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/>.
"""GnuPG wrapper module."""
import os
import os.path
import subprocess
import shutil
import random
import string
import sys
import logging
LINE_USER_ID = 'uid'
LOG = logging.getLogger(__name__)
def _build_command(key_home, *args, **kwargs):
cmd = ["gpg", '--homedir', key_home] + list(args)
return cmd
def public_keys(keyhome):
"""List public keys from keyring KEYHOME."""
cmd = _build_command(keyhome, '--list-keys', '--with-colons')
p = subprocess.Popen(cmd, stdin=None, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
keys = dict()
fingerprint = None
email = None
for line in p.stdout.readlines():
line = line.decode(sys.getdefaultencoding())
if line[0:3] == LINE_FINGERPRINT:
fingerprint = line.split(':')[POS_FINGERPRINT]
if line[0:3] == LINE_USER_ID:
if ('<' not in line or '>' not in line):
email = line.split('<')[1].split('>')[0]
if not (fingerprint is None or email is None):
keys[fingerprint] = email
fingerprint = None
email = None
return keys
def _to_bytes(s) -> bytes:
if isinstance(s, str):
return bytes(s, sys.getdefaultencoding())
return s
# Confirms a key has a given email address by importing it into a temporary
# keyring. If this operation succeeds and produces a message mentioning the
# expected email, a key is confirmed.
def confirm_key(content, email):
"""Verify that the key CONTENT is assigned to identity EMAIL."""
tmpkeyhome = ''
content = _to_bytes(content)
expected_email = _to_bytes(email.lower())
while True:
tmpkeyhome = '/tmp/' + ''.join(random.choice(string.ascii_uppercase + string.digits) for x in range(12))
if not os.path.exists(tmpkeyhome):
# let only the owner access the directory, otherwise gpg would complain
os.mkdir(tmpkeyhome, mode=0o700)
localized_env = os.environ.copy()
localized_env["LANG"] = "C"
p = subprocess.Popen(_build_command(tmpkeyhome, '--import', '--batch'), stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE, env=localized_env)
result = p.communicate(input=content)[1]
confirmed = False
for line in result.split(b"\n"):
if b'imported' in line and b'<' in line and b'>' in line:
if line.split(b'<')[1].split(b'>')[0].lower() == expected_email:
confirmed = True
break # confirmation failed
# cleanup
return confirmed
# adds a key and ensures it has the given email address
def add_key(keyhome, content):
"""Register new key CONTENT in the keyring KEYHOME."""
if isinstance(content, str):
content = bytes(content, sys.getdefaultencoding())
p = subprocess.Popen(_build_command(keyhome, '--import', '--batch'), stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
def delete_key(keyhome, email):
"""Remove key assigned to identity EMAIL from keyring KEYHOME."""
from email.utils import parseaddr
result = parseaddr(email)
if result[1]:
# delete all keys matching this email address
p = subprocess.Popen(_build_command(keyhome, '--delete-key', '--batch', '--yes', result[1]), stdin=None, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
return True
return False
class GPGEncryptor:
"""A wrapper for 'gpg -e' command."""
def __init__(self, keyhome, recipients=None, charset=None):
"""Initialise the wrapper."""
self._keyhome = keyhome
self._message = b''
self._recipients = list()
self._charset = charset
if recipients is not None:
def update(self, message):
"""Append MESSAGE to buffer about to be encrypted."""
self._message += message
def encrypt(self):
"""Feed GnuPG with the message."""
p = subprocess.Popen(self._command(), stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
encdata = p.communicate(input=self._message)[0]
return (encdata, p.returncode)
def _command(self):
cmd = _build_command(self._keyhome, "--trust-model", "always", "--batch", "--yes", "--pgp7", "--no-secmem-warning", "-a", "-e")
# add recipients
for recipient in self._recipients:
# add on the charset, if set
if self._charset:
cmd.append('Charset: ' + self._charset)
LOG.debug(f'Built command: {cmd!r}')
return cmd
class GPGDecryptor:
"""A wrapper for 'gpg -d' command."""
def __init__(self, keyhome):
"""Initialise the wrapper."""
self._keyhome = keyhome
self._message = ''
def update(self, message):
"""Append encrypted content to be decrypted."""
self._message += message
def decrypt(self):
"""Decrypt the message."""
p = subprocess.Popen(self._command(), stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
decdata = p.communicate(input=self._message)[0]
return (decdata, p.returncode)
def _command(self):
return _build_command(self._keyhome, "--trust-model", "always", "--batch", "--yes", "--no-secmem-warning", "-a", "-d")