mattia/smtp_app_proxy
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Some PGP advancement

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This commit is contained in:
Mattia Mascarello 2025-03-16 11:45:49 +01:00
parent 4900374cbd
commit ef4556f69e
3 changed files with 226 additions and 28 deletions
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4
config.example.yml
View File

@ -17,3 +17,7 @@ apps:
password: "pw1"
app2@localhost:
password: "pw2"
gpg:
home: "/home/user/.gnupg"
passphrase: "phrase"

248
proxy.py
View File

@ -4,13 +4,22 @@ import base64
import socket
import yaml
import signal
from email import message_from_bytes
from email.parser import BytesParser
from email.policy import default
from email.message import EmailMessage
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText
from email.mime.base import MIMEBase
from email.encoders import encode_base64
from aiosmtpd.controller import Controller
from aiosmtpd.smtp import AuthResult
from aiosmtpd.smtp import AuthResult, Envelope, Session
import gnupg
import sys
from watchdog.observers import Observer
from watchdog.events import FileSystemEventHandler
import requests
# ---------------------------
# Load Configuration
@ -46,17 +55,17 @@ def is_port_available(host: str, port: int) -> bool:
def setup_logging():
"""Set up logging configuration with a single stream handler."""
logger = logging.getLogger() # Get the root logger
# Set the logging level to DEBUG
logger.setLevel(logging.DEBUG)
# Create a stream handler to output logs to stdout
stream_handler = logging.StreamHandler(sys.stdout)
# Set the log format
formatter = logging.Formatter("%(asctime)s [%(levelname)s] %(message)s")
stream_handler.setFormatter(formatter)
# Add the handler to the logger
logger.addHandler(stream_handler)
@ -66,6 +75,7 @@ def setup_logging():
# Setup global logger
logger = setup_logging()
# ---------------------------
# Watchdog for Configuration Reload
# ---------------------------
@ -100,7 +110,14 @@ SMTP_PASSWORD = config["smtp_server"]["password"]
SMTP_FROM_NAME = config["smtp_server"]["from_name"]
SMTP_FROM_EMAIL = config["smtp_server"]["from_email"]
app_credentials = config["apps"] # Allowed users' credentials
APP_CREDENTIALS = config["apps"] # Allowed users' credentials
PASSPHRASE = config["gpg"]["passphrase"]
gpg = gnupg.GPG(gnupghome=config["gpg"]["home"])
gpg.encoding = "utf-8"
KEYSERVER_URL = "https://keys.openpgp.org/vks/v1/by-email/"
# ---------------------------
@ -112,7 +129,7 @@ class EmailAuthenticator:
"""
def __init__(self):
self.app_credentials = app_credentials
self.APP_CREDENTIALS = APP_CREDENTIALS
async def __call__(self, server, session, envelope, mechanism, auth_data):
fail_nothandled = AuthResult(success=False, handled=False)
@ -137,11 +154,16 @@ class EmailAuthenticator:
return fail_nothandled
username, password = decoded.split("\x00")
if username in self.app_credentials and self.app_credentials[username]["password"] == password:
if (
username in self.APP_CREDENTIALS
and self.APP_CREDENTIALS[username]["password"] == password
):
logger.info(f"✅ Authentication successful for {username}")
return AuthResult(success=True)
else:
logger.error(f"❌ Authentication failed for {username}: Incorrect password")
logger.error(
f"❌ Authentication failed for {username}: Incorrect password"
)
return fail_nothandled
except Exception as e:
@ -150,15 +172,15 @@ class EmailAuthenticator:
# ---------------------------
# EmailLoggingProxy Class
# EmailProxy Class
# ---------------------------
class EmailLoggingProxy:
class EmailProxy:
"""
Handler for incoming emails that logs the data, performs authentication,
rewrites the 'From' header, and forwards the email via the specified SMTP server.
"""
async def handle_EHLO(self, server, session, envelope, hostname):
async def handle_EHLO(self, server, session: Session, envelope: Envelope, hostname):
"""Handle the EHLO command and advertise AUTH support."""
session.host_name = hostname
return (
@ -170,7 +192,7 @@ class EmailLoggingProxy:
"250 HELP"
)
async def handle_DATA(self, server, session, envelope):
async def handle_DATA(self, server, session: Session, envelope: Envelope):
"""
Handle the DATA command, log the email, modify the From header,
and forward the email via the specified SMTP server.
@ -184,29 +206,193 @@ class EmailLoggingProxy:
# Log the email content
logger.debug(f"Mail data:\n{data.decode('utf-8', errors='replace')}")
# Validate sender against allowed app credentials
if mailfrom not in app_credentials:
logger.error(f"🚫 Unauthorized sender: {mailfrom}")
return "550 Unauthorized sender"
# Parse the email
msg = BytesParser(policy=default).parsebytes(data)
# Modify the "From" header with the configuration details
msg.replace_header("From", f"{SMTP_FROM_NAME} <{SMTP_FROM_EMAIL}>")
# Forward the email via the specified SMTP server
encrypted_recipients = []
unencrypted_recipients = []
for recipient in rcpttos:
if self.fetch_pgp_key(recipient):
encrypted_recipients.append(recipient)
else:
unencrypted_recipients.append(recipient)
bcc_recipients = []
if "Bcc" in msg:
bcc_recipients = msg["Bcc"].split(",")
del msg["Bcc"]
if encrypted_recipients:
encrypted_msg = self.encrypt_mime_email(msg, encrypted_recipients)
if encrypted_msg:
self.send_email(encrypted_msg, encrypted_recipients)
if unencrypted_recipients:
plaintext_msg = self.add_unencrypted_warning(msg)
self.send_email(plaintext_msg, unencrypted_recipients)
# Send separate emails to each BCC recipient for privacy
for bcc in bcc_recipients:
if bcc in encrypted_recipients:
self.send_email(self.encrypt_mime_email(msg, [bcc]), [bcc])
else:
self.send_email(self.add_unencrypted_warning(msg), [bcc])
return "250 OK"
def fetch_pgp_key(self, email):
"""Checks if a PGP key exists locally or fetches it from the keyserver."""
# Check if the key exists locally
keys = gpg.list_keys(keys=email)
if keys:
logger.info(f"✅ PGP key for {email} found locally.")
return True # Key exists locally
# Key does not exist locally, so try fetching from the keyserver
logger.info(f"🔍 Looking up PGP key for {email} on keyserver...")
# Request the key from the keyserver API
keyserver_url = f"{KEYSERVER_URL}{email}"
try:
logger.info(f"📤 Forwarding email to {rcpttos} via SMTP server...")
response = requests.get(keyserver_url)
if response.status_code == 200:
key_data = response.text
logger.info(
f"✅ Successfully retrieved PGP key for {email} from keyserver."
)
# Import the key into GPG
import_result = gpg.import_keys(key_data)
if import_result.count > 0:
logger.info(
f"✅ PGP key for {email} successfully imported into GPG."
)
return True
else:
logger.warning(f"❌ Failed to import PGP key for {email}.")
return False
else:
logger.warning(
f"❌ No PGP key found for {email}. HTTP status code: {response.status_code}"
)
return False
except requests.exceptions.RequestException as e:
logger.error(f"❌ Error while contacting keyserver: {e}")
return False
def encrypt_mime_email(self, msg, recipients):
"""Encrypts a full email as PGP/MIME with multiple recipients and hides the subject."""
original_subject = msg["Subject"]
msg.replace_header("Subject", "...")
# Convert email to MIME
mime_msg = MIMEMultipart()
mime_msg["Subject"] = "..."
mime_msg["From"] = msg["From"]
mime_msg["To"] = ", ".join(recipients)
# Add original subject inside encrypted content
text_part = MIMEText(f"Subject: {original_subject}\n\n{msg.as_string()}")
mime_msg.attach(text_part)
# Encrypt with all recipient keys
encrypted_data = gpg.encrypt(
mime_msg.as_string(),
recipients=recipients,
sign=SMTP_FROM_EMAIL,
always_trust=True,
passphrase=PASSPHRASE,
)
if not encrypted_data.ok:
logger.error(f"❌ Encryption failed: {encrypted_data.stderr}")
return None
# Create PGP/MIME encrypted email
encrypted_email = MIMEMultipart(
"encrypted", protocol="application/pgp-encrypted"
)
encrypted_email["Subject"] = "Encrypted Message"
encrypted_email["From"] = msg["From"]
encrypted_email["To"] = ", ".join(recipients)
# PGP version header
pgp_header = MIMEBase("application", "pgp-encrypted")
pgp_header.add_header("Content-Description", "PGP/MIME Versions Header")
pgp_header.set_payload("Version: 1\r\n")
encrypted_email.attach(pgp_header)
# Encrypted email payload
encrypted_part = MIMEBase("application", "octet-stream")
encrypted_part.set_payload(str(encrypted_data))
encrypted_part.add_header(
"Content-Disposition", "inline", filename="encrypted.asc"
)
encrypted_email.attach(encrypted_part)
return encrypted_email
def add_unencrypted_warning(self, msg):
"""Adds a warning footer to unencrypted emails for both plain-text and HTML bodies."""
warning_text = (
"\n\n⚠️ This email was sent without end-to-end encryption.\n"
"This mail server supports automatic PGP encryption.\n"
"Consider setting up a PGP key and publishing it to a keyserver (e.g., keys.openpgp.org)."
)
# For multipart emails (text/plain + text/html)
if msg.is_multipart():
for part in msg.walk():
# Check if the part is plain text
if part.get_content_type() == "text/plain":
part.set_payload(part.get_payload() + warning_text)
# Check if the part is HTML text
elif part.get_content_type() == "text/html":
html_warning = (
f"<p><strong>⚠️ This email was sent without end-to-end encryption.</strong><br>"
f"This mail server supports automatic PGP encryption.<br>"
f"Consider setting up a PGP key and publishing it to a keyserver "
f"(e.g., keys.openpgp.org).</p>"
)
part.set_payload(part.get_payload() + html_warning)
part.replace_header(
"Content-Transfer-Encoding", "quoted-printable"
) # Ensure HTML part is encoded correctly
else:
# If it's a non-multipart message (either plain-text or HTML only)
if msg.get_content_type() == "text/plain":
msg.set_payload(msg.get_payload() + warning_text)
elif msg.get_content_type() == "text/html":
html_warning = (
f"<p><strong>⚠️ This email was sent without end-to-end encryption.</strong><br>"
f"This mail server supports automatic PGP encryption.<br>"
f"Consider setting up a PGP key and publishing it to a keyserver "
f"(e.g., keys.openpgp.org).</p>"
)
msg.set_payload(msg.get_payload() + html_warning)
msg.replace_header("Content-Transfer-Encoding", "quoted-printable")
return msg
def send_email(self, msg, recipients):
"""Sends an email via SMTP, ensuring BCC recipients remain private."""
try:
logger.info(f"📤 Sending email to {recipients} via SMTP...")
with smtplib.SMTP(SMTP_SERVER_HOST, SMTP_SERVER_PORT) as smtp_server:
smtp_server.starttls() # Upgrade connection to TLS
smtp_server.starttls()
smtp_server.login(SMTP_USER, SMTP_PASSWORD)
smtp_server.sendmail(SMTP_FROM_EMAIL, rcpttos, msg.as_bytes())
logger.info(f"✅ Email successfully forwarded to {rcpttos}")
return "250 OK"
smtp_server.sendmail(SMTP_FROM_EMAIL, recipients, msg.as_bytes())
logger.info(f"✅ Email successfully sent to {recipients}")
except Exception as e:
logger.error(f"❌ Failed to send email: {e}")
return "550 Internal server error"
# ---------------------------
@ -223,9 +409,15 @@ def run_proxy():
authenticator = EmailAuthenticator()
# Create the SMTP instance and pass it as handler to the Controller
smtp_handler = EmailLoggingProxy()
controller = Controller(smtp_handler, hostname=PROXY_HOST, port=PROXY_PORT, authenticator=authenticator, auth_require_tls=False)
smtp_handler = EmailProxy()
controller = Controller(
smtp_handler,
hostname=PROXY_HOST,
port=PROXY_PORT,
authenticator=authenticator,
auth_require_tls=False,
)
# Start the config file watcher in a separate thread
config_watcher = Observer()
config_watcher.schedule(ConfigReloadHandler(), ".", recursive=False)

2
requirements.txt
View File

@ -1,3 +1,5 @@
aiosmtpd==1.4.6
PyYAML==6.0.2
watchdog==6.0.0
python-gnupg==0.5.4
requests==2.32.3