_cert(to_cert, format=X509.FORMAT_PEM)
if smime_to:
p7 = s.encrypt( BIO.MemoryBuffer( raw_message.as_string() ) )
# Output p7 in mail-friendly format.
out = BIO.MemoryBuffer()
out.write('From: ' + from_addr + text.EOL)
out.write('To: ' + raw_message['To'] + text.EOL)
if raw_message['Cc']:
out.write('Cc: ' + raw_message['Cc'] + text.EOL)
if raw_message['Bcc']:
out.write('Bcc: ' + raw_message['Bcc'] + text.EOL)
if raw_message['Subject']:
out.write('Subject: '+ raw_message['Subject'] + text.EOL)
if conf.config_item_equals('default', 'add_header', 'yes'):
out.write('X-GPG-Mailgate: Encrypted by GPG Mailgate' + text.EOL)
s.write(out, p7)
LOG.debug(f"Sending message from {from_addr} to {smime_to}")
send_msg(out.read(), smime_to)
if unsmime_to:
LOG.debug(f"Unable to find valid S/MIME certificates for {unsmime_to}")
return unsmime_to
def get_cert_for_email( to_addr, cert_path ):
global LOG
insensitive = conf.config_item_equals('default', 'mail_case_insensitive', 'yes')
files_in_directory = os.listdir(cert_path)
for filename in files_in_directory:
file_path = os.path.join(cert_path, filename)
if not os.path.isfile(file_path):
if insensitive:
if filename.casefold() == to_addr:
return (file_path, to_addr)
if filename == to_addr:
return (file_path, to_addr)
# support foo+ignore@bar.com -> foo@bar.com
(fixed_up_email, topic) = text.parse_delimiter(to_addr)
if topic is None:
# delimiter not used
return None
LOG.debug(f"Looking up certificate for {fixed_up_email} after parsing {to_addr}")
return get_cert_for_email(fixed_up_email, cert_path)
def sanitize_case_sense( address ):
if conf.config_item_equals('default', 'mail_case_insensitive', 'yes'):
address = address.lower()
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( isinstance(payload.get_payload(), list) ):
return message
def get_first_payload( payloads ):
if payloads.is_multipart():
return get_first_payload(payloads.get_payload(0))
return payloads
def send_msg( message, recipients ):
global LOG
global from_addr
recipients = [_f for _f in recipients if _f]
if recipients:
LOG.info(f"Sending email to: {recipients!r}")
relay = (conf.get_item('relay', 'host'), int(conf.get_item('relay', 'port')))
smtp = smtplib.SMTP(relay[0], relay[1])
if conf.config_item_equals('relay', 'starttls', 'yes'):
smtp.sendmail( from_addr, recipients, message )
LOG.info("No recipient found")
def deliver_message( raw_message, from_address, to_addrs ):
global LOG
global from_addr
# Ugly workaround to keep the code working without too many changes.
from_addr = from_address
recipients_left = [sanitize_case_sense(recipient) for recipient in to_addrs]
# There is no need for nested encryption
first_payload = get_first_payload(raw_message)
if first_payload.get_content_type() == 'application/pkcs7-mime':
LOG.debug("Message is already encrypted with S/MIME. Encryption aborted.")
send_msg(raw_message.as_string(), recipients_left)
first_payload = first_payload.get_payload(decode=True)
if text.is_pgp_inline(first_payload):
LOG.debug("Message is already encrypted as PGP/INLINE. Encryption aborted.")
send_msg(raw_message.as_string(), recipients_left)
if raw_message.get_content_type() == 'multipart/encrypted':
LOG.debug("Message is already encrypted. Encryption aborted.")
send_msg(raw_message.as_string(), recipients_left)
# Encrypt mails for recipients with known public PGP keys
recipients_left = gpg_encrypt(raw_message, recipients_left)
if not recipients_left:
# Encrypt mails for recipients with known S/MIME certificate
recipients_left = smime_encrypt(raw_message, recipients_left)
if not recipients_left:
# Send out mail to recipients which are left
send_msg(raw_message.as_string(), recipients_left)
def exec_time_info(start_timestamp):
elapsed_s = time.time() - start_timestamp
process_t = time.process_time()
return (elapsed_s, process_t)