diff options
| -rw-r--r-- | .gitignore | 2 | ||||
| -rw-r--r-- | config.py.dist | 16 | ||||
| -rw-r--r-- | key_loader.py | 38 | ||||
| -rw-r--r-- | main.py | 85 | ||||
| -rw-r--r-- | pgp-milter.service | 16 | ||||
| -rw-r--r-- | utils.py | 100 |
6 files changed, 257 insertions, 0 deletions
diff --git a/.gitignore b/.gitignore new file mode 100644 index 0000000..382ddaa --- /dev/null +++ b/.gitignore @@ -0,0 +1,2 @@ +__pycache__/ +config.py diff --git a/config.py.dist b/config.py.dist new file mode 100644 index 0000000..e35e8ae --- /dev/null +++ b/config.py.dist @@ -0,0 +1,16 @@ +socket = '/var/spool/postfix/pgp-milter/pgp-milter.sock' +db_config = { + 'host': 'localhost', + 'user': 'user', + 'password': 'password', + 'database': 'database' +} + +# Things to bear in mind when writing this query: +# - `fingerprint` can be any deduplicating attribute of any type +# - `raw_data` can either be armored or unarmored key data +# - column names don't matter +# - the input argument (%s) is a series of addresses, like so: +# - `'a@example.com', 'b@example.com', 'c@example.com'` +# - a prepared statement is used so input is sanitized for you +key_loader_query = 'SELECT fingerprint, raw_data FROM pgp_keys WHERE addr IN (%s)' diff --git a/key_loader.py b/key_loader.py new file mode 100644 index 0000000..4867d07 --- /dev/null +++ b/key_loader.py @@ -0,0 +1,38 @@ +import config +import mysql.connector as mysql +import pgpy + +def load_keys(addrs: list[str]) -> list[pgpy.PGPKey]: + if len(addrs) < 1: + return [] + + db = mysql.connect(**config.db_config) + try: + stmt = db.cursor() + except Exception as e: + db.close() + raise e + + try: + stmt.execute(\ + format_multiquery(config.key_loader_query, len(addrs)), \ + tuple(addrs) \ + ) + + keys = {} + for (keyfpr, keydata) in stmt: + if keyfpr in keys: + continue + key = pgpy.PGPKey() + try: + key.parse(keydata) + except: + continue + + return list(keys.values()) + finally: + stmt.close() + db.close() + +def format_multiquery(query: str, n_items: int) -> str: + return query % (', '.join(['%s'] * n_items),) @@ -0,0 +1,85 @@ +import config +import utils +import Milter +import email + +class PGPMilter(Milter.Base): + def __init__(self): + self.recipients = [] + self.headers = [] + self.content = bytes() + + @Milter.noreply + def connect(_self, _ip_name, _family, _hostaddr): + return Milter.CONTINUE + + @Milter.noreply + def envfrom(self, name, *esmtp_params): + self.__init__() + return Milter.CONTINUE + + @Milter.noreply + def envrcpt(self, name, *strings): + self.recipients.append(name) + return Milter.CONTINUE + + @Milter.noreply + def header(self, k: str, v: str): + self.headers.append((k.encode(), v.encode())) + return Milter.CONTINUE + + def eoh(self): + return Milter.CONTINUE + + def body(self, chunk): + self.content += chunk + return Milter.CONTINUE + + def eom(self): + raw_headers = b'\n'.join(map(lambda header : b'%s: %s' % header, self.headers)) + msg = email.message_from_bytes(raw_headers + b'\n\n' + self.content,\ + policy=email.policy.default) + + if b'-----BEGIN PGP MESSAGE-----' in self.content or utils.already_encrypted(msg): + return Milter.ACCEPT + + # TODO: remove debug print + print('Encrypting message to recipients: [%s]' % ', '.join(self.recipients)) + enc_msg, encrypted = utils.encrypt(msg, self.recipients) + if not encrypted: + # TODO: remove debug print + print('No keys found, passing through.') + return Milter.ACCEPT + + # `Content-Transfer-Encoding: quoted-printable` + # can prevent the message from being decrypted by clients + self.set_header(msg, 'Content-Transfer-Encoding', '') + for (k, v) in enc_msg.items(): + self.set_header(msg, k, v) + + enc_bytes = enc_msg.as_bytes() + enc_body = enc_bytes[enc_bytes.find(b'\n\n')+2:] + self.replacebody(enc_body) + + return Milter.ACCEPT + + def close(self): + self.__init__() + return Milter.CONTINUE + + def set_header(self, old_msg, k, v): + old_headers = old_msg.get_all(k) + if old_headers != None: + for i in range(len(old_headers)-1, -1, -1): + self.chgheader(k, i, '') + if v != None and len(v) > 0: + self.addheader(k, v) + +def main(): + Milter.factory = PGPMilter + Milter.set_flags(Milter.ADDHDRS + Milter.CHGHDRS + Milter.CHGBODY) + Milter.runmilter('cmail-pgp-milter', config.socket) + +if __name__ == '__main__': + print('Starting CMail PGP Milter') + main() diff --git a/pgp-milter.service b/pgp-milter.service new file mode 100644 index 0000000..2b93f40 --- /dev/null +++ b/pgp-milter.service @@ -0,0 +1,16 @@ +[Unit] +Description=CMail PGP Milter Service +Documentation=https://github.com/cflems/pgp-milter +After=network.target + +[Service] +Type=exec +User=pgp-milter +Group=pgp-milter +StandardOutput=append:/var/log/pgp-milter.log +StandardError=append:/var/log/pgp-milter.err +ExecStart=/usr/bin/python3 /opt/pgp-milter/main.py +Restart=on-failure + +[Install] +WantedBy=multi-user.target diff --git a/utils.py b/utils.py new file mode 100644 index 0000000..f4c4f9a --- /dev/null +++ b/utils.py @@ -0,0 +1,100 @@ +import key_loader +import pgpy +import email +from email.message import EmailMessage +from email.mime.multipart import MIMEMultipart +from email.mime.application import MIMEApplication +from email.mime.text import MIMEText +from copy import deepcopy +from random import choices as alphabet_random +from string import ascii_letters, digits + +protected_headers = ['to', 'cc', 'from', 'reply-to', 'followup-to', 'subject', 'date',\ + 'message-id'] +structural_headers = ['content-type'] +overzealous_headers = ['mime-version', 'content-transfer-encoding'] + +def encrypt(msg: EmailMessage, recipients: list[str]) -> tuple[EmailMessage, bool]: + payload = wrap_body(deepcopy(msg)) + + rcpt_keys = load_keys(recipients) + if len(rcpt_keys) < 1: + return msg, False + + enc_msg = pgpy.PGPMessage.new(payload.as_string()) + for key in rcpt_keys: + enc_msg = key.encrypt(enc_msg) + + container = MIMEMultipart( + 'encrypted', + boundary=gen_boundary(), + protocol='application/pgp-encrypted' + ) + container.preamble = 'This is an OpenPGP/MIME encrypted message (RFC 4880 and 3156)' + + part1 = MIMEApplication( + _data='Version: 1\n', + _subtype='pgp-encrypted', + _encoder=email.encoders.encode_7or8bit + ) + part1['Content-Description'] = 'PGP/MIME version identification' + + part2 = MIMEApplication( + _data=str(enc_msg), + _subtype='octet-stream; name="encrypted.asc"', + _encoder=email.encoders.encode_7or8bit + ) + part2['Content-Description'] = 'OpenPGP encrypted message' + part2['Content-Disposition'] = 'inline; filename="encrypted.asc"' + + strip_extraneous_headers(part1) + strip_extraneous_headers(part2) + container.attach(part1) + container.attach(part2) + strip_extraneous_headers(container, ['mime-version']) + return container, True + +def already_encrypted(msg: EmailMessage) -> bool: + if msg.get_content_type() in ['multipart/encrypted', 'application/pgp-encrypted']: + return True + for part in msg.iter_parts(): + if already_encrypted(part): + return True + return False + +def wrap_body(msg: EmailMessage) -> EmailMessage: + wrapped_msg = MIMEMultipart('mixed', boundary=gen_boundary(), protected_headers='v1') + strip_extraneous_headers(wrapped_msg, overzealous_headers + protected_headers) + copy_headers(msg, wrapped_msg, protected_headers) + + if msg.is_multipart(): + strip_extraneous_headers(wrapped_msg, structural_headers) + copy_headers(msg, wrapped_msg, structural_headers) + wrapped_msg.set_payload(msg.get_payload(decode=False)) + else: + text_holder = MIMEText(msg.get_payload(decode=True), _charset='utf-8') + strip_extraneous_headers(text_holder, structural_headers) + copy_headers(msg, text_holder, structural_headers) + wrapped_msg.attach(text_holder) + + return wrapped_msg + +def copy_headers(orig_msg: EmailMessage, container: EmailMessage, headers: list) -> None: + for (header, value) in orig_msg.items(): + if header.lower() in headers: + container.add_header(header, value) + +def strip_extraneous_headers(msg: EmailMessage, strip_headers=overzealous_headers) -> None: + for header in msg.keys(): + if header.lower() in strip_headers: + del msg[header] + +def gen_boundary() -> str: + return '-' * 12 + ''.join(alphabet_random(ascii_letters + digits, k=24)) + +def load_keys(recipients: list[str]) -> list[pgpy.PGPKey]: + addrs = [] + for recipient in recipients: + _display_name, addr = email.utils.parseaddr(recipient) + addrs.append(addr) + return key_loader.load_keys(addrs) |