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client_v2.py
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688 lines (560 loc) Β· 25.5 KB
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# -*- coding: utf-8 -*-
"""
Encrypted Dual-Stack Chat Client v2.0
Terminal-based chat client with Forward Secrecy (X3DH + Double Ratchet).
"""
import socket
import ssl
import threading
import json
import sys
import os
import base64
# Configure stdout for UTF-8 on Windows
if sys.platform == 'win32':
import codecs
if hasattr(sys.stdout, 'buffer'):
sys.stdout = codecs.getwriter('utf-8')(sys.stdout.buffer, 'strict')
sys.stderr = codecs.getwriter('utf-8')(sys.stderr.buffer, 'strict')
from datetime import datetime
import config
# Forward Secrecy imports
if config.E2E_ENABLED:
from x3dh import X3DHKeyManager, X3DHPreKeyBundle, x3dh_initiate, x3dh_respond
from double_ratchet import RatchetState, DoubleRatchet
from x25519_utils import X25519KeyPair, generate_fingerprint, generate_safety_number
class ChatClient:
"""Encrypted chat client with Forward Secrecy and dual-stack support."""
PROTOCOL_VERSION = "2.0" # Forward Secrecy protocol
def __init__(self, server_host, server_port, username, verify_cert=False):
self.server_host = server_host
self.server_port = server_port
self.username = username
self.verify_cert = verify_cert
self.socket = None
self.running = False
self.address_family = None
# Forward Secrecy (X3DH + Double Ratchet)
self.e2e_enabled = config.E2E_ENABLED
if self.e2e_enabled:
# X3DH key manager
self.x3dh_manager = X3DHKeyManager()
# Ratchet states for each peer
self.ratchet_states = {} # {username: DoubleRatchet}
self.ratchet_lock = threading.Lock()
# Peer X3DH bundles
self.peer_bundles = {} # {username: X3DHPreKeyBundle}
self.bundles_lock = threading.Lock()
# Track initialization
self.keys_initialized = False
# TOFU: Trust-on-First-Use for MITM protection
self.trusted_keys = {} # {username: identity_key_hex}
self.trusted_keys_file = 'trusted_keys.json'
self.load_trusted_keys()
def create_ssl_context(self):
"""Create SSL context for TLS encryption."""
ssl_context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
ssl_context.minimum_version = ssl.TLSVersion.TLSv1_2
if self.verify_cert:
ssl_context.verify_mode = ssl.CERT_REQUIRED
ssl_context.check_hostname = True
ssl_context.load_verify_locations(config.SERVER_CERT)
else:
ssl_context.check_hostname = False
ssl_context.verify_mode = ssl.CERT_NONE
return ssl_context
def detect_address_family(self):
"""Detect whether to use IPv4 or IPv6."""
if self.server_host.lower() == 'localhost':
return socket.AF_INET6
try:
socket.inet_pton(socket.AF_INET6, self.server_host)
return socket.AF_INET6
except socket.error:
pass
try:
socket.inet_pton(socket.AF_INET, self.server_host)
return socket.AF_INET
except socket.error:
pass
return socket.AF_INET6
def connect(self):
"""Connect to server with TLS encryption."""
self.address_family = self.detect_address_family()
family = self.address_family
protocol_name = "IPv6" if family == socket.AF_INET6 else "IPv4"
try:
raw_socket = socket.socket(family, socket.SOCK_STREAM)
raw_socket.settimeout(config.CLIENT_TIMEOUT)
print(f"Connecting to {self.server_host}:{self.server_port} using {protocol_name}...")
raw_socket.connect((self.server_host, self.server_port))
ssl_context = self.create_ssl_context()
self.socket = ssl_context.wrap_socket(
raw_socket,
server_hostname=None
)
print(f"[OK] Connected via {protocol_name}")
print(f"[OK] TLS encryption enabled ({self.socket.version()})")
print("=" * 60)
# Disable Nagle's algorithm for real-time delivery
self.socket.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
self.socket.settimeout(None)
return True
except socket.timeout:
print(f"[ERROR] Connection timeout", file=sys.stderr)
if self.server_host.lower() == 'localhost' and family == socket.AF_INET6:
print("Trying IPv4 fallback...", file=sys.stderr)
return self.connect_with_fallback()
return False
except ConnectionRefusedError:
print(f"[ERROR] Connection refused - is server running?", file=sys.stderr)
if self.server_host.lower() == 'localhost' and family == socket.AF_INET6:
print("Trying IPv4 fallback...", file=sys.stderr)
return self.connect_with_fallback()
return False
except Exception as e:
print(f"[ERROR] Connection error: {e}", file=sys.stderr)
return False
def connect_with_fallback(self):
"""Fallback to IPv4 if IPv6 fails."""
try:
raw_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
raw_socket.settimeout(config.CLIENT_TIMEOUT)
print(f"Connecting to {config.CLIENT_LOCALHOST_IPV4}:{self.server_port} using IPv4...")
raw_socket.connect((config.CLIENT_LOCALHOST_IPV4, self.server_port))
ssl_context = self.create_ssl_context()
self.socket = ssl_context.wrap_socket(raw_socket, server_hostname=None)
print(f"[OK] Connected via IPv4")
print(f"[OK] TLS encryption enabled ({self.socket.version()})")
print("=" * 60)
self.socket.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
self.socket.settimeout(None)
return True
except Exception as e:
print(f"[ERROR] IPv4 fallback failed: {e}", file=sys.stderr)
return False
def generate_keys(self):
"""Generate X3DH key bundle for Forward Secrecy."""
if not self.e2e_enabled:
return
# Generate X3DH key bundle
print("[E2E] Generating X3DH key bundle...")
bundle = self.x3dh_manager.get_prekey_bundle()
# Display identity key fingerprint
fingerprint = generate_fingerprint(self.x3dh_manager.identity_keypair.get_public_bytes())
print(f"[E2E] Identity key fingerprint:")
print(f" {fingerprint}")
print(f"[E2E] Protocol: Signal (X3DH + Double Ratchet)")
print(f"[E2E] Sending X3DH bundle with JOIN")
# Send JOIN with X3DH bundle
join_msg = {
'type': 'join',
'username': self.username,
'x3dh_bundle': bundle.to_dict(),
'protocol_version': '2.0'
}
self.send_message(join_msg)
def send_message(self, message):
"""Send JSON message to server."""
try:
data = json.dumps(message).encode('utf-8')
self.socket.sendall(data + b'\n')
except Exception as e:
print(f"\n[ERROR] Send failed: {e}", file=sys.stderr)
self.running = False
def load_trusted_keys(self):
"""Load trusted identity keys from disk (TOFU)."""
try:
if os.path.exists(self.trusted_keys_file):
with open(self.trusted_keys_file, 'r') as f:
self.trusted_keys = json.load(f)
print(f"[TOFU] Loaded {len(self.trusted_keys)} trusted key(s)")
except Exception as e:
print(f"[WARN] Could not load trusted keys: {e}")
self.trusted_keys = {}
def save_trusted_keys(self):
"""Save trusted identity keys to disk."""
try:
with open(self.trusted_keys_file, 'w') as f:
json.dump(self.trusted_keys, f, indent=2)
except Exception as e:
print(f"[WARN] Could not save trusted keys: {e}")
def verify_identity_key(self, username: str, identity_key: bytes) -> bool:
"""
Verify identity key using TOFU (Trust-on-First-Use).
Args:
username: Peer username
identity_key: Peer's identity public key
Returns:
True if key is trusted, False if rejected
"""
identity_key_hex = identity_key.hex()
stored_key = self.trusted_keys.get(username)
if stored_key is None:
# First contact - trust and store
fingerprint = generate_fingerprint(identity_key)
print(f"\n{'='*60}")
print(f"[TOFU] First contact with {username}")
print(f"{'='*60}")
print(f"Identity fingerprint:")
print(f" {fingerprint}")
print(f"\nThis key will be trusted for future sessions.")
print(f"Verify this fingerprint with {username} out-of-band")
print(f"(phone call, in person, etc.) to prevent MITM attacks.")
print(f"{'='*60}\n")
self.trusted_keys[username] = identity_key_hex
self.save_trusted_keys()
return True
if stored_key != identity_key_hex:
# KEY CHANGED - Potential MITM attack!
old_fingerprint = generate_fingerprint(bytes.fromhex(stored_key))
new_fingerprint = generate_fingerprint(identity_key)
print(f"\n{'='*60}")
print(f"β οΈ SECURITY WARNING: {username}'s key changed!")
print(f"{'='*60}")
print(f"Old fingerprint: {old_fingerprint}")
print(f"New fingerprint: {new_fingerprint}")
print(f"\nPossible reasons:")
print(f" 1. {username} reinstalled the app (legitimate)")
print(f" 2. Man-in-the-middle attack (DANGER!)")
print(f"\nβ οΈ DO NOT ACCEPT unless you verified with {username}!")
print(f"{'='*60}\n")
try:
response = input(f"Accept new key for {username}? (yes/no): ").strip().lower()
if response == 'yes':
self.trusted_keys[username] = identity_key_hex
self.save_trusted_keys()
print(f"[TOFU] Accepted new key for {username}")
return True
else:
print(f"[TOFU] Rejected new key for {username}")
return False
except (EOFError, KeyboardInterrupt):
print(f"\n[TOFU] Rejected new key for {username}")
return False
# Key matches - trusted
return True
def send_encrypted_message(self, plaintext: str):
"""
Encrypt and send message using Double Ratchet.
Messages are sent individually to each peer.
"""
if not self.e2e_enabled:
# Fallback to plaintext
self.send_message({'type': 'message', 'content': plaintext})
return
# Get all peers
with self.bundles_lock:
if not self.peer_bundles:
print("\n[WARN] No other users in chat yet.")
return
peers = list(self.peer_bundles.keys())
# Send to each peer individually
for peer in peers:
try:
# Get or initialize ratchet
with self.ratchet_lock:
if peer not in self.ratchet_states:
# Only initialize if we don't have a ratchet yet
self._initialize_ratchet_with_peer(peer)
ratchet = self.ratchet_states[peer]
# Encrypt with ratchet
ciphertext, header = ratchet.ratchet_encrypt(plaintext.encode())
# Include X3DH ephemeral key in first message if this is the initiator
if hasattr(ratchet, 'x3dh_ephemeral_pub'):
header['x3dh_ephemeral'] = ratchet.x3dh_ephemeral_pub.hex()
# Remove it after first use
delattr(ratchet, 'x3dh_ephemeral_pub')
# Send ratchet message
msg = {
'type': 'ratchet_message',
'sender': self.username,
'recipient': peer,
'header': header,
'ciphertext': base64.b64encode(ciphertext).decode(),
'timestamp': datetime.now().isoformat()
}
self.send_message(msg)
except Exception as e:
print(f"\n[ERROR] Failed to encrypt for {peer}: {e}", file=sys.stderr)
def _initialize_ratchet_with_peer(self, peer_username: str):
"""
Initialize Double Ratchet with a peer using X3DH (Alice's role).
Called when sending first message to a peer.
"""
# Get bundle with lock
with self.bundles_lock:
bundle = self.peer_bundles[peer_username]
# Perform X3DH as initiator
shared_secret, ephemeral_pub = x3dh_initiate(
self.x3dh_manager.identity_keypair,
bundle
)
# Initialize ratchet (we're Alice)
state = RatchetState.initialize_alice(shared_secret, bundle.signed_prekey)
ratchet = DoubleRatchet(state)
# Store X3DH ephemeral key for first message
# This is needed so the responder can derive the same shared secret
ratchet.x3dh_ephemeral_pub = ephemeral_pub
self.ratchet_states[peer_username] = ratchet
print(f"[E2E] Initialized ratchet with {peer_username} (initiator)")
def _initialize_ratchet_as_responder(self, sender: str, alice_ephemeral_pub: bytes):
"""
Initialize Double Ratchet when receiving first message (Bob's role).
"""
# Get bundle with lock
with self.bundles_lock:
sender_bundle = self.peer_bundles.get(sender)
if not sender_bundle:
raise Exception(f"No bundle for {sender}")
# Perform X3DH as responder
shared_secret = x3dh_respond(
self.x3dh_manager.identity_keypair,
self.x3dh_manager.signed_prekey_pair,
None, # One-time key tracking not implemented yet
sender_bundle.identity_key,
alice_ephemeral_pub
)
# Initialize ratchet (we're Bob)
state = RatchetState.initialize_bob(
shared_secret,
self.x3dh_manager.signed_prekey_pair
)
self.ratchet_states[sender] = DoubleRatchet(state)
print(f"[E2E] Initialized ratchet with {sender} (responder)")
def receive_messages(self):
"""Receive and handle messages from server."""
buffer = ""
while self.running:
try:
data = self.socket.recv(config.BUFFER_SIZE)
if not data:
print("\n[ERROR] Connection closed by server")
self.running = False
break
buffer += data.decode('utf-8')
while '\n' in buffer:
line, buffer = buffer.split('\n', 1)
if line.strip():
try:
message = json.loads(line)
self._handle_message(message)
except json.JSONDecodeError:
pass
except ConnectionResetError:
print("\n[ERROR] Connection reset")
self.running = False
break
except Exception as e:
if self.running:
print(f"\n[ERROR] Receive error: {e}", file=sys.stderr)
self.running = False
break
def _handle_message(self, message: dict):
"""Handle incoming message based on type."""
msg_type = message.get('type')
if msg_type == 'bundle_sync':
# Receive all existing bundles
bundles_dict = message.get('bundles', {})
with self.bundles_lock:
for username, bundle_dict in bundles_dict.items():
bundle = X3DHPreKeyBundle.from_dict(bundle_dict)
# TOFU: Verify identity key
if not self.verify_identity_key(username, bundle.identity_key):
print(f"[SECURITY] Rejected bundle from {username} - key verification failed")
continue
self.peer_bundles[username] = bundle
self.keys_initialized = True
if bundles_dict:
print(f"\n[E2E] Received {len(bundles_dict)} bundle(s)")
else:
print(f"\n[E2E] No other users yet (you're first)")
elif msg_type == 'key_bundle':
# New user's bundle
username = message.get('username')
bundle_dict = message.get('bundle')
if username and bundle_dict:
bundle = X3DHPreKeyBundle.from_dict(bundle_dict)
# TOFU: Verify identity key
if not self.verify_identity_key(username, bundle.identity_key):
print(f"[SECURITY] Rejected bundle from {username} - key verification failed")
return
with self.bundles_lock:
self.peer_bundles[username] = bundle
self.keys_initialized = True
print(f"[E2E] Received bundle for {username}")
elif msg_type == 'bundle_removal':
# User disconnected
username = message.get('username')
if username:
with self.bundles_lock:
if username in self.peer_bundles:
del self.peer_bundles[username]
with self.ratchet_lock:
if username in self.ratchet_states:
del self.ratchet_states[username]
print(f"\n[E2E] Removed bundle for {username}")
elif msg_type == 'ratchet_message':
# Encrypted message
self._handle_ratchet_message(message)
elif msg_type == 'system':
# System message
content = message.get('content', '')
print(f"\n[SYSTEM] {content}")
sys.stdout.flush()
print(f"{self.username}> ", end='', flush=True)
elif msg_type == 'message':
# Plaintext message (fallback)
username = message.get('username', 'Unknown')
content = message.get('content', '')
timestamp = message.get('timestamp', '')
try:
dt = datetime.fromisoformat(timestamp)
time_str = dt.strftime('%H:%M:%S')
except:
time_str = ''
if time_str:
print(f"\n[{time_str}] {username}: {content}")
else:
print(f"\n{username}: {content}")
sys.stdout.flush()
print(f"{self.username}> ", end='', flush=True)
def _handle_ratchet_message(self, message: dict):
"""Decrypt and display ratchet message."""
sender = message.get('sender')
header = message.get('header')
ciphertext_b64 = message.get('ciphertext')
timestamp = message.get('timestamp', '')
try:
ciphertext = base64.b64decode(ciphertext_b64)
# Get or initialize ratchet
with self.ratchet_lock:
if sender not in self.ratchet_states:
# First message from this sender - check for X3DH ephemeral key
if 'x3dh_ephemeral' in header:
# This is the first message, use X3DH ephemeral key
alice_ephemeral = bytes.fromhex(header['x3dh_ephemeral'])
else:
# Fallback to ratchet DH key (shouldn't happen in normal flow)
alice_ephemeral = bytes.fromhex(header['dh_public'])
self._initialize_ratchet_as_responder(sender, alice_ephemeral)
ratchet = self.ratchet_states[sender]
# Decrypt
plaintext = ratchet.ratchet_decrypt(ciphertext, header)
# Display
try:
dt = datetime.fromisoformat(timestamp)
time_str = dt.strftime('%H:%M:%S')
except:
time_str = ''
if time_str:
print(f"\n[{time_str}] [FS] {sender}: {plaintext.decode()}")
else:
print(f"\n[FS] {sender}: {plaintext.decode()}")
sys.stdout.flush()
print(f"{self.username}> ", end='', flush=True)
except Exception as e:
print(f"\n[ERROR] Decryption failed from {sender}: {e}", file=sys.stderr)
import traceback
traceback.print_exc()
sys.stdout.flush()
print(f"{self.username}> ", end='', flush=True)
def send_messages(self):
"""Handle user input and send messages."""
print()
print("Type your messages below. Press Ctrl+C to quit.")
print("=" * 60)
while self.running:
try:
user_input = input(f"{self.username}> ")
if not user_input.strip():
continue
# Send encrypted message
if self.e2e_enabled:
self.send_encrypted_message(user_input.strip())
else:
msg = {
'type': 'message',
'content': user_input.strip()
}
self.send_message(msg)
except EOFError:
break
except KeyboardInterrupt:
print("\n\nDisconnecting...")
break
except Exception as e:
print(f"\n[ERROR] {e}", file=sys.stderr)
break
def start(self):
"""Start the chat client."""
if not self.connect():
return False
self.running = True
# Receive welcome message
try:
data = self.socket.recv(config.BUFFER_SIZE)
if data:
message = json.loads(data.decode('utf-8'))
print(f"\n{message.get('content', '')}\n")
except:
pass
# Generate X3DH keys
if self.e2e_enabled:
self.generate_keys()
# Start receiver thread
receiver_thread = threading.Thread(
target=self.receive_messages,
daemon=True
)
receiver_thread.start()
# Handle sending in main thread
self.send_messages()
# Cleanup
self.running = False
if self.socket:
try:
self.socket.close()
except:
pass
print("Disconnected.")
return True
def stop(self):
"""Stop the client."""
self.running = False
def main():
"""Main entry point."""
print("=" * 60)
print(" Encrypted Chat Client v2.0")
print(" Forward Secrecy (Signal Protocol)")
print("=" * 60)
print()
try:
server = input(f"Server address (default: localhost): ").strip()
if not server:
server = "localhost"
port_input = input(f"Server port (default: {config.SERVER_PORT}): ").strip()
if port_input:
port = int(port_input)
else:
port = config.SERVER_PORT
username = input("Enter your username: ").strip()
if not username:
username = "Anonymous"
username = username[:config.USERNAME_MAX_LENGTH]
print()
except KeyboardInterrupt:
print("\n\nCancelled.")
return
except ValueError:
print("[ERROR] Invalid port number", file=sys.stderr)
return
client = ChatClient(server, port, username, verify_cert=False)
try:
client.start()
except KeyboardInterrupt:
print("\n\nDisconnecting...")
finally:
client.stop()
if __name__ == '__main__':
main()