Merge branch 'Protocol_00' of git.gmoker.com:icing/monorepo into Protocol_00

protocol_prototype/IcingProtocol.drawio

@@ -260,11 +260,11 @@
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protocol_prototype/auto_mode.py

@@ -0,0 +1,430 @@
+import time
+import threading
+import queue
+from typing import Optional, Dict, Any, List, Callable, Tuple
+
+# ANSI colors for logging
+RED = "\033[91m"
+GREEN = "\033[92m"
+YELLOW = "\033[93m"
+BLUE = "\033[94m"
+RESET = "\033[0m"
+
+class AutoModeConfig:
+    """Configuration parameters for the automatic mode behavior."""
+    def __init__(self):
+        # Ping behavior
+        self.ping_response_accept = True  # Whether to accept incoming pings
+        self.ping_auto_initiate = False   # Whether to initiate pings when connected
+        self.ping_retry_count = 3         # Number of ping retries
+        self.ping_retry_delay = 5.0       # Seconds between ping retries
+        self.ping_timeout = 10.0          # Seconds to wait for ping response
+        self.preferred_cipher = 0         # 0=AES-GCM, 1=ChaCha20-Poly1305
+        
+        # Handshake behavior
+        self.handshake_retry_count = 3    # Number of handshake retries
+        self.handshake_retry_delay = 5.0  # Seconds between handshake retries
+        self.handshake_timeout = 10.0     # Seconds to wait for handshake
+        
+        # Messaging behavior
+        self.auto_message_enabled = False # Whether to auto-send messages
+        self.message_interval = 10.0      # Seconds between auto messages
+        self.message_content = "Hello, secure world!"  # Default message
+        
+        # General behavior
+        self.active_mode = False          # If true, initiates protocol instead of waiting
+
+
+class AutoMode:
+    """
+    Manages automated behavior for the Icing protocol.
+    Handles automatic progression through the protocol stages:
+    1. Connection setup
+    2. Ping/discovery
+    3. Key exchange
+    4. Encrypted communication
+    """
+    
+    def __init__(self, protocol_interface):
+        """
+        Initialize the AutoMode manager.
+        
+        Args:
+            protocol_interface: An object implementing the required protocol methods
+        """
+        self.protocol = protocol_interface
+        self.config = AutoModeConfig()
+        self.active = False
+        self.state = "idle"
+        
+        # Message queue for automated sending
+        self.message_queue = queue.Queue()
+        
+        # Tracking variables
+        self.ping_attempts = 0
+        self.handshake_attempts = 0
+        self.last_action_time = 0
+        self.timer_tasks = []  # List of active timer tasks (for cleanup)
+        
+    def start(self):
+        """Start the automatic mode."""
+        if self.active:
+            return
+
+        self.active = True
+        self.state = "idle"
+        self.ping_attempts = 0
+        self.handshake_attempts = 0
+        self.last_action_time = time.time()
+        
+        self._log_info("Automatic mode started")
+        
+        # Start in active mode if configured
+        if self.config.active_mode and self.protocol.connections:
+            self._start_ping_sequence()
+            
+    def stop(self):
+        """Stop the automatic mode and clean up any pending tasks."""
+        if not self.active:
+            return
+            
+        # Cancel any pending timers
+        for timer in self.timer_tasks:
+            if timer.is_alive():
+                timer.cancel()
+        self.timer_tasks = []
+        
+        self.active = False
+        self.state = "idle"
+        self._log_info("Automatic mode stopped")
+    
+    def handle_connection_established(self):
+        """Called when a new connection is established."""
+        if not self.active:
+            return
+            
+        self._log_info("Connection established")
+        
+        # If in active mode, start pinging
+        if self.config.active_mode:
+            self._start_ping_sequence()
+    
+    def handle_ping_received(self, index: int):
+        """
+        Handle a received ping request.
+        
+        Args:
+            index: Index of the ping request in the protocol's inbound message queue
+        """
+        if not self.active or not self._is_valid_message_index(index):
+            return
+            
+        self._log_info(f"Ping request received (index={index})")
+        
+        # Automatically respond to ping if configured to accept
+        if self.config.ping_response_accept:
+            self._log_info(f"Auto-responding to ping with accept={self.config.ping_response_accept}")
+            try:
+                # Schedule the response with a small delay to simulate real behavior
+                timer = threading.Timer(0.5, self._respond_to_ping, args=[index])
+                timer.daemon = True
+                timer.start()
+                self.timer_tasks.append(timer)
+            except Exception as e:
+                self._log_error(f"Failed to auto-respond to ping: {e}")
+    
+    def handle_ping_response_received(self, accepted: bool):
+        """
+        Handle a received ping response.
+        
+        Args:
+            accepted: Whether the ping was accepted
+        """
+        if not self.active:
+            return
+            
+        self.ping_attempts = 0  # Reset ping attempts counter
+        
+        if accepted:
+            self._log_info("Ping accepted! Proceeding with handshake")
+            # Send handshake if not already done
+            if self.state != "handshake_sent":
+                self._ensure_ephemeral_keys()
+                self._start_handshake_sequence()
+        else:
+            self._log_info("Ping rejected by peer. Stopping auto-protocol sequence.")
+            self.state = "idle"
+    
+    def handle_handshake_received(self, index: int):
+        """
+        Handle a received handshake.
+        
+        Args:
+            index: Index of the handshake in the protocol's inbound message queue
+        """
+        if not self.active or not self._is_valid_message_index(index):
+            return
+            
+        self._log_info(f"Handshake received (index={index})")
+        
+        try:
+            # Ensure we have ephemeral keys
+            self._ensure_ephemeral_keys()
+            
+            # Process the handshake (compute ECDH)
+            self.protocol.generate_ecdhe(index)
+            
+            # Derive HKDF key
+            self.protocol.derive_hkdf()
+            
+            # If we haven't sent our handshake yet, send it
+            if self.state != "handshake_sent":
+                timer = threading.Timer(0.5, self.protocol.send_handshake)
+                timer.daemon = True
+                timer.start()
+                self.timer_tasks.append(timer)
+                self.state = "handshake_sent"
+            else:
+                self.state = "key_exchange_complete"
+                
+            # Start sending queued messages if auto messaging is enabled
+            if self.config.auto_message_enabled:
+                self._start_message_sequence()
+                
+        except Exception as e:
+            self._log_error(f"Failed to process handshake: {e}")
+    
+    def handle_encrypted_received(self, index: int):
+        """
+        Handle a received encrypted message.
+        
+        Args:
+            index: Index of the encrypted message in the protocol's inbound message queue
+        """
+        if not self.active or not self._is_valid_message_index(index):
+            return
+            
+        # Try to decrypt automatically
+        try:
+            plaintext = self.protocol.decrypt_received_message(index)
+            self._log_info(f"Auto-decrypted message: {plaintext}")
+        except Exception as e:
+            self._log_error(f"Failed to auto-decrypt message: {e}")
+    
+    def queue_message(self, message: str):
+        """
+        Add a message to the auto-send queue.
+        
+        Args:
+            message: Message text to send
+        """
+        self.message_queue.put(message)
+        self._log_info(f"Message queued for sending: {message}")
+        
+        # If we're in the right state, start sending messages
+        if self.active and self.state == "key_exchange_complete" and self.config.auto_message_enabled:
+            self._process_message_queue()
+    
+    def _start_ping_sequence(self):
+        """Start the ping sequence to discover the peer."""
+        if self.ping_attempts >= self.config.ping_retry_count:
+            self._log_warning(f"Maximum ping attempts ({self.config.ping_retry_count}) reached")
+            self.state = "idle"
+            return
+            
+        self.state = "pinging"
+        self.ping_attempts += 1
+        
+        self._log_info(f"Sending ping request (attempt {self.ping_attempts}/{self.config.ping_retry_count})")
+        try:
+            self.protocol.send_ping_request(self.config.preferred_cipher)
+            self.last_action_time = time.time()
+            
+            # Schedule next ping attempt if needed
+            timer = threading.Timer(
+                self.config.ping_retry_delay, 
+                self._check_ping_response
+            )
+            timer.daemon = True
+            timer.start()
+            self.timer_tasks.append(timer)
+            
+        except Exception as e:
+            self._log_error(f"Failed to send ping: {e}")
+    
+    def _check_ping_response(self):
+        """Check if we got a ping response, retry if not."""
+        if not self.active or self.state != "pinging":
+            return
+            
+        # If we've waited long enough for a response, retry
+        if time.time() - self.last_action_time >= self.config.ping_timeout:
+            self._log_warning("No ping response received, retrying")
+            self._start_ping_sequence()
+    
+    def _respond_to_ping(self, index: int):
+        """
+        Respond to a ping request.
+        
+        Args:
+            index: Index of the ping request in the inbound messages
+        """
+        if not self.active or not self._is_valid_message_index(index):
+            return
+            
+        try:
+            answer = 1 if self.config.ping_response_accept else 0
+            self.protocol.respond_to_ping(index, answer)
+            
+            if answer == 1:
+                # If we accepted, we should expect a handshake
+                self.state = "accepted_ping"
+                self._ensure_ephemeral_keys()
+                
+                # Set a timer to send our handshake if we don't receive one
+                timer = threading.Timer(
+                    self.config.handshake_timeout,
+                    self._check_handshake_received
+                )
+                timer.daemon = True
+                timer.start()
+                self.timer_tasks.append(timer)
+                self.last_action_time = time.time()
+                
+        except Exception as e:
+            self._log_error(f"Failed to respond to ping: {e}")
+    
+    def _check_handshake_received(self):
+        """Check if we've received a handshake after accepting a ping."""
+        if not self.active or self.state != "accepted_ping":
+            return
+            
+        # If we've waited long enough and haven't received a handshake, initiate one
+        if time.time() - self.last_action_time >= self.config.handshake_timeout:
+            self._log_warning("No handshake received after accepting ping, initiating handshake")
+            self._start_handshake_sequence()
+    
+    def _start_handshake_sequence(self):
+        """Start the handshake sequence."""
+        if self.handshake_attempts >= self.config.handshake_retry_count:
+            self._log_warning(f"Maximum handshake attempts ({self.config.handshake_retry_count}) reached")
+            self.state = "idle"
+            return
+            
+        self.state = "handshake_sent"
+        self.handshake_attempts += 1
+        
+        self._log_info(f"Sending handshake (attempt {self.handshake_attempts}/{self.config.handshake_retry_count})")
+        try:
+            self.protocol.send_handshake()
+            self.last_action_time = time.time()
+            
+            # Schedule handshake retry check
+            timer = threading.Timer(
+                self.config.handshake_retry_delay,
+                self._check_handshake_response
+            )
+            timer.daemon = True
+            timer.start()
+            self.timer_tasks.append(timer)
+            
+        except Exception as e:
+            self._log_error(f"Failed to send handshake: {e}")
+    
+    def _check_handshake_response(self):
+        """Check if we've completed the key exchange, retry handshake if not."""
+        if not self.active or self.state != "handshake_sent":
+            return
+            
+        # If we've waited long enough for a response, retry
+        if time.time() - self.last_action_time >= self.config.handshake_timeout:
+            self._log_warning("No handshake response received, retrying")
+            self._start_handshake_sequence()
+    
+    def _start_message_sequence(self):
+        """Start the automated message sending sequence."""
+        if not self.config.auto_message_enabled:
+            return
+            
+        self._log_info("Starting automated message sequence")
+        
+        # Add the default message if queue is empty
+        if self.message_queue.empty():
+            self.message_queue.put(self.config.message_content)
+            
+        # Start processing the queue
+        self._process_message_queue()
+    
+    def _process_message_queue(self):
+        """Process messages in the queue and send them."""
+        if not self.active or self.state != "key_exchange_complete" or not self.config.auto_message_enabled:
+            return
+            
+        if not self.message_queue.empty():
+            message = self.message_queue.get()
+            self._log_info(f"Sending queued message: {message}")
+            
+            try:
+                self.protocol.send_encrypted_message(message)
+                
+                # Schedule next message send
+                timer = threading.Timer(
+                    self.config.message_interval,
+                    self._process_message_queue
+                )
+                timer.daemon = True
+                timer.start()
+                self.timer_tasks.append(timer)
+                
+            except Exception as e:
+                self._log_error(f"Failed to send queued message: {e}")
+                # Put the message back in the queue
+                self.message_queue.put(message)
+    
+    def _ensure_ephemeral_keys(self):
+        """Ensure ephemeral keys are generated if needed."""
+        if not hasattr(self.protocol, 'ephemeral_pubkey') or self.protocol.ephemeral_pubkey is None:
+            self._log_info("Generating ephemeral keys")
+            self.protocol.generate_ephemeral_keys()
+            
+    def _is_valid_message_index(self, index: int) -> bool:
+        """
+        Check if a message index is valid in the protocol's inbound_messages queue.
+        
+        Args:
+            index: The index to check
+            
+        Returns:
+            bool: True if the index is valid, False otherwise
+        """
+        if not hasattr(self.protocol, 'inbound_messages'):
+            self._log_error("Protocol has no inbound_messages attribute")
+            return False
+            
+        if index < 0 or index >= len(self.protocol.inbound_messages):
+            self._log_error(f"Invalid message index: {index}")
+            return False
+            
+        return True
+    
+    # Helper methods for logging
+    def _log_info(self, message: str):
+        print(f"{BLUE}[AUTO]{RESET} {message}")
+        if hasattr(self, 'verbose_logging') and self.verbose_logging:
+            state_info = f"(state={self.state})"
+            if 'pinging' in self.state and hasattr(self, 'ping_attempts'):
+                state_info += f", attempts={self.ping_attempts}/{self.config.ping_retry_count}"
+            elif 'handshake' in self.state and hasattr(self, 'handshake_attempts'):
+                state_info += f", attempts={self.handshake_attempts}/{self.config.handshake_retry_count}"
+            print(f"{BLUE}[AUTO-DETAIL]{RESET} {state_info}")
+        
+    def _log_warning(self, message: str):
+        print(f"{YELLOW}[AUTO-WARN]{RESET} {message}")
+        if hasattr(self, 'verbose_logging') and self.verbose_logging:
+            timer_info = f"Active timers: {len(self.timer_tasks)}"
+            print(f"{YELLOW}[AUTO-WARN-DETAIL]{RESET} {timer_info}")
+        
+    def _log_error(self, message: str):
+        print(f"{RED}[AUTO-ERROR]{RESET} {message}")
+        if hasattr(self, 'verbose_logging') and self.verbose_logging:
+            print(f"{RED}[AUTO-ERROR-DETAIL]{RESET} Current state: {self.state}, Active: {self.active}") 

protocol_prototype/cli.py

@@ -1,113 +1,328 @@
 import sys
+import argparse
+import shlex
 from protocol import IcingProtocol
 
 RED = "\033[91m"
 GREEN = "\033[92m"
 YELLOW = "\033[93m"
 BLUE = "\033[94m"
+MAGENTA = "\033[95m"
+CYAN = "\033[96m"
 RESET = "\033[0m"
 
+def print_help():
+    """Display all available commands."""
+    print(f"\n{YELLOW}=== Available Commands ==={RESET}")
+    print(f"\n{CYAN}Basic Protocol Commands:{RESET}")
+    print("  help                       - Show this help message")
+    print("  peer_id <hex_pubkey>       - Set peer identity public key")
+    print("  connect <port>             - Connect to a peer at the specified port")
+    print("  show_state                 - Display current protocol state")
+    print("  exit                       - Exit the program")
+    
+    print(f"\n{CYAN}Manual Protocol Operation:{RESET}")
+    print("  generate_ephemeral_keys    - Generate ephemeral ECDH keys")
+    print("  send_ping [cipher]         - Send PING request (cipher: 0=AES-GCM, 1=ChaCha20-Poly1305, default: 0)")
+    print("  respond_ping <index> <0|1> - Respond to a PING (0=reject, 1=accept)")
+    print("  send_handshake             - Send handshake with ephemeral keys")
+    print("  generate_ecdhe <index>     - Process handshake at specified index")
+    print("  derive_hkdf                - Derive encryption key using HKDF")
+    print("  send_encrypted <plaintext> - Encrypt and send a message")
+    print("  decrypt <index>            - Decrypt received message at index")
+    
+    print(f"\n{CYAN}Automatic Mode Commands:{RESET}")
+    print("  auto start                 - Start automatic mode")
+    print("  auto stop                  - Stop automatic mode")
+    print("  auto status                - Show current auto mode status and configuration")
+    print("  auto config <param> <value> - Configure auto mode parameters")
+    print("  auto config list           - Show all configurable parameters")
+    print("  auto message <text>        - Queue message for automatic sending")
+    print("  auto passive               - Configure as passive peer (responds to pings but doesn't initiate)")
+    print("  auto active                - Configure as active peer (initiates protocol)")
+    print("  auto log                   - Toggle detailed logging for auto mode")
+    
+    print(f"\n{CYAN}Debugging Commands:{RESET}")
+    print("  debug_message <index>      - Display detailed information about a message in the queue")
+    
+    print(f"\n{CYAN}Legacy Commands:{RESET}")
+    print("  auto_responder <on|off>    - Enable/disable legacy auto responder (deprecated)")
+
 
 def main():
     protocol = IcingProtocol()
 
     print(f"{YELLOW}\n======================================")
-    print("   Icing Protocol - Manual CLI Demo   ")
+    print("   Icing Protocol - Secure Communication   ")
     print("======================================\n" + RESET)
-
     print(f"Listening on port: {protocol.local_port}")
     print(f"Your identity public key (hex): {protocol.identity_pubkey.hex()}")
-    print("\nAvailable commands:")
+    print_help()
-    print("  set_peer_identity <hex_pubkey>")
-    print("  connect <port>")
-    print("  generate_ephemeral_keys")
-    print("  send_ping")
-    print("  send_handshake")
-    print("  respond_ping <index> <0|1>")
-    print("  generate_ecdhe <index>")
-    print("  auto_responder <on|off>")
-    print("  show_state")
-    print("  exit\n")
 
     while True:
         try:
-            line = input("Cmd> ").strip()
+            line = input(f"{MAGENTA}Cmd>{RESET} ").strip()
         except EOFError:
             break
         if not line:
             continue
             
-        parts = line.split()
+        parts = shlex.split(line)  # Handle quoted arguments properly
         cmd = parts[0].lower()
         
-        if cmd == "exit":
+        try:
-            protocol.stop()
+            # Basic commands
-            sys.exit(0)
+            if cmd == "exit":
+                protocol.stop()
+                break
                 
-        elif cmd == "show_state":
+            elif cmd == "help":
-            protocol.show_state()
+                print_help()
                 
-        elif cmd == "set_peer_identity":
+            elif cmd == "show_state":
-            if len(parts) != 2:
+                protocol.show_state()
-                print(f"{RED}Usage: set_peer_identity <hex_pubkey>{RESET}")
-                continue
-            protocol.set_peer_identity(parts[1])
                 
-        elif cmd == "connect":
+            elif cmd == "peer_id":
-            if len(parts) != 2:
+                if len(parts) != 2:
-                print(f"{RED}Usage: connect <port>{RESET}")
+                    print(f"{RED}[ERROR]{RESET} Usage: peer_id <hex_pubkey>")
-                continue
+                    continue
-            try:
+                try:
-                port = int(parts[1])
+                    protocol.set_peer_identity(parts[1])
-                protocol.connect_to_peer(port)
+                except ValueError as e:
-            except ValueError:
+                    print(f"{RED}[ERROR]{RESET} Invalid public key: {e}")
-                print(f"{RED}Invalid port.{RESET}")
                     
-        elif cmd == "generate_ephemeral_keys":
+            elif cmd == "connect":
-            protocol.generate_ephemeral_keys()
+                if len(parts) != 2:
+                    print(f"{RED}[ERROR]{RESET} Usage: connect <port>")
+                    continue
+                try:
+                    port = int(parts[1])
+                    protocol.connect_to_peer(port)
+                except ValueError:
+                    print(f"{RED}[ERROR]{RESET} Invalid port number.")
+                except Exception as e:
+                    print(f"{RED}[ERROR]{RESET} Connection failed: {e}")
             
-        elif cmd == "send_ping":
+            # Manual protocol operation
-            protocol.send_ping_request()
+            elif cmd == "generate_ephemeral_keys":
+                protocol.generate_ephemeral_keys()
                 
-        elif cmd == "send_handshake":
+            elif cmd == "send_ping":
-            protocol.send_handshake()
+                # Optional cipher parameter (0 = AES-GCM, 1 = ChaCha20-Poly1305)
+                cipher = 0  # Default to AES-GCM
+                if len(parts) >= 2:
+                    try:
+                        cipher = int(parts[1])
+                        if cipher not in (0, 1):
+                            print(f"{YELLOW}[WARNING]{RESET} Unsupported cipher code {cipher}. Using AES-GCM (0).")
+                            cipher = 0
+                    except ValueError:
+                        print(f"{YELLOW}[WARNING]{RESET} Invalid cipher code. Using AES-GCM (0).")
+                protocol.send_ping_request(cipher)
                 
-        elif cmd == "respond_ping":
+            elif cmd == "send_handshake":
-            if len(parts) != 3:
+                protocol.send_handshake()
-                print(f"{RED}Usage: respond_ping <index> <answer_code>{RESET}")
-                continue
-            try:
-                idx = int(parts[1])
-                ac = int(parts[2])
-                protocol.respond_to_ping(idx, ac)
-            except ValueError:
-                print(f"{RED}Index and answer_code must be integers.{RESET}")
                 
-        elif cmd == "generate_ecdhe":
+            elif cmd == "respond_ping":
-            if len(parts) != 2:
+                if len(parts) != 3:
-                print(f"{RED}Usage: generate_ecdhe <index>{RESET}")
+                    print(f"{RED}[ERROR]{RESET} Usage: respond_ping <index> <0|1>")
-                continue
+                    continue
-            try:
+                try:
-                idx = int(parts[1])
+                    idx = int(parts[1])
-                protocol.generate_ecdhe(idx)
+                    answer = int(parts[2])
-            except ValueError:
+                    if answer not in (0, 1):
-                print(f"{RED}Index must be an integer.{RESET}")
+                        print(f"{RED}[ERROR]{RESET} Answer must be 0 (reject) or 1 (accept).")
+                        continue
+                    protocol.respond_to_ping(idx, answer)
+                except ValueError:
+                    print(f"{RED}[ERROR]{RESET} Index and answer must be integers.")
+                except Exception as e:
+                    print(f"{RED}[ERROR]{RESET} Failed to respond to ping: {e}")
+                    
+            elif cmd == "generate_ecdhe":
+                if len(parts) != 2:
+                    print(f"{RED}[ERROR]{RESET} Usage: generate_ecdhe <index>")
+                    continue
+                try:
+                    idx = int(parts[1])
+                    protocol.generate_ecdhe(idx)
+                except ValueError:
+                    print(f"{RED}[ERROR]{RESET} Index must be an integer.")
+                except Exception as e:
+                    print(f"{RED}[ERROR]{RESET} Failed to process handshake: {e}")
+                    
+            elif cmd == "derive_hkdf":
+                try:
+                    protocol.derive_hkdf()
+                except Exception as e:
+                    print(f"{RED}[ERROR]{RESET} Failed to derive HKDF key: {e}")
+                    
+            elif cmd == "send_encrypted":
+                if len(parts) < 2:
+                    print(f"{RED}[ERROR]{RESET} Usage: send_encrypted <plaintext>")
+                    continue
+                plaintext = " ".join(parts[1:])
+                try:
+                    protocol.send_encrypted_message(plaintext)
+                except Exception as e:
+                    print(f"{RED}[ERROR]{RESET} Failed to send encrypted message: {e}")
+                    
+            elif cmd == "decrypt":
+                if len(parts) != 2:
+                    print(f"{RED}[ERROR]{RESET} Usage: decrypt <index>")
+                    continue
+                try:
+                    idx = int(parts[1])
+                    protocol.decrypt_received_message(idx)
+                except ValueError:
+                    print(f"{RED}[ERROR]{RESET} Index must be an integer.")
+                except Exception as e:
+                    print(f"{RED}[ERROR]{RESET} Failed to decrypt message: {e}")
+                    
+            # Debugging commands
+            elif cmd == "debug_message":
+                if len(parts) != 2:
+                    print(f"{RED}[ERROR]{RESET} Usage: debug_message <index>")
+                    continue
+                try:
+                    idx = int(parts[1])
+                    protocol.debug_message(idx)
+                except ValueError:
+                    print(f"{RED}[ERROR]{RESET} Index must be an integer.")
+                except Exception as e:
+                    print(f"{RED}[ERROR]{RESET} Failed to debug message: {e}")
+            
+            # Automatic mode commands
+            elif cmd == "auto":
+                if len(parts) < 2:
+                    print(f"{RED}[ERROR]{RESET} Usage: auto <command> [options]")
+                    print("Available commands: start, stop, status, config, message, passive, active")
+                    continue
+                
+                subcmd = parts[1].lower()
+                
+                if subcmd == "start":
+                    protocol.start_auto_mode()
+                    print(f"{GREEN}[AUTO]{RESET} Automatic mode started")
+                
+                elif subcmd == "stop":
+                    protocol.stop_auto_mode()
+                    print(f"{GREEN}[AUTO]{RESET} Automatic mode stopped")
+                
+                elif subcmd == "status":
+                    config = protocol.get_auto_mode_config()
+                    print(f"{YELLOW}=== Auto Mode Status ==={RESET}")
+                    print(f"Active: {protocol.auto_mode.active}")
+                    print(f"State: {protocol.auto_mode.state}")
+                    print(f"\n{YELLOW}--- Configuration ---{RESET}")
+                    for key, value in vars(config).items():
+                        print(f"  {key}: {value}")
+                
+                elif subcmd == "config":
+                    if len(parts) < 3:
+                        print(f"{RED}[ERROR]{RESET} Usage: auto config <param> <value> or auto config list")
+                        continue
+                        
+                    if parts[2].lower() == "list":
+                        config = protocol.get_auto_mode_config()
+                        print(f"{YELLOW}=== Auto Mode Configuration Parameters ==={RESET}")
+                        for key, value in vars(config).items():
+                            print(f"  {key} ({type(value).__name__}): {value}")
+                        continue
+                    
+                    if len(parts) != 4:
+                        print(f"{RED}[ERROR]{RESET} Usage: auto config <param> <value>")
+                        continue
+                        
+                    param = parts[2]
+                    value_str = parts[3]
+                    
+                    # Convert the string value to the appropriate type
+                    config = protocol.get_auto_mode_config()
+                    if not hasattr(config, param):
+                        print(f"{RED}[ERROR]{RESET} Unknown parameter: {param}")
+                        print("Use 'auto config list' to see all available parameters")
+                        continue
+                        
+                    current_value = getattr(config, param)
+                    try:
+                        if isinstance(current_value, bool):
+                            if value_str.lower() in ("true", "yes", "on", "1"):
+                                value = True
+                            elif value_str.lower() in ("false", "no", "off", "0"):
+                                value = False
+                            else:
+                                raise ValueError(f"Boolean value must be true/false/yes/no/on/off/1/0")
+                        elif isinstance(current_value, int):
+                            value = int(value_str)
+                        elif isinstance(current_value, float):
+                            value = float(value_str)
+                        elif isinstance(current_value, str):
+                            value = value_str
+                        else:
+                            value = value_str  # Default to string
+                            
+                        protocol.configure_auto_mode(**{param: value})
+                        print(f"{GREEN}[AUTO]{RESET} Set {param} = {value}")
+                    
+                    except ValueError as e:
+                        print(f"{RED}[ERROR]{RESET} Invalid value for {param}: {e}")
+                
+                elif subcmd == "message":
+                    if len(parts) < 3:
+                        print(f"{RED}[ERROR]{RESET} Usage: auto message <text>")
+                        continue
+                    
+                    message = " ".join(parts[2:])
+                    protocol.queue_auto_message(message)
+                    print(f"{GREEN}[AUTO]{RESET} Message queued for sending: {message}")
+                
+                elif subcmd == "passive":
+                    # Configure as passive peer (responds but doesn't initiate)
+                    protocol.configure_auto_mode(
+                        ping_response_accept=True,
+                        ping_auto_initiate=False,
+                        active_mode=False
+                    )
+                    print(f"{GREEN}[AUTO]{RESET} Configured as passive peer")
+                
+                elif subcmd == "active":
+                    # Configure as active peer (initiates protocol)
+                    protocol.configure_auto_mode(
+                        ping_response_accept=True,
+                        ping_auto_initiate=True,
+                        active_mode=True
+                    )
+                    print(f"{GREEN}[AUTO]{RESET} Configured as active peer")
+                
+                else:
+                    print(f"{RED}[ERROR]{RESET} Unknown auto mode command: {subcmd}")
+                    print("Available commands: start, stop, status, config, message, passive, active")
+            
+            # Legacy commands
+            elif cmd == "auto_responder":
+                if len(parts) != 2:
+                    print(f"{RED}[ERROR]{RESET} Usage: auto_responder <on|off>")
+                    continue
+                val = parts[1].lower()
+                if val not in ("on", "off"):
+                    print(f"{RED}[ERROR]{RESET} Value must be 'on' or 'off'.")
+                    continue
+                protocol.enable_auto_responder(val == "on")
+                print(f"{YELLOW}[WARNING]{RESET} Using legacy auto responder. Consider using 'auto' commands instead.")
                 
-        elif cmd == "auto_responder":
-            if len(parts) != 2:
-                print(f"{RED}Usage: auto_responder <on|off>{RESET}")
-                continue
-            arg = parts[1].lower()
-            if arg == "on":
-                protocol.enable_auto_responder(True)
-            elif arg == "off":
-                protocol.enable_auto_responder(False)
             else:
-                print(f"{RED}Usage: auto_responder <on|off>{RESET}")
+                print(f"{RED}[ERROR]{RESET} Unknown command: {cmd}")
-
+                print("Type 'help' for a list of available commands.")
-        else:
-            print(f"{RED}[ERROR]{RESET} Unknown command: {cmd}")
                 
+        except Exception as e:
+            print(f"{RED}[ERROR]{RESET} Command failed: {e}")
 
 if __name__ == "__main__":
-    main()
+    try:
+        main()
+    except KeyboardInterrupt:
+        print("\nExiting...")
+    except Exception as e:
+        print(f"{RED}[FATAL ERROR]{RESET} {e}")
+        sys.exit(1)

protocol_prototype/crypto_utils.py

@@ -1,50 +1,78 @@
 import os
+from typing import Tuple
 from cryptography.exceptions import InvalidSignature
 from cryptography.hazmat.primitives import hashes, serialization
 from cryptography.hazmat.primitives.asymmetric import ec, utils
 from cryptography.hazmat.primitives.asymmetric.utils import decode_dss_signature, encode_dss_signature
 
-def generate_identity_keys():
+def generate_identity_keys() -> Tuple[ec.EllipticCurvePrivateKey, bytes]:
     """
     Generate an ECDSA (P-256) identity key pair.
-    Return (private_key, public_key_bytes).
+    
-    public_key_bytes is raw x||y each 32 bytes (uncompressed minus the 0x04 prefix).
+    Returns:
+        Tuple containing:
+        - private_key: EllipticCurvePrivateKey object
+        - public_key_bytes: Raw x||y format (64 bytes, 512 bits)
     """
     private_key = ec.generate_private_key(ec.SECP256R1())
     public_numbers = private_key.public_key().public_numbers()
 
     x_bytes = public_numbers.x.to_bytes(32, byteorder='big')
     y_bytes = public_numbers.y.to_bytes(32, byteorder='big')
-    pubkey_bytes = x_bytes + y_bytes  # 64 bytes
+    pubkey_bytes = x_bytes + y_bytes  # 64 bytes total
 
     return private_key, pubkey_bytes
 
 
-def load_peer_identity_key(pubkey_bytes: bytes):
+def load_peer_identity_key(pubkey_bytes: bytes) -> ec.EllipticCurvePublicKey:
     """
-    Given 64 bytes (x||y) for P-256, return a cryptography public key object.
+    Convert a raw public key (64 bytes, x||y format) to a cryptography public key object.
+    
+    Args:
+        pubkey_bytes: Raw 64-byte public key (x||y format)
+        
+    Returns:
+        EllipticCurvePublicKey object
+        
+    Raises:
+        ValueError: If the pubkey_bytes is not exactly 64 bytes
     """
     if len(pubkey_bytes) != 64:
         raise ValueError("Peer identity pubkey must be exactly 64 bytes (x||y).")
+        
     x_int = int.from_bytes(pubkey_bytes[:32], byteorder='big')
     y_int = int.from_bytes(pubkey_bytes[32:], byteorder='big')
+    
     public_numbers = ec.EllipticCurvePublicNumbers(x_int, y_int, ec.SECP256R1())
     return public_numbers.public_key()
 
 
-def sign_data(private_key, data: bytes) -> bytes:
+def sign_data(private_key: ec.EllipticCurvePrivateKey, data: bytes) -> bytes:
     """
-    Sign 'data' with ECDSA using P-256 private key.
+    Sign data with ECDSA using a P-256 private key.
-    Returns DER-encoded signature (variable length, up to ~70-72 bytes).
+    
+    Args:
+        private_key: EllipticCurvePrivateKey for signing
+        data: Bytes to sign
+        
+    Returns:
+        DER-encoded signature (variable length, up to ~70-72 bytes)
     """
     signature = private_key.sign(data, ec.ECDSA(hashes.SHA256()))
     return signature
 
 
-def verify_signature(public_key, signature: bytes, data: bytes) -> bool:
+def verify_signature(public_key: ec.EllipticCurvePublicKey, signature: bytes, data: bytes) -> bool:
     """
-    Verify DER-encoded ECDSA signature with the given public key.
+    Verify a DER-encoded ECDSA signature.
-    Return True if valid, False otherwise.
+    
+    Args:
+        public_key: EllipticCurvePublicKey for verification
+        signature: DER-encoded signature
+        data: Original signed data
+        
+    Returns:
+        True if signature is valid, False otherwise
     """
     try:
         public_key.verify(signature, data, ec.ECDSA(hashes.SHA256()))
@@ -53,35 +81,62 @@ def verify_signature(public_key, signature: bytes, data: bytes) -> bool:
         return False
 
 
-def get_ephemeral_keypair():
+def get_ephemeral_keypair() -> Tuple[ec.EllipticCurvePrivateKey, bytes]:
     """
-    Generate ephemeral ECDH keypair (P-256).
+    Generate an ephemeral ECDH key pair (P-256).
-    Return (private_key, pubkey_bytes).
+    
+    Returns:
+        Tuple containing:
+        - private_key: EllipticCurvePrivateKey object
+        - pubkey_bytes: Raw x||y format (64 bytes, 512 bits)
     """
     private_key = ec.generate_private_key(ec.SECP256R1())
     numbers = private_key.public_key().public_numbers()
+    
     x_bytes = numbers.x.to_bytes(32, 'big')
     y_bytes = numbers.y.to_bytes(32, 'big')
-    return private_key, x_bytes + y_bytes  # 64 bytes
+    
+    return private_key, x_bytes + y_bytes  # 64 bytes total
 
 
-def compute_ecdh_shared_key(private_key, peer_pubkey_bytes: bytes) -> bytes:
+def compute_ecdh_shared_key(private_key: ec.EllipticCurvePrivateKey, peer_pubkey_bytes: bytes) -> bytes:
     """
-    Given a local ECDH private_key and the peer's ephemeral pubkey (64 bytes),
+    Compute a shared secret using ECDH.
-    compute the shared secret.
+    
+    Args:
+        private_key: Local ECDH private key
+        peer_pubkey_bytes: Peer's ephemeral public key (64 bytes, raw x||y format)
+        
+    Returns:
+        Shared secret bytes
+        
+    Raises:
+        ValueError: If peer_pubkey_bytes is not 64 bytes
     """
+    if len(peer_pubkey_bytes) != 64:
+        raise ValueError("Peer public key must be 64 bytes (x||y format)")
+        
     x_int = int.from_bytes(peer_pubkey_bytes[:32], 'big')
     y_int = int.from_bytes(peer_pubkey_bytes[32:], 'big')
+    
+    # Create public key object from raw components
     peer_public_numbers = ec.EllipticCurvePublicNumbers(x_int, y_int, ec.SECP256R1())
     peer_public_key = peer_public_numbers.public_key()
+    
+    # Perform key exchange
     shared_key = private_key.exchange(ec.ECDH(), peer_public_key)
     return shared_key
 
 
 def der_to_raw(der_sig: bytes) -> bytes:
     """
-    Convert a DER-encoded ECDSA signature to a raw 64-byte signature (r||s),
+    Convert a DER-encoded ECDSA signature to a raw 64-byte signature (r||s).
-    where each component is padded to 32 bytes.
+    
+    Args:
+        der_sig: DER-encoded signature
+        
+    Returns:
+        Raw 64-byte signature (r||s format), with each component padded to 32 bytes
     """
     r, s = decode_dss_signature(der_sig)
     r_bytes = r.to_bytes(32, byteorder='big')
@@ -92,10 +147,19 @@ def der_to_raw(der_sig: bytes) -> bytes:
 def raw_signature_to_der(raw_sig: bytes) -> bytes:
     """
     Convert a raw signature (64 bytes, concatenated r||s) to DER-encoded signature.
+    
+    Args:
+        raw_sig: Raw 64-byte signature (r||s format)
+        
+    Returns:
+        DER-encoded signature
+        
+    Raises:
+        ValueError: If raw_sig is not 64 bytes
     """
     if len(raw_sig) != 64:
         raise ValueError("Raw signature must be 64 bytes (r||s).")
-    from cryptography.hazmat.primitives.asymmetric.utils import encode_dss_signature
+        
     r = int.from_bytes(raw_sig[:32], 'big')
     s = int.from_bytes(raw_sig[32:], 'big')
     return encode_dss_signature(r, s)

protocol_prototype/encryption.py

@@ -0,0 +1,263 @@
+import os
+import struct
+from typing import Optional, Tuple
+from cryptography.hazmat.primitives.ciphers.aead import AESGCM, ChaCha20Poly1305
+
+class MessageHeader:
+    """
+    Header of an encrypted message (18 bytes total):
+    
+    Clear Text Section (4 bytes):
+    - flag: 16 bits (0xBEEF by default)
+    - data_len: 16 bits (length of encrypted payload excluding tag)
+    
+    Associated Data (14 bytes):
+    - retry: 8 bits (retry counter)
+    - connection_status: 4 bits (e.g., CRC required) + 4 bits padding
+    - iv/messageID: 96 bits (12 bytes)
+    """
+    def __init__(self, flag: int, data_len: int, retry: int, connection_status: int, iv: bytes):
+        if not (0 <= flag < 65536):
+            raise ValueError("Flag must fit in 16 bits (0..65535)")
+        if not (0 <= data_len < 65536):
+            raise ValueError("Data length must fit in 16 bits (0..65535)")
+        if not (0 <= retry < 256):
+            raise ValueError("Retry must fit in 8 bits (0..255)")
+        if not (0 <= connection_status < 16):
+            raise ValueError("Connection status must fit in 4 bits (0..15)")
+        if len(iv) != 12:
+            raise ValueError("IV must be 12 bytes (96 bits)")
+            
+        self.flag = flag                  # 16 bits
+        self.data_len = data_len          # 16 bits
+        self.retry = retry                # 8 bits
+        self.connection_status = connection_status  # 4 bits
+        self.iv = iv                      # 96 bits (12 bytes)
+
+    def pack(self) -> bytes:
+        """Pack header into 18 bytes."""
+        # Pack flag and data_len (4 bytes)
+        header = struct.pack('>H H', self.flag, self.data_len)
+        
+        # Pack retry and connection_status (2 bytes)
+        # connection_status in high 4 bits of second byte, 4 bits padding as zero
+        ad_byte = (self.connection_status & 0x0F) << 4
+        ad_packed = struct.pack('>B B', self.retry, ad_byte)
+        
+        # Append IV (12 bytes)
+        return header + ad_packed + self.iv
+        
+    def get_associated_data(self) -> bytes:
+        """Get the associated data for AEAD encryption (retry, conn_status, iv)."""
+        # Pack retry and connection_status
+        ad_byte = (self.connection_status & 0x0F) << 4
+        ad_packed = struct.pack('>B B', self.retry, ad_byte)
+        
+        # Append IV
+        return ad_packed + self.iv
+        
+    @classmethod
+    def unpack(cls, data: bytes) -> 'MessageHeader':
+        """Unpack 18 bytes into a MessageHeader object."""
+        if len(data) < 18:
+            raise ValueError(f"Header data too short: {len(data)} bytes, expected 18")
+            
+        flag, data_len = struct.unpack('>H H', data[:4])
+        retry, ad_byte = struct.unpack('>B B', data[4:6])
+        connection_status = (ad_byte >> 4) & 0x0F
+        iv = data[6:18]
+        
+        return cls(flag, data_len, retry, connection_status, iv)
+
+class EncryptedMessage:
+    """
+    Encrypted message packet format:
+    
+    - Header (18 bytes):
+      * flag: 16 bits
+      * data_len: 16 bits
+      * retry: 8 bits
+      * connection_status: 4 bits (+ 4 bits padding)
+      * iv/messageID: 96 bits (12 bytes)
+    
+    - Payload: variable length encrypted data
+    
+    - Footer:
+      * Authentication tag: 128 bits (16 bytes)
+      * CRC32: 32 bits (4 bytes) - optional, based on connection_status
+    """
+    def __init__(self, plaintext: bytes, key: bytes, flag: int = 0xBEEF, 
+                 retry: int = 0, connection_status: int = 0, iv: bytes = None,
+                 cipher_type: int = 0):
+        self.plaintext = plaintext
+        self.key = key
+        self.flag = flag
+        self.retry = retry
+        self.connection_status = connection_status
+        self.iv = iv or generate_iv(initial=True)
+        self.cipher_type = cipher_type  # 0 = AES-256-GCM, 1 = ChaCha20-Poly1305
+        
+        # Will be set after encryption
+        self.ciphertext = None
+        self.tag = None
+        self.header = None
+        
+    def encrypt(self) -> bytes:
+        """Encrypt the plaintext and return the full encrypted message."""
+        # Create header with correct data_len (which will be set after encryption)
+        self.header = MessageHeader(
+            flag=self.flag,
+            data_len=0,  # Will be updated after encryption
+            retry=self.retry,
+            connection_status=self.connection_status,
+            iv=self.iv
+        )
+        
+        # Get associated data for AEAD
+        aad = self.header.get_associated_data()
+        
+        # Encrypt using the appropriate cipher
+        if self.cipher_type == 0:  # AES-256-GCM
+            cipher = AESGCM(self.key)
+            ciphertext_with_tag = cipher.encrypt(self.iv, self.plaintext, aad)
+        elif self.cipher_type == 1:  # ChaCha20-Poly1305
+            cipher = ChaCha20Poly1305(self.key)
+            ciphertext_with_tag = cipher.encrypt(self.iv, self.plaintext, aad)
+        else:
+            raise ValueError(f"Unsupported cipher type: {self.cipher_type}")
+        
+        # Extract ciphertext and tag
+        self.tag = ciphertext_with_tag[-16:]
+        self.ciphertext = ciphertext_with_tag[:-16]
+        
+        # Update header with actual data length
+        self.header.data_len = len(self.ciphertext)
+        
+        # Pack everything together
+        packed_header = self.header.pack()
+        
+        # Check if CRC is required (based on connection_status)
+        if self.connection_status & 0x01:  # Lowest bit indicates CRC required
+            import zlib
+            # Compute CRC32 of header + ciphertext + tag
+            crc = zlib.crc32(packed_header + self.ciphertext + self.tag) & 0xffffffff
+            crc_bytes = struct.pack('>I', crc)
+            return packed_header + self.ciphertext + self.tag + crc_bytes
+        else:
+            return packed_header + self.ciphertext + self.tag
+            
+    @classmethod
+    def decrypt(cls, data: bytes, key: bytes, cipher_type: int = 0) -> Tuple[bytes, MessageHeader]:
+        """
+        Decrypt an encrypted message and return the plaintext and header.
+        
+        Args:
+            data: The full encrypted message
+            key: The encryption key
+            cipher_type: 0 for AES-256-GCM, 1 for ChaCha20-Poly1305
+            
+        Returns:
+            Tuple of (plaintext, header)
+        """
+        if len(data) < 18 + 16:  # Header + minimum tag size
+            raise ValueError("Message too short")
+            
+        # Extract header
+        header_bytes = data[:18]
+        header = MessageHeader.unpack(header_bytes)
+        
+        # Get ciphertext and tag
+        data_len = header.data_len
+        ciphertext_start = 18
+        ciphertext_end = ciphertext_start + data_len
+        
+        if ciphertext_end + 16 > len(data):
+            raise ValueError("Message length does not match header's data_len")
+            
+        ciphertext = data[ciphertext_start:ciphertext_end]
+        tag = data[ciphertext_end:ciphertext_end + 16]
+        
+        # Get associated data for AEAD
+        aad = header.get_associated_data()
+        
+        # Combine ciphertext and tag for decryption
+        ciphertext_with_tag = ciphertext + tag
+        
+        # Decrypt using the appropriate cipher
+        try:
+            if cipher_type == 0:  # AES-256-GCM
+                cipher = AESGCM(key)
+                plaintext = cipher.decrypt(header.iv, ciphertext_with_tag, aad)
+            elif cipher_type == 1:  # ChaCha20-Poly1305
+                cipher = ChaCha20Poly1305(key)
+                plaintext = cipher.decrypt(header.iv, ciphertext_with_tag, aad)
+            else:
+                raise ValueError(f"Unsupported cipher type: {cipher_type}")
+                
+            return plaintext, header
+        except Exception as e:
+            raise ValueError(f"Decryption failed: {e}")
+
+def generate_iv(initial: bool = False, previous_iv: bytes = None) -> bytes:
+    """
+    Generate a 96-bit IV (12 bytes).
+    
+    Args:
+        initial: If True, return a random IV
+        previous_iv: The previous IV to increment
+        
+    Returns:
+        A new IV
+    """
+    if initial or previous_iv is None:
+        return os.urandom(12)  # 96 bits
+    else:
+        # Increment the previous IV by 1 modulo 2^96
+        iv_int = int.from_bytes(previous_iv, 'big')
+        iv_int = (iv_int + 1) % (1 << 96)
+        return iv_int.to_bytes(12, 'big')
+
+# Convenience functions to match original API
+def encrypt_message(plaintext: bytes, key: bytes, flag: int = 0xBEEF, 
+                   retry: int = 0, connection_status: int = 0, 
+                   iv: bytes = None, cipher_type: int = 0) -> bytes:
+    """
+    Encrypt a message using the specified parameters.
+    
+    Args:
+        plaintext: The data to encrypt
+        key: The encryption key (32 bytes for AES-256-GCM, 32 bytes for ChaCha20-Poly1305)
+        flag: 16-bit flag value (default: 0xBEEF)
+        retry: 8-bit retry counter
+        connection_status: 4-bit connection status
+        iv: Optional 96-bit IV (if None, a random one will be generated)
+        cipher_type: 0 for AES-256-GCM, 1 for ChaCha20-Poly1305
+        
+    Returns:
+        The full encrypted message
+    """
+    message = EncryptedMessage(
+        plaintext=plaintext,
+        key=key,
+        flag=flag,
+        retry=retry,
+        connection_status=connection_status,
+        iv=iv,
+        cipher_type=cipher_type
+    )
+    return message.encrypt()
+
+def decrypt_message(message: bytes, key: bytes, cipher_type: int = 0) -> bytes:
+    """
+    Decrypt a message.
+    
+    Args:
+        message: The full encrypted message
+        key: The encryption key
+        cipher_type: 0 for AES-256-GCM, 1 for ChaCha20-Poly1305
+        
+    Returns:
+        The decrypted plaintext
+    """
+    plaintext, _ = EncryptedMessage.decrypt(message, key, cipher_type)
+    return plaintext

protocol_prototype/main.py

@@ -1,16 +0,0 @@
-# This is a sample Python script.
-
-# Press Shift+F10 to execute it or replace it with your code.
-# Press Double Shift to search everywhere for classes, files, tool windows, actions, and settings.
-
-
-def print_hi(name):
-    # Use a breakpoint in the code line below to debug your script.
-    print(f'Hi, {name}')  # Press Ctrl+F8 to toggle the breakpoint.
-
-
-# Press the green button in the gutter to run the script.
-if __name__ == '__main__':
-    print_hi('PyCharm')
-
-# See PyCharm help at https://www.jetbrains.com/help/pycharm/

protocol_prototype/messages.py

@@ -3,6 +3,7 @@ import struct
 import time
 import zlib
 import hashlib
+from typing import Tuple, Optional
 
 def crc32_of(data: bytes) -> int:
     """
@@ -11,144 +12,163 @@ def crc32_of(data: bytes) -> int:
     return zlib.crc32(data) & 0xffffffff
 
 
-# =============================================================================
+# ---------------------------------------------------------------------------
-# 1) Ping Request (295 bits)
+# PING REQUEST (new format)
-#    - 256-bit nonce
+# Fields (in order):
-#    - 7-bit version
+#   - session_nonce: 129 bits (from the top 129 bits of 17 random bytes)
-#    - 32-bit CRC
+#   - version: 7 bits
-#    = 295 bits total
+#   - cipher: 4 bits   (0 = AES-256-GCM, 1 = ChaCha20-poly1305; for now only 0 is used)
-#    In practice, we store 37 bytes (296 bits); 1 bit is unused.
+#   - CRC: 32 bits
-# =============================================================================
+#
-
+# Total bits: 129 + 7 + 4 + 32 = 172 bits. We pack into 22 bytes (176 bits) with 4 spare bits.
-def build_ping_request(version: int) -> bytes:
+# ---------------------------------------------------------------------------
+class PingRequest:
     """
-    Build a Ping request with:
+    PING REQUEST format (172 bits / 22 bytes):
-      - 256-bit nonce (32 bytes)
+    - session_nonce: 129 bits (from top 129 bits of 17 random bytes)
-      - 7-bit version
+    - version: 7 bits
-      - 32-bit CRC
+    - cipher: 4 bits (0 = AES-256-GCM, 1 = ChaCha20-poly1305)
-    We do bit-packing. The final result is 37 bytes (296 bits), with 1 unused bit.
+    - CRC: 32 bits
     """
-    if not (0 <= version < 128):
+    def __init__(self, version: int, cipher: int, session_nonce: bytes = None):
-        raise ValueError("Version must fit in 7 bits (0..127)")
+        if not (0 <= version < 128):
+            raise ValueError("Version must fit in 7 bits (0..127)")
+        if not (0 <= cipher < 16):
+            raise ValueError("Cipher must fit in 4 bits (0..15)")
         
-    # 1) Generate 256-bit nonce
+        self.version = version
-    nonce = os.urandom(32)  # 32 bytes = 256 bits
+        self.cipher = cipher
         
-    # We'll build partial_data = [nonce (256 bits), version (7 bits)] as an integer
+        # Generate session nonce if not provided
-    # Then compute CRC-32 over those bytes, then append 32 bits of CRC.
+        if session_nonce is None:
-    partial_int = int.from_bytes(nonce, 'big') << 7  # shift left 7 bits
+            # Generate 17 random bytes
-    partial_int |= version  # put version in the low 7 bits
+            nonce_full = os.urandom(17)
+            # Use top 129 bits
+            nonce_int_full = int.from_bytes(nonce_full, 'big')
+            nonce_129_int = nonce_int_full >> 7  # drop lowest 7 bits
+            self.session_nonce = nonce_129_int.to_bytes(17, 'big')
+        else:
+            if len(session_nonce) != 17:
+                raise ValueError("Session nonce must be 17 bytes (136 bits)")
+            self.session_nonce = session_nonce
     
-    # Convert partial to bytes
+    def serialize(self) -> bytes:
-    # partial is 256+7=263 bits => needs 33 bytes to store
+        """Serialize the ping request into a 22-byte packet."""
-    partial_bytes = partial_int.to_bytes(33, 'big')
+        # Convert session_nonce to integer (129 bits)
+        nonce_int = int.from_bytes(self.session_nonce, 'big')
         
-    # Compute CRC over partial_bytes
+        # Pack fields: shift nonce left by 11 bits, add version and cipher
-    cval = crc32_of(partial_bytes)
+        partial_int = (nonce_int << 11) | (self.version << 4) | (self.cipher & 0x0F)
+        # This creates 129+7+4 = 140 bits; pack into 18 bytes
+        partial_bytes = partial_int.to_bytes(18, 'big')
         
-    # Now combine partial_data (263 bits) with 32 bits of CRC => 295 bits
+        # Compute CRC over these 18 bytes
-    # We'll store that in a single integer
+        cval = crc32_of(partial_bytes)
-    final_int = (int.from_bytes(partial_bytes, 'big') << 32) | cval
+        
-    # final_int is 263+32=295 bits, needs 37 bytes to store (the last bit is unused).
+        # Combine partial data with 32-bit CRC
-    final_bytes = final_int.to_bytes(37, 'big')
+        final_int = (int.from_bytes(partial_bytes, 'big') << 32) | cval
-    return final_bytes
+        return final_int.to_bytes(22, 'big')
+    
+    @classmethod
+    def deserialize(cls, data: bytes) -> Optional['PingRequest']:
+        """Deserialize a 22-byte packet into a PingRequest object."""
+        if len(data) != 22:
+            return None
+            
+        # Extract 176-bit integer
+        final_int = int.from_bytes(data, 'big')
+        
+        # Extract CRC and verify
+        crc_in = final_int & 0xffffffff
+        partial_int = final_int >> 32  # 140 bits
+        partial_bytes = partial_int.to_bytes(18, 'big')
+        crc_calc = crc32_of(partial_bytes)
+        
+        if crc_calc != crc_in:
+            return None
+            
+        # Extract fields
+        cipher = partial_int & 0x0F
+        version = (partial_int >> 4) & 0x7F
+        nonce_129_int = partial_int >> 11  # 129 bits
+        session_nonce = nonce_129_int.to_bytes(17, 'big')
+        
+        return cls(version, cipher, session_nonce)
 
 
-def parse_ping_request(data: bytes):
+
+# ---------------------------------------------------------------------------
+# PING RESPONSE (new format)
+# Fields:
+#   - timestamp: 32 bits (we take the lower 32 bits of the time in ms)
+#   - version: 7 bits
+#   - cipher: 4 bits
+#   - answer: 1 bit
+#   - CRC: 32 bits
+#
+# Total bits: 32 + 7 + 4 + 1 + 32 = 76 bits; pack into 10 bytes (80 bits) with 4 spare bits.
+# ---------------------------------------------------------------------------
+class PingResponse:
     """
-    Parse a Ping request (37 bytes = 295 bits).
+    PING RESPONSE format (76 bits / 10 bytes):
-    Returns (nonce, version) or None if invalid.
+    - timestamp: 32 bits (milliseconds since epoch, lower 32 bits)
+    - version: 7 bits
+    - cipher: 4 bits
+    - answer: 1 bit (0 = no, 1 = yes)
+    - CRC: 32 bits
     """
-    if len(data) != 37:
+    def __init__(self, version: int, cipher: int, answer: int, timestamp: int = None):
-        return None
+        if not (0 <= version < 128):
+            raise ValueError("Version must fit in 7 bits")
+        if not (0 <= cipher < 16):
+            raise ValueError("Cipher must fit in 4 bits")
+        if answer not in (0, 1):
+            raise ValueError("Answer must be 0 or 1")
             
-    # Convert to int
+        self.version = version
-    val_295 = int.from_bytes(data, 'big')  # 295 bits in a 37-byte integer
+        self.cipher = cipher
-    # Extract CRC (lowest 32 bits)
+        self.answer = answer
-    crc_in = val_295 & 0xffffffff
+        self.timestamp = timestamp or (int(time.time() * 1000) & 0xffffffff)
-    # Then shift right 32 bits to get partial_data
-    partial_val = val_295 >> 32  # 263 bits
     
-    # Convert partial_val back to bytes
+    def serialize(self) -> bytes:
-    partial_bytes = partial_val.to_bytes(33, 'big')
+        """Serialize the ping response into a 10-byte packet."""
+        # Pack timestamp, version, cipher, answer: 32+7+4+1 = 44 bits
+        partial_val = (self.timestamp << (7+4+1)) | (self.version << (4+1)) | (self.cipher << 1) | self.answer
+        partial_bytes = partial_val.to_bytes(6, 'big')  # 6 bytes = 48 bits, 4 spare bits
         
-    # Recompute CRC
+        # Compute CRC
-    crc_calc = crc32_of(partial_bytes)
+        cval = crc32_of(partial_bytes)
-    if crc_calc != crc_in:
-        return None
         
-    # Now parse out nonce (256 bits) and version (7 bits)
+        # Combine with CRC
-    # partial_val is 263 bits
+        final_val = (int.from_bytes(partial_bytes, 'big') << 32) | cval
-    version = partial_val & 0x7f  # low 7 bits
+        return final_val.to_bytes(10, 'big')
-    nonce_val = partial_val >> 7  # high 256 bits
-    nonce_bytes = nonce_val.to_bytes(32, 'big')
     
-    return (nonce_bytes, version)
+    @classmethod
+    def deserialize(cls, data: bytes) -> Optional['PingResponse']:
+        """Deserialize a 10-byte packet into a PingResponse object."""
+        if len(data) != 10:
+            return None
             
+        # Extract 80-bit integer
+        final_int = int.from_bytes(data, 'big')
         
-# =============================================================================
+        # Extract CRC and verify
-# 2) Ping Response (72 bits)
+        crc_in = final_int & 0xffffffff
-#    - 32-bit timestamp
+        partial_int = final_int >> 32  # 48 bits
-#    - 7-bit version + 1-bit answer => 8 bits
+        partial_bytes = partial_int.to_bytes(6, 'big')
-#    - 32-bit CRC
+        crc_calc = crc32_of(partial_bytes)
-#    = 72 bits total => 9 bytes
-# =============================================================================
         
-def build_ping_response(version: int, answer: int) -> bytes:
+        if crc_calc != crc_in:
-    """
+            return None
-    Build a Ping response:
-      - 32-bit timestamp (lowest 32 bits of current time in ms)
-      - 7-bit version + 1-bit answer
-      - 32-bit CRC
-    => 72 bits = 9 bytes
-    """
-    if not (0 <= version < 128):
-        raise ValueError("Version must fit in 7 bits.")
-    if answer not in (0, 1):
-        raise ValueError("Answer must be 0 or 1.")
             
-    # 32-bit timestamp = current time in ms, truncated to 32 bits
+        # Extract fields (discard 4 spare bits)
-    t_ms = int(time.time() * 1000) & 0xffffffff
+        partial_int >>= 4  # now 44 bits
+        answer = partial_int & 0x01
+        cipher = (partial_int >> 1) & 0x0F
+        version = (partial_int >> (1+4)) & 0x7F
+        timestamp = partial_int >> (1+4+7)
         
-    # partial = [timestamp (32 bits), version (7 bits), answer (1 bit)] => 40 bits
+        return cls(version, cipher, answer, timestamp)
-    partial_val = (t_ms << 8) | ((version << 1) & 0xfe) | (answer & 0x01)
-    # partial_val is 40 bits => 5 bytes
-    partial_bytes = partial_val.to_bytes(5, 'big')
-
-    # CRC over these 5 bytes
-    cval = crc32_of(partial_bytes)
-
-    # Combine partial (40 bits) with 32 bits of CRC => 72 bits total
-    final_val = (int.from_bytes(partial_bytes, 'big') << 32) | cval
-    final_bytes = final_val.to_bytes(9, 'big')
-    return final_bytes
-
-
-def parse_ping_response(data: bytes):
-    """
-    Parse a Ping response (72 bits = 9 bytes).
-    Return (timestamp_ms, version, answer) or None if invalid.
-    """
-    if len(data) != 9:
-        return None
-
-    val_72 = int.from_bytes(data, 'big')  # 72 bits
-    crc_in = val_72 & 0xffffffff
-    partial_val = val_72 >> 32  # 40 bits
-
-    partial_bytes = partial_val.to_bytes(5, 'big')
-    crc_calc = crc32_of(partial_bytes)
-    if crc_calc != crc_in:
-        return None
-
-    # Now parse partial_val
-    # partial_val = [timestamp(32 bits), version(7 bits), answer(1 bit)]
-    t_ms = (partial_val >> 8) & 0xffffffff
-    va = partial_val & 0xff  # 8 bits = [7 bits version, 1 bit answer]
-    version = (va >> 1) & 0x7f
-    answer = va & 0x01
-
-    return (t_ms, version, answer)
 
 
 # =============================================================================
@@ -161,53 +181,60 @@ def parse_ping_response(data: bytes):
 #    => total 4 + 64 + 64 + 32 + 4 = 168 bytes = 1344 bits
 # =============================================================================
 
-def build_handshake_message(timestamp: int,
+class Handshake:
-                            ephemeral_pubkey: bytes,
-                            ephemeral_signature: bytes,
-                            pfs_hash: bytes) -> bytes:
     """
-    Build handshake:
+    HANDSHAKE format (1344 bits / 168 bytes):
-      - 4 bytes: timestamp
+    - timestamp: 32 bits
-      - 64 bytes: ephemeral_pubkey (x||y, raw)
+    - ephemeral_pubkey: 512 bits (64 bytes, raw x||y format)
-      - 64 bytes: ephemeral_signature (r||s, raw)
+    - ephemeral_signature: 512 bits (64 bytes, raw r||s format)
-      - 32 bytes: pfs_hash
+    - pfs_hash: 256 bits (32 bytes)
-      - 4 bytes: CRC-32
+    - CRC: 32 bits
-    => 168 bytes total
     """
-    if len(ephemeral_pubkey) != 64:
+    def __init__(self, ephemeral_pubkey: bytes, ephemeral_signature: bytes, pfs_hash: bytes, timestamp: int = None):
-        raise ValueError("ephemeral_pubkey must be 64 bytes (raw x||y).")
+        if len(ephemeral_pubkey) != 64:
-    if len(ephemeral_signature) != 64:
+            raise ValueError("ephemeral_pubkey must be 64 bytes (raw x||y)")
-        raise ValueError("ephemeral_signature must be 64 bytes (raw r||s).")
+        if len(ephemeral_signature) != 64:
-    if len(pfs_hash) != 32:
+            raise ValueError("ephemeral_signature must be 64 bytes (raw r||s)")
-        raise ValueError("pfs_hash must be 32 bytes.")
+        if len(pfs_hash) != 32:
+            raise ValueError("pfs_hash must be 32 bytes")
             
-    partial = struct.pack("!I", timestamp) \
+        self.ephemeral_pubkey = ephemeral_pubkey
-              + ephemeral_pubkey \
+        self.ephemeral_signature = ephemeral_signature
-              + ephemeral_signature \
+        self.pfs_hash = pfs_hash
-              + pfs_hash
+        self.timestamp = timestamp or (int(time.time() * 1000) & 0xffffffff)
-    cval = crc32_of(partial)
-    return partial + struct.pack("!I", cval)
     
+    def serialize(self) -> bytes:
+        """Serialize the handshake into a 168-byte packet."""
+        # Pack timestamp and other fields
+        partial = struct.pack("!I", self.timestamp) + self.ephemeral_pubkey + self.ephemeral_signature + self.pfs_hash
         
-def parse_handshake_message(data: bytes):
+        # Compute CRC
-    """
+        cval = crc32_of(partial)
-    Parse handshake message (168 bytes).
-    Return (timestamp, ephemeral_pub, ephemeral_sig, pfs_hash) or None if invalid.
-    """
-    if len(data) != 168:
-        return None
-    partial = data[:-4]   # first 164 bytes
-    crc_in = struct.unpack("!I", data[-4:])[0]
-    crc_calc = crc32_of(partial)
-    if crc_calc != crc_in:
-        return None
         
-    # Now parse fields
+        # Append CRC
-    timestamp = struct.unpack("!I", partial[:4])[0]
+        return partial + struct.pack("!I", cval)
-    ephemeral_pub = partial[4:4+64]
+    
-    ephemeral_sig = partial[68:68+64]
+    @classmethod
-    pfs_hash = partial[132:132+32]
+    def deserialize(cls, data: bytes) -> Optional['Handshake']:
-    return (timestamp, ephemeral_pub, ephemeral_sig, pfs_hash)
+        """Deserialize a 168-byte packet into a Handshake object."""
+        if len(data) != 168:
+            return None
+            
+        # Extract and verify CRC
+        partial = data[:-4]
+        crc_in = struct.unpack("!I", data[-4:])[0]
+        crc_calc = crc32_of(partial)
+        
+        if crc_calc != crc_in:
+            return None
+            
+        # Extract fields
+        timestamp = struct.unpack("!I", partial[:4])[0]
+        ephemeral_pubkey = partial[4:4+64]
+        ephemeral_signature = partial[68:68+64]
+        pfs_hash = partial[132:132+32]
+        
+        return cls(ephemeral_pubkey, ephemeral_signature, pfs_hash, timestamp)
 
 
 # =============================================================================
@@ -218,15 +245,18 @@ def parse_handshake_message(data: bytes):
 
 def compute_pfs_hash(session_number: int, shared_secret_hex: str) -> bytes:
     """
-    Return 32 bytes (256 bits) for the PFS field.
+    Compute the PFS hash field for handshake messages:
-    If session_number < 0 => means no previous session => 32 zero bytes.
+    - If no previous session (session_number < 0), return 32 zero bytes
-    Otherwise => sha256( session_number (4 bytes) || shared_secret ).
+    - Otherwise, compute sha256(session_number || shared_secret)
     """
     if session_number < 0:
         return b"\x00" * 32
 
     # Convert shared_secret_hex to raw bytes
     secret_bytes = bytes.fromhex(shared_secret_hex)
+    
     # Pack session_number as 4 bytes
     sn_bytes = struct.pack("!I", session_number)
+    
+    # Compute hash
     return hashlib.sha256(sn_bytes + secret_bytes).digest()

protocol_prototype/protocol.py

@@ -1,8 +1,8 @@
 import random
+import os
 import time
 import threading
-from typing import List, Dict, Any
+from typing import List, Dict, Any, Optional, Tuple
-from crypto_utils import raw_signature_to_der
 
 from crypto_utils import (
     generate_identity_keys,
@@ -10,15 +10,20 @@ from crypto_utils import (
     sign_data,
     verify_signature,
     get_ephemeral_keypair,
-    compute_ecdh_shared_key
+    compute_ecdh_shared_key,
+    der_to_raw,
+    raw_signature_to_der
 )
 from messages import (
-    build_ping_request, parse_ping_request,
+    PingRequest, PingResponse, Handshake,
-    build_ping_response, parse_ping_response,
-    build_handshake_message, parse_handshake_message,
     compute_pfs_hash
 )
 import transmission
+from encryption import (
+    EncryptedMessage, MessageHeader,
+    generate_iv, encrypt_message, decrypt_message
+)
+from auto_mode import AutoMode, AutoModeConfig
 
 # ANSI colors
 RED = "\033[91m"
@@ -30,44 +35,56 @@ RESET = "\033[0m"
 
 class IcingProtocol:
     def __init__(self):
-        # Identity keys
+        # Identity keys (each 512 bits when printed as hex of 64 bytes)
         self.identity_privkey, self.identity_pubkey = generate_identity_keys()
 
-        # Peer identity
+        # Peer identity for verifying ephemeral signatures
         self.peer_identity_pubkey_obj = None
         self.peer_identity_pubkey_bytes = None
 
-        # Ephemeral keys
+        # Ephemeral keys (our side)
         self.ephemeral_privkey = None
         self.ephemeral_pubkey = None
 
-        # Last computed shared secret (hex)
+        # Last computed shared secret (hex string)
         self.shared_secret = None
 
-        # For PFS: track session_number + last_shared_secret per peer identity
+        # Derived HKDF key (hex string, 256 bits)
-        # Key: bytes(64) peer identity pubkey
+        self.hkdf_key = None
-        # Value: (int session_number, str last_shared_secret_hex)
-        self.pfs_history: Dict[bytes, (int, str)] = {}
         
-        # Inbound messages are stored for manual or auto handling
+        # Negotiated cipher (0 = AES-256-GCM, 1 = ChaCha20-Poly1305)
-        # Each entry: { 'type': str, 'raw': bytes, 'parsed': Any, 'connection': PeerConnection }
+        self.cipher_type = 0
-        self.inbound_messages: List[Dict[str, Any]] = []
 
-        # Simple dictionary to track protocol flags
+        # For PFS: track per-peer session info (session number and last shared secret)
+        self.pfs_history: Dict[bytes, Tuple[int, str]] = {}
+
+        # Protocol flags
         self.state = {
             "ping_sent": False,
             "ping_received": False,
             "handshake_sent": False,
             "handshake_received": False,
+            "key_exchange_complete": False
         }
 
-        # Auto-responder toggle
+        # Auto mode for automated protocol operation
+        self.auto_mode = AutoMode(self)
+        
+        # Legacy auto-responder toggle (kept for backward compatibility)
         self.auto_responder = False
 
-        # Connections
+        # Active connections list
         self.connections = []
 
-        # Listening port
+        # Inbound messages (each message is a dict with keys: type, raw, parsed, connection)
+        self.inbound_messages: List[Dict[str, Any]] = []
+
+        # Store the session nonce (17 bytes but only 129 bits are valid) from first sent or received PING
+        self.session_nonce: bytes = None
+        
+        # Last used IV for encrypted messages
+        self.last_iv: bytes = None
+
         self.local_port = random.randint(30000, 40000)
         self.server_listener = transmission.ServerListener(
             host="127.0.0.1",
@@ -85,81 +102,127 @@ class IcingProtocol:
         print(f"{GREEN}[IcingProtocol]{RESET} New incoming connection.")
         self.connections.append(conn)
         
-    def on_data_received(self, conn: transmission.PeerConnection, data: bytes):
+        # Notify auto mode
-        """
+        self.auto_mode.handle_connection_established()
-        Called whenever data arrives on any open PeerConnection.
-        We'll parse and store the message, then handle automatically if auto_responder is on.
-        """
-        # Print data size in bits, not bytes
-        bits_count = len(data)*8
-        print(f"{GREEN}[RECV]{RESET} {bits_count} bits from peer: {data.hex()[:60]}{'...' if len(data.hex())>60 else ''}")
 
-        # Attempt to parse Ping request
+    def on_data_received(self, conn: transmission.PeerConnection, data: bytes):
-        if len(data) == 37:
+        bits_count = len(data) * 8
-            parsed = parse_ping_request(data)
+        print(
-            if parsed:
+            f"{GREEN}[RECV]{RESET} {bits_count} bits from peer: {data.hex()[:60]}{'...' if len(data.hex()) > 60 else ''}")
-                nonce, version = parsed
+
+        # PING REQUEST (22 bytes)
+        if len(data) == 22:
+            ping_request = PingRequest.deserialize(data)
+            if ping_request:
                 self.state["ping_received"] = True
+                
+                # If received cipher is not supported, force to 0 (AES-256-GCM)
+                if ping_request.cipher != 0 and ping_request.cipher != 1:
+                    print(f"{YELLOW}[NOTICE]{RESET} Received PING with unsupported cipher ({ping_request.cipher}); forcing cipher to 0 in response.")
+                    ping_request.cipher = 0
+                
+                # Store cipher type for future encrypted messages
+                self.cipher_type = ping_request.cipher
+                    
+                # Store session nonce if not already set
+                if self.session_nonce is None:
+                    self.session_nonce = ping_request.session_nonce
+                    print(f"{YELLOW}[NOTICE]{RESET} Stored session nonce from received PING.")
+                
                 index = len(self.inbound_messages)
                 msg = {
                     "type": "PING_REQUEST",
                     "raw": data,
-                    "parsed": {"nonce": nonce, "version": version},
+                    "parsed": ping_request,
                     "connection": conn
                 }
                 self.inbound_messages.append(msg)
-                print(f"{YELLOW}[NOTICE]{RESET} Stored inbound PING request (nonce={nonce.hex()}) at index={index}.")
                 
-                if self.auto_responder:
+                # Handle in auto mode (if active)
-                    # Schedule an automatic response after 2 seconds
+                self.auto_mode.handle_ping_received(index)
-                    threading.Timer(2.0, self._auto_respond_ping, args=(index,)).start()
                 
+                # Legacy auto-responder (for backward compatibility)
+                if self.auto_responder and not self.auto_mode.active:
+                    timer = threading.Timer(2.0, self._auto_respond_ping, args=[index])
+                    timer.daemon = True
+                    timer.start()
                 return
 
-        # Attempt to parse Ping response
+        # PING RESPONSE (10 bytes)
-        if len(data) == 9:
+        elif len(data) == 10:
-            parsed = parse_ping_response(data)
+            ping_response = PingResponse.deserialize(data)
-            if parsed:
+            if ping_response:
-                ts, version, answer_code = parsed
+                # Store negotiated cipher type
+                self.cipher_type = ping_response.cipher
+                
                 index = len(self.inbound_messages)
                 msg = {
                     "type": "PING_RESPONSE",
                     "raw": data,
-                    "parsed": {"timestamp": ts, "version": version, "answer_code": answer_code},
+                    "parsed": ping_response,
                     "connection": conn
                 }
                 self.inbound_messages.append(msg)
-                print(f"{YELLOW}[NOTICE]{RESET} Stored inbound PING response (answer_code={answer_code}) at index={index}.")
+                
+                # Notify auto mode (if active)
+                self.auto_mode.handle_ping_response_received(ping_response.answer == 1)
                 return
 
-        # Attempt to parse handshake
+        # HANDSHAKE message (168 bytes)
-        if len(data) == 168:
+        elif len(data) == 168:
-            parsed = parse_handshake_message(data)
+            handshake = Handshake.deserialize(data)
-            if parsed:
+            if handshake:
-                ts, ephemeral_pub, ephemeral_sig, pfs_hash = parsed
                 self.state["handshake_received"] = True
                 index = len(self.inbound_messages)
                 msg = {
                     "type": "HANDSHAKE",
                     "raw": data,
-                    "parsed": {
+                    "parsed": handshake,
-                        "ephemeral_pub": ephemeral_pub,
-                        "ephemeral_sig": ephemeral_sig,
-                        "timestamp": ts,
-                        "pfs hash": pfs_hash
-                    },
                     "connection": conn
                 }
                 self.inbound_messages.append(msg)
-                print(f"{YELLOW}[NOTICE]{RESET} Stored inbound HANDSHAKE at index={index}. ephemeral_pub={ephemeral_pub.hex()[:20]}...")
                 
-                if self.auto_responder:
+                # Notify auto mode (if active)
-                    # Schedule an automatic handshake "response" after 2 seconds
+                self.auto_mode.handle_handshake_received(index)
-                    threading.Timer(2.0, self._auto_respond_handshake, args=(index,)).start()
                 
+                # Legacy auto-responder
+                if self.auto_responder and not self.auto_mode.active:
+                    timer = threading.Timer(2.0, self._auto_respond_handshake, args=[index])
+                    timer.daemon = True
+                    timer.start()
                 return
 
-        # Otherwise, unrecognized
+        # Check if the message might be an encrypted message (e.g. header of 18 bytes at start)
+        elif len(data) >= 18:
+            # Try to parse header
+            try:
+                header = MessageHeader.unpack(data[:18])
+                # If header unpacking is successful and data length matches header expectations
+                expected_len = 18 + header.data_len + 16  # Header + payload + tag
+                
+                # Check if CRC is included
+                has_crc = (header.connection_status & 0x01) != 0
+                if has_crc:
+                    expected_len += 4  # Add CRC32 length
+                    
+                if len(data) >= expected_len:
+                    index = len(self.inbound_messages)
+                    msg = {
+                        "type": "ENCRYPTED_MESSAGE",
+                        "raw": data,
+                        "parsed": header,
+                        "connection": conn
+                    }
+                    self.inbound_messages.append(msg)
+                    print(f"{YELLOW}[NOTICE]{RESET} Stored inbound ENCRYPTED_MESSAGE at index={index}.")
+                    
+                    # Notify auto mode
+                    self.auto_mode.handle_encrypted_received(index)
+                    return
+            except Exception as e:
+                print(f"{RED}[ERROR]{RESET} Failed to parse message header: {e}")
+
+        # Otherwise, unrecognized/malformed message.
         index = len(self.inbound_messages)
         msg = {
             "type": "UNKNOWN",
@@ -170,8 +233,68 @@ class IcingProtocol:
         self.inbound_messages.append(msg)
         print(f"{RED}[WARNING]{RESET} Unrecognized or malformed message stored at index={index}.")
 
+
     # -------------------------------------------------------------------------
-    # Auto-responder helpers
+    # HKDF Derivation
+    # -------------------------------------------------------------------------
+
+    def derive_hkdf(self):
+        """
+        Derives a 256-bit key using HKDF.
+        Uses as input keying material (IKM) the shared secret from ECDH.
+        The salt is computed as SHA256(session_nonce || pfs_param), where:
+          - session_nonce is taken from self.session_nonce (17 bytes, 129 bits) or defaults to zeros.
+          - pfs_param is taken from the first inbound HANDSHAKE's pfs_hash field (32 bytes) or zeros.
+        """
+        if not self.shared_secret:
+            print(f"{RED}[ERROR]{RESET} No shared secret available; cannot derive HKDF key.")
+            return
+
+        # IKM: shared secret converted from hex to bytes.
+        ikm = bytes.fromhex(self.shared_secret)
+        # Use stored session_nonce if available; otherwise default to zeros.
+        session_nonce = self.session_nonce if self.session_nonce is not None else (b"\x00" * 17)
+
+        # Determine pfs_param from first HANDSHAKE message (if any)
+        pfs_param = None
+        for msg in self.inbound_messages:
+            if msg["type"] == "HANDSHAKE":
+                try:
+                    handshake = msg["parsed"]
+                    pfs_param = handshake.pfs_hash
+                except Exception:
+                    pfs_param = None
+                break
+        if pfs_param is None:
+            print(f"{RED}[WARNING]{RESET} No HANDSHAKE found; using 32 zero bytes for pfs_param.")
+            pfs_param = b"\x00" * 32  # 256-bit zeros
+
+        # Ensure both are bytes
+        if isinstance(session_nonce, str):
+            session_nonce = session_nonce.encode()
+        if isinstance(pfs_param, str):
+            pfs_param = pfs_param.encode()
+
+        from cryptography.hazmat.primitives import hashes
+        from cryptography.hazmat.primitives.kdf.hkdf import HKDF
+        hasher = hashes.Hash(hashes.SHA256())
+        hasher.update(session_nonce + pfs_param)
+        salt_value = hasher.finalize()
+
+        hkdf = HKDF(
+            algorithm=hashes.SHA256(),
+            length=32,  # 256 bits
+            salt=salt_value,
+            info=b"",
+        )
+        derived_key = hkdf.derive(ikm)
+        self.hkdf_key = derived_key.hex()
+        self.state["key_exchange_complete"] = True
+        print(f"{GREEN}[HKDF]{RESET} Derived HKDF key: {self.hkdf_key}")
+        return True
+
+    # -------------------------------------------------------------------------
+    # Legacy Auto-responder helpers (kept for backward compatibility)
     # -------------------------------------------------------------------------
 
     def _auto_respond_ping(self, index: int):
@@ -179,7 +302,7 @@ class IcingProtocol:
         Called by a Timer to respond automatically to a PING_REQUEST after 2s.
         """
         print(f"{BLUE}[AUTO]{RESET} Delayed responding to PING at index={index}")
-        self.respond_to_ping(index, answer_code=0)
+        self.respond_to_ping(index, answer=1)  # Accept by default
         self.show_state()
 
     def _auto_respond_handshake(self, index: int):
@@ -205,6 +328,140 @@ class IcingProtocol:
         # 4) Show final state
         self.show_state()
 
+    # -------------------------------------------------------------------------
+    # Public Methods for Auto Mode Management
+    # -------------------------------------------------------------------------
+    
+    def start_auto_mode(self):
+        """Start the automatic protocol operation mode."""
+        self.auto_mode.start()
+        
+    def stop_auto_mode(self):
+        """Stop the automatic protocol operation mode."""
+        self.auto_mode.stop()
+        
+    def configure_auto_mode(self, **kwargs):
+        """
+        Configure the automatic mode parameters.
+        
+        Args:
+            **kwargs: Configuration parameters to set. Supported parameters:
+                - ping_response_accept: bool, whether to accept incoming pings
+                - ping_auto_initiate: bool, whether to initiate pings on connection
+                - ping_retry_count: int, number of ping retries
+                - ping_retry_delay: float, seconds between ping retries
+                - ping_timeout: float, seconds to wait for ping response
+                - preferred_cipher: int, preferred cipher (0=AES-GCM, 1=ChaCha20-Poly1305)
+                - handshake_retry_count: int, number of handshake retries
+                - handshake_retry_delay: float, seconds between handshake retries
+                - handshake_timeout: float, seconds to wait for handshake
+                - auto_message_enabled: bool, whether to auto-send messages
+                - message_interval: float, seconds between auto messages
+                - message_content: str, default message content
+                - active_mode: bool, whether to actively initiate protocol
+        """
+        for key, value in kwargs.items():
+            if hasattr(self.auto_mode.config, key):
+                setattr(self.auto_mode.config, key, value)
+                print(f"{BLUE}[CONFIG]{RESET} Set auto mode {key} = {value}")
+            else:
+                print(f"{RED}[ERROR]{RESET} Unknown auto mode configuration parameter: {key}")
+                
+    def get_auto_mode_config(self):
+        """Return the current auto mode configuration."""
+        return self.auto_mode.config
+        
+    def queue_auto_message(self, message: str):
+        """
+        Add a message to the auto-send queue.
+        
+        Args:
+            message: Message text to send
+        """
+        self.auto_mode.queue_message(message)
+        
+    def toggle_auto_mode_logging(self):
+        """
+        Toggle detailed logging for auto mode.
+        When enabled, will show more information about state transitions and decision making.
+        """
+        if not hasattr(self.auto_mode, 'verbose_logging'):
+            self.auto_mode.verbose_logging = True
+        else:
+            self.auto_mode.verbose_logging = not self.auto_mode.verbose_logging
+            
+        status = "enabled" if self.auto_mode.verbose_logging else "disabled"
+        print(f"{BLUE}[AUTO-LOG]{RESET} Detailed logging {status}")
+        
+    def debug_message(self, index: int):
+        """
+        Debug a message in the inbound message queue.
+        Prints detailed information about the message.
+        
+        Args:
+            index: The index of the message in the inbound_messages queue
+        """
+        if index < 0 or index >= len(self.inbound_messages):
+            print(f"{RED}[ERROR]{RESET} Invalid message index {index}")
+            return
+            
+        msg = self.inbound_messages[index]
+        print(f"\n{YELLOW}=== Message Debug [{index}] ==={RESET}")
+        print(f"Type: {msg['type']}")
+        print(f"Length: {len(msg['raw'])} bytes = {len(msg['raw'])*8} bits")
+        print(f"Raw data: {msg['raw'].hex()}")
+        
+        if msg['parsed'] is not None:
+            print(f"\n{YELLOW}--- Parsed Data ---{RESET}")
+            if msg['type'] == 'PING_REQUEST':
+                ping = msg['parsed']
+                print(f"Version: {ping.version}")
+                print(f"Cipher: {ping.cipher} ({'AES-256-GCM' if ping.cipher == 0 else 'ChaCha20-Poly1305' if ping.cipher == 1 else 'Unknown'})")
+                print(f"Session nonce: {ping.session_nonce.hex()}")
+                print(f"CRC32: {ping.crc32:08x}")
+                
+            elif msg['type'] == 'PING_RESPONSE':
+                resp = msg['parsed']
+                print(f"Version: {resp.version}")
+                print(f"Cipher: {resp.cipher} ({'AES-256-GCM' if resp.cipher == 0 else 'ChaCha20-Poly1305' if resp.cipher == 1 else 'Unknown'})")
+                print(f"Answer: {resp.answer} ({'Accept' if resp.answer == 1 else 'Reject'})")
+                print(f"CRC32: {resp.crc32:08x}")
+                
+            elif msg['type'] == 'HANDSHAKE':
+                hs = msg['parsed']
+                print(f"Ephemeral pubkey: {hs.ephemeral_pubkey.hex()[:16]}...")
+                print(f"Ephemeral signature: {hs.ephemeral_signature.hex()[:16]}...")
+                print(f"PFS hash: {hs.pfs_hash.hex()[:16]}...")
+                print(f"Timestamp: {hs.timestamp}")
+                print(f"CRC32: {hs.crc32:08x}")
+                
+            elif msg['type'] == 'ENCRYPTED_MESSAGE':
+                header = msg['parsed']
+                print(f"Flag: 0x{header.flag:04x}")
+                print(f"Data length: {header.data_len} bytes")
+                print(f"Retry: {header.retry}")
+                print(f"Connection status: {header.connection_status} ({'CRC included' if header.connection_status & 0x01 else 'No CRC'})")
+                print(f"IV: {header.iv.hex()}")
+                
+                # Calculate expected message size
+                expected_len = 18 + header.data_len + 16  # Header + payload + tag
+                if header.connection_status & 0x01:
+                    expected_len += 4  # Add CRC
+                    
+                print(f"Expected total length: {expected_len} bytes")
+                print(f"Actual length: {len(msg['raw'])} bytes")
+                
+                # If we have a key, try to decrypt
+                if self.hkdf_key:
+                    print("\nAttempting decryption...")
+                    try:
+                        key = bytes.fromhex(self.hkdf_key)
+                        plaintext = decrypt_message(msg['raw'], key, self.cipher_type)
+                        print(f"Decrypted: {plaintext.decode('utf-8')}")
+                    except Exception as e:
+                        print(f"Decryption failed: {e}")
+        print()
+
     # -------------------------------------------------------------------------
     # Public Methods
     # -------------------------------------------------------------------------
@@ -214,6 +471,9 @@ class IcingProtocol:
         self.connections.append(conn)
         print(f"{GREEN}[IcingProtocol]{RESET} Outgoing connection to port {port} established.")
         
+        # Notify auto mode
+        self.auto_mode.handle_connection_established()
+
     def set_peer_identity(self, peer_pubkey_hex: str):
         pubkey_bytes = bytes.fromhex(peer_pubkey_hex)
         self.peer_identity_pubkey_obj = load_peer_identity_key(pubkey_bytes)
@@ -224,127 +484,167 @@ class IcingProtocol:
         self.ephemeral_privkey, self.ephemeral_pubkey = get_ephemeral_keypair()
         print(f"{GREEN}[IcingProtocol]{RESET} Generated ephemeral key pair: pubkey={self.ephemeral_pubkey.hex()[:16]}...")
 
-    def send_ping_request(self):
+    # Send PING (session discovery and cipher negotiation)
+    def send_ping_request(self, cipher_type=0):
+        """
+        Send a ping request to the first connected peer.
+        
+        Args:
+            cipher_type: Preferred cipher type (0 = AES-256-GCM, 1 = ChaCha20-Poly1305)
+        """
         if not self.connections:
             print(f"{RED}[ERROR]{RESET} No active connections.")
-            return
+            return False
-        pkt = build_ping_request(version=0)
+        
+        # Validate cipher type
+        if cipher_type not in (0, 1):
+            print(f"{YELLOW}[WARNING]{RESET} Invalid cipher type {cipher_type}, defaulting to AES-256-GCM (0)")
+            cipher_type = 0
+            
+        # Create ping request with specified cipher
+        ping_request = PingRequest(version=0, cipher=cipher_type)
+        
+        # Store session nonce if not already set
+        if self.session_nonce is None:
+            self.session_nonce = ping_request.session_nonce
+            print(f"{YELLOW}[NOTICE]{RESET} Stored session nonce from sent PING.")
+            
+        # Serialize and send
+        pkt = ping_request.serialize()
         self._send_packet(self.connections[0], pkt, "PING_REQUEST")
         self.state["ping_sent"] = True
+        return True
 
     def send_handshake(self):
         """
         Build and send handshake:
-          - 32-bit timestamp
           - ephemeral_pubkey (64 bytes, raw x||y)
           - ephemeral_signature (64 bytes, raw r||s)
           - pfs_hash (32 bytes)
-          - 32-bit CRC
+          - timestamp (32 bits)
+          - CRC (32 bits)
         """
         if not self.connections:
             print(f"{RED}[ERROR]{RESET} No active connections.")
-            return
+            return False
         if not self.ephemeral_privkey or not self.ephemeral_pubkey:
             print(f"{RED}[ERROR]{RESET} Ephemeral keys not generated.")
-            return
+            return False
         if self.peer_identity_pubkey_bytes is None:
             print(f"{RED}[ERROR]{RESET} Peer identity not set; needed for PFS tracking.")
-            return
+            return False
 
-        # 1) Sign ephemeral_pubkey as r||s
+        # 1) Sign ephemeral_pubkey using identity key
-        #    Instead of DER, we do raw r||s each 32 bytes
         sig_der = sign_data(self.identity_privkey, self.ephemeral_pubkey)
-        # Convert DER -> (r, s) -> raw 64 bytes
+        # Convert DER signature to raw r||s format (64 bytes)
-        # Quick approach to parse DER using cryptography, or do a custom parse
+        raw_signature = der_to_raw(sig_der)
-        from cryptography.hazmat.primitives.asymmetric.utils import decode_dss_signature
-        r_int, s_int = decode_dss_signature(sig_der)
-        r_bytes = r_int.to_bytes(32, 'big')
-        s_bytes = s_int.to_bytes(32, 'big')
-        raw_signature = r_bytes + s_bytes  # 64 bytes
 
-        # 2) PFS hash
+        # 2) Compute PFS hash
         session_number, last_secret_hex = self.pfs_history.get(self.peer_identity_pubkey_bytes, (-1, ""))
         pfs = compute_pfs_hash(session_number, last_secret_hex)
 
-        # 3) Build handshake
+        # 3) Create handshake object
-        timestamp_32 = int(time.time() * 1000) & 0xffffffff
+        handshake = Handshake(
-        pkt = build_handshake_message(
+            ephemeral_pubkey=self.ephemeral_pubkey,
-            timestamp_32,
+            ephemeral_signature=raw_signature,
-            self.ephemeral_pubkey,  # 64 bytes raw
+            pfs_hash=pfs
-            raw_signature,  # 64 bytes raw
-            pfs  # 32 bytes
         )
 
-        # 4) Send
+        # 4) Serialize and send
+        pkt = handshake.serialize()
         self._send_packet(self.connections[0], pkt, "HANDSHAKE")
         self.state["handshake_sent"] = True
+        return True
 
     def enable_auto_responder(self, enable: bool):
+        """
+        Legacy method for enabling/disabling auto responder.
+        For new code, use start_auto_mode() and stop_auto_mode() instead.
+        """
         self.auto_responder = enable
-        print(f"{BLUE}[AUTO]{RESET} Auto responder set to {enable}.")
+        print(f"{YELLOW}[LEGACY]{RESET} Auto responder set to {enable}. Consider using auto_mode instead.")
 
     # -------------------------------------------------------------------------
     # Manual Responses
     # -------------------------------------------------------------------------
 
-    def respond_to_ping(self, index: int, answer_code: int):
+    def respond_to_ping(self, index: int, answer: int):
         """
-        Manually respond to an inbound PING_REQUEST in inbound_messages[index].
+        Respond to a ping request with the specified answer (0 = no, 1 = yes).
+        If answer is 1, we accept the connection and use the cipher specified in the request.
         """
         if index < 0 or index >= len(self.inbound_messages):
             print(f"{RED}[ERROR]{RESET} Invalid index {index}.")
-            return
+            return False
         msg = self.inbound_messages[index]
         if msg["type"] != "PING_REQUEST":
             print(f"{RED}[ERROR]{RESET} inbound_messages[{index}] is not a PING_REQUEST.")
-            return
+            return False
+
+        ping_request = msg["parsed"]
+        version = ping_request.version
+        cipher = ping_request.cipher
+        
+        # Force cipher to 0 or 1 (only AES-256-GCM and ChaCha20-Poly1305 are supported)
+        if cipher != 0 and cipher != 1:
+            print(f"{YELLOW}[NOTICE]{RESET} Received PING with unsupported cipher ({cipher}); forcing cipher to 0 in response.")
+            cipher = 0
+            
+        # Store the negotiated cipher type if we're accepting
+        if answer == 1:
+            self.cipher_type = cipher
 
-        version = msg["parsed"]["version"]
         conn = msg["connection"]
-        resp = build_ping_response(version, answer_code)
+        # Create ping response
+        ping_response = PingResponse(version, cipher, answer)
+        resp = ping_response.serialize()
         self._send_packet(conn, resp, "PING_RESPONSE")
-        print(f"{BLUE}[MANUAL]{RESET} Responded to ping with answer_code={answer_code}.")
+        print(f"{BLUE}[MANUAL]{RESET} Responded to ping with answer={answer}.")
+        return True
 
     def generate_ecdhe(self, index: int):
         """
-        Formerly 'respond_to_handshake'. Verifies the inbound ephemeral signature
+        Process a handshake message:
-        and computes the ECDH shared secret, updating PFS history.
+        1. Verify the ephemeral signature
+        2. Compute the ECDH shared secret
+        3. Update PFS history
         """
         if index < 0 or index >= len(self.inbound_messages):
             print(f"{RED}[ERROR]{RESET} Invalid index {index}.")
-            return
+            return False
         msg = self.inbound_messages[index]
         if msg["type"] != "HANDSHAKE":
             print(f"{RED}[ERROR]{RESET} inbound_messages[{index}] is not a HANDSHAKE.")
-            return
+            return False
 
-        ephemeral_pub = msg["parsed"]["ephemeral_pub"]
+        handshake = msg["parsed"]
-        ephemeral_sig = msg["parsed"]["ephemeral_sig"]
         
-        # Use our raw_signature_to_der wrapper only if signature is 64 bytes.
+        # Convert raw signature to DER for verification
-        # Otherwise, assume the signature is already DER-encoded.
+        raw_sig = handshake.ephemeral_signature
-        from crypto_utils import raw_signature_to_der
+        sig_der = raw_signature_to_der(raw_sig)
-        if len(ephemeral_sig) == 64:
-            sig_der = raw_signature_to_der(ephemeral_sig)
-        else:
-            sig_der = ephemeral_sig
 
-        ok = verify_signature(self.peer_identity_pubkey_obj, sig_der, ephemeral_pub)
+        # Verify signature
+        ok = verify_signature(self.peer_identity_pubkey_obj, sig_der, handshake.ephemeral_pubkey)
         if not ok:
             print(f"{RED}[ERROR]{RESET} Ephemeral signature invalid.")
-            return
+            return False
         print(f"{GREEN}[OK]{RESET} Ephemeral signature verified.")
 
+        # Check if we have ephemeral keys
         if not self.ephemeral_privkey:
             print(f"{YELLOW}[WARN]{RESET} No ephemeral_privkey available, cannot compute shared secret.")
-            return
+            return False
-        shared = compute_ecdh_shared_key(self.ephemeral_privkey, ephemeral_pub)
+            
+        # Compute ECDH shared secret
+        shared = compute_ecdh_shared_key(self.ephemeral_privkey, handshake.ephemeral_pubkey)
         self.shared_secret = shared.hex()
         print(f"{GREEN}[OK]{RESET} Computed ECDH shared key = {self.shared_secret}")
 
+        # Update PFS history
         old_session, _ = self.pfs_history.get(self.peer_identity_pubkey_bytes, (-1, ""))
         new_session = 1 if old_session < 0 else old_session + 1
         self.pfs_history[self.peer_identity_pubkey_bytes] = (new_session, self.shared_secret)
+        return True
 
     # -------------------------------------------------------------------------
     # Utility
@@ -373,11 +673,30 @@ class IcingProtocol:
 
         print(f"\nShared Secret: {self.shared_secret if self.shared_secret else '[None]'}")
 
+        if self.hkdf_key:
+            print(f"HKDF Derived Key: {self.hkdf_key} (size: {len(self.hkdf_key)*8} bits)")
+        else:
+            print("HKDF Derived Key: [None]")
+            
+        print(f"Negotiated Cipher: {'AES-256-GCM' if self.cipher_type == 0 else 'ChaCha20-Poly1305'} (code: {self.cipher_type})")
+        
+        if self.session_nonce:
+            print(f"Session Nonce: {self.session_nonce.hex()} (129 bits)")
+        else:
+            print("Session Nonce: [None]")
+            
+        if self.last_iv:
+            print(f"Last IV: {self.last_iv.hex()} (96 bits)")
+        else:
+            print("Last IV: [None]")
+            
         print("\nProtocol Flags:")
         for k, v in self.state.items():
             print(f"  {k}: {v}")
 
-        print("\nAuto Responder:", self.auto_responder)
+        print("\nAuto Mode Active:", self.auto_mode.active)
+        print("Auto Mode State:", self.auto_mode.state)
+        print("Legacy Auto Responder:", self.auto_responder)
 
         print("\nActive Connections:")
         for i, c in enumerate(self.connections):
@@ -389,9 +708,108 @@ class IcingProtocol:
         print()
 
     def stop(self):
+        """Stop the protocol and clean up resources."""
+        # Stop auto mode first
+        self.auto_mode.stop()
+        
+        # Stop server listener
         self.server_listener.stop()
+        
+        # Close all connections
         for c in self.connections:
             c.close()
         self.connections.clear()
         self.inbound_messages.clear()
         print(f"{RED}[STOP]{RESET} Protocol stopped.")
+
+    # -------------------------------------------------------------------------
+    # Encrypted Messaging
+    # -------------------------------------------------------------------------
+
+    def send_encrypted_message(self, plaintext: str):
+        """
+        Encrypts and sends a message using the derived HKDF key and negotiated cipher.
+        The message format is:
+        - Header (18 bytes): flag, data_len, retry, connection_status, IV
+        - Payload: variable length encrypted data
+        - Footer: Authentication tag (16 bytes) + optional CRC32 (4 bytes)
+        """
+        if not self.connections:
+            print(f"{RED}[ERROR]{RESET} No active connections.")
+            return False
+        if not self.hkdf_key:
+            print(f"{RED}[ERROR]{RESET} No HKDF key derived. Cannot encrypt message.")
+            return False
+            
+        # Get the encryption key
+        key = bytes.fromhex(self.hkdf_key)
+        
+        # Convert plaintext to bytes
+        plaintext_bytes = plaintext.encode('utf-8')
+        
+        # Generate or increment the IV
+        if self.last_iv is None:
+            # First message, generate random IV
+            iv = generate_iv(initial=True)
+        else:
+            # Subsequent message, increment previous IV
+            iv = generate_iv(initial=False, previous_iv=self.last_iv)
+            
+        # Store the new IV
+        self.last_iv = iv
+        
+        # Create encrypted message (connection_status 0 = no CRC)
+        encrypted = encrypt_message(
+            plaintext=plaintext_bytes,
+            key=key,
+            flag=0xBEEF,  # Default flag
+            retry=0,
+            connection_status=0,  # No CRC
+            iv=iv,
+            cipher_type=self.cipher_type
+        )
+        
+        # Send the encrypted message
+        self._send_packet(self.connections[0], encrypted, "ENCRYPTED_MESSAGE")
+        print(f"{GREEN}[SEND_ENCRYPTED]{RESET} Encrypted message sent.")
+        return True
+
+    def decrypt_received_message(self, index: int):
+        """
+        Decrypt a received encrypted message using the HKDF key and negotiated cipher.
+        """
+        if index < 0 or index >= len(self.inbound_messages):
+            print(f"{RED}[ERROR]{RESET} Invalid message index.")
+            return None
+            
+        msg = self.inbound_messages[index]
+        if msg["type"] != "ENCRYPTED_MESSAGE":
+            print(f"{RED}[ERROR]{RESET} Message at index {index} is not an ENCRYPTED_MESSAGE.")
+            return None
+            
+        # Get the encrypted message
+        encrypted = msg["raw"]
+        
+        if not self.hkdf_key:
+            print(f"{RED}[ERROR]{RESET} No HKDF key derived. Cannot decrypt message.")
+            return None
+            
+        # Get the encryption key
+        key = bytes.fromhex(self.hkdf_key)
+        
+        try:
+            # Decrypt the message
+            plaintext = decrypt_message(encrypted, key, self.cipher_type)
+            
+            # Convert to string
+            plaintext_str = plaintext.decode('utf-8')
+            
+            # Update last IV from the header
+            header = MessageHeader.unpack(encrypted[:18])
+            self.last_iv = header.iv
+            
+            print(f"{GREEN}[DECRYPTED]{RESET} Decrypted message: {plaintext_str}")
+            return plaintext_str
+        except Exception as e:
+            print(f"{RED}[ERROR]{RESET} Decryption failed: {e}")
+            return None