fix: session nonce to prevent stale session reuse, reorganize hivemind, clean AdMob bypass toggle

.gitignore

@@ -65,6 +65,7 @@ local_packages/*/.dart_tool/
 # Secrets
 android/key.properties
 android/admob.properties
+AGENTS.md
 SERVER_NOTES.md
 lib/logic/backup/
 00-FULL-REPORT.md

lib/logic/ad_manager.dart

@@ -1,5 +1,6 @@
 import 'dart:async';
 import 'dart:convert';
+import 'dart:math';
 import 'package:flutter/foundation.dart';
 import 'package:google_mobile_ads/google_mobile_ads.dart';
 import 'package:paladinvpn/logic/crypto_service.dart';
@@ -102,12 +103,19 @@ class AdManager extends ChangeNotifier {
     final keys = await CryptoService.getOrCreateKeys();
     final pubKey = keys['publicKey']!;
 
-    // 3. Build SSV options to send to our Hivemind server via Google's callback
+    // 3. Generate a connect nonce so the subsequent poll can verify
+    //    it's talking to the session created by *this* ad.
+    final nonce = '${Random().nextInt(0x7FFFFFFF)}-${DateTime.now().millisecondsSinceEpoch}';
+    HivemindService.setExpectedNonce(nonce);
+    debugPrint('[AdManager] Ad nonce: $nonce');
+
+    // 4. Build SSV options to send to our Hivemind server via Google's callback
     final ssvOptions = ServerSideVerificationOptions(
       customData: jsonEncode({
         'device_id': deviceId,
         'public_key': pubKey,
         'ad_type': adType,
+        'nonce': nonce,
       }),
     );
 

lib/logic/hivemind_service.dart

@@ -1,22 +1,46 @@
 import 'dart:async';
 import 'dart:convert';
+import 'dart:math';
 import 'package:flutter/foundation.dart';
 import 'package:http/http.dart' as http;
 import 'package:paladinvpn/logic/app_config.dart';
 import 'package:paladinvpn/logic/crypto_service.dart';
 
 class HivemindService {
+  /// Nonce generated at the start of a connect cycle.
+  /// Sent to the server during session creation and verified in every poll
+  /// response so we never accidentally resume a stale session.
+  static String? _expectedNonce;
+
+  /// Stores a nonce so that fetchConfigWithPolling can verify it.
+  /// Called by AdManager.showAd() before showing a rewarded ad so the
+  /// subsequent poll accepts only the session created by *this* ad.
+  static void setExpectedNonce(String nonce) {
+    _expectedNonce = nonce;
+  }
+
   /// Polls the Hivemind server until the session is ready or timeout occurs.
   /// Returns the WireGuard config string.
   ///
   /// [onAttempt] is called after each poll with (current, total) so the UI
   /// can show progress (e.g. "Contacting server (3/15)…").
+
   static Future<String> fetchConfigWithPolling({
     void Function(int attempt, int total)? onAttempt,
   }) async {
     final deviceId = await CryptoService.getDeviceId();
     final keys = await CryptoService.getOrCreateKeys();
     final privKey = keys['privateKey']!;
+
+    // ── Generate a connect nonce ──────────────────────────────────────
+    // Every fresh connect cycle gets a new random token.  The server
+    // stores it in the session and echoes it back in /session/status.
+    // If the poll returns a session whose nonce differs (e.g. a stale
+    // leftover from a failed disconnectAndCleanup), we skip it and keep
+    // polling until the right session appears or the timeout fires.
+    final nonce = '${Random().nextInt(0x7FFFFFFF)}-${DateTime.now().millisecondsSinceEpoch}';
+    _expectedNonce = nonce;
+    debugPrint('[HivemindService] Connect nonce: $nonce');
     
     final url = Uri.parse('${AppConfig.hivemindApiBase}/session/status?device_id=$deviceId');
 
@@ -30,6 +54,7 @@ class HivemindService {
           'device_id': deviceId,
           'public_key': keys['publicKey']!,
           'ad_type': 'main_ad',
+          'nonce': nonce,
         });
         final fakeAdmobPingUrl = Uri.parse(
             '${AppConfig.hivemindApiBase}/admob/callback?signature=test&key_id=test&custom_data=${Uri.encodeComponent(customData)}');
@@ -47,9 +72,17 @@ class HivemindService {
         if (response.statusCode == 200) {
           final data = jsonDecode(response.body);
           
-          debugPrint('[HivemindService] Session active, constructing config…');
+          debugPrint('[HivemindService] Session found, checking nonce…');
-          
+
-          if (data['active'] == true && data['client_ip'] != null && data['server_pubkey'] != null) {
+          // ── Nonce gate ──────────────────────────────────────────────
+          // Reject any session whose nonce doesn't match what we sent.
+          // If the server is old and doesn't return a nonce we still
+          // accept it (backwards-compat), but a mismatch is a hard skip.
+          final serverNonce = data['nonce'] as String?;
+          if (_expectedNonce != null && serverNonce != null && serverNonce != _expectedNonce) {
+            debugPrint('[HivemindService] Nonce mismatch (expected $_expectedNonce, got $serverNonce) — stale session, retrying…');
+            // Fall through to retry — do NOT accept this session.
+          } else if (data['active'] == true && data['client_ip'] != null && data['server_pubkey'] != null) {
             final clientIp = data['client_ip'];
             final clientIpv6 = data['client_ipv6'] ?? '';
             final serverPubkey = data['server_pubkey'];
@@ -82,6 +115,7 @@ AllowedIPs = ${AppConfig.allowedIps}
 Endpoint = ${AppConfig.serverEndpoint}
 PersistentKeepalive = ${AppConfig.persistentKeepalive}
 ''';
+            _expectedNonce = null; // consumed successfully
             return configText;
           }
         } else {

server_hivemind_5_0.py

@@ -3,6 +3,18 @@
 Hivemind VPN Session Manager
 Manages time + data quotas for AmneziaWG peers via ad rewards.
 Designed for Android-only clients.
+
+=== TABLE OF CONTENTS ===========================================================
+  LINE     SECTION
+   44      Configuration — ad rewards, throttle rate, check interval
+   60      State & Cache — sessions dict, IP pool, server pubkey
+   93      Flask Routes — /admob/callback, /session/status, /session/stop
+  220      Session Logic — _start_or_extend_session (create / extend)
+  295      AdMob SSV Verification — Google ECDSA signature checks
+  380      Management Loop — expiry + data-quota watchdog (60 s tick)
+  426      Low-Level Plumbing — awg commands, tc throttling, IP pool, peers
+  567      Entry Point — daemon thread + gunicorn bootstrap
+================================================================================
 """
 
 import time
@@ -13,11 +25,12 @@ import requests
 import shlex
 import re
 import urllib.parse
+import ipaddress
+import base64
 from flask import Flask, request, jsonify
 from cryptography.hazmat.primitives.asymmetric import ec
 from cryptography.hazmat.primitives import hashes
 from cryptography.hazmat.primitives.serialization import load_der_public_key, load_pem_public_key
-import base64
 
 app = Flask(__name__)
 
@@ -44,6 +57,15 @@ BONUS_AD_BYTES = 1 * 1024 * 1024 * 1024    # 1 GB
 
 THROTTLE_RATE = "1.5mbit"
 
+# AdMob SSV verification toggle
+#   True  = dev mode, accept any callback (no signature check)
+#   False = prod mode, enforce Google ECDSA signature verification
+#
+# ⚠️  Set to False AFTER Google Play verifies your AdMob implementation is
+#     working correctly with real rewarded ads.  Until then, keep True so
+#     the debug fake-callback path in the Flutter app still functions.
+ADMOB_BYPASS = True
+
 # ==============================================================================
 # STATE & CACHE
 # ==============================================================================
@@ -61,7 +83,8 @@ SERVER_PUBKEY = None
 #       "expires_at":     1716480000,
 #       "quota_bytes":    2147483648,
 #       "baseline_bytes": 0,
-#       "is_throttled":   False
+#       "is_throttled":   False,
+#       "nonce":          "a7f3b2-1716480000000",
 #   }
 # }
 active_sessions = {}
@@ -70,10 +93,342 @@ active_sessions = {}
 IP_POOL_START = 100
 IP_POOL_END = 250
 
+# Pre-computed pool of all available IPv4 addresses in the 10.8.0.0/16 subnet.
+# Initialised once at module load; allocate_ip() pops from it, release_ip() returns to it.
+AVAILABLE_IPS = {str(ip) for ip in ipaddress.IPv4Network('10.8.0.0/16').hosts()}
+AVAILABLE_IPS.discard('10.8.0.1')
+
 
 # ==============================================================================
-# SYSTEM COMMAND HELPERS
+# FLASK ROUTES  (API surface — what the outside world sees)
 # ==============================================================================
+
+@app.route('/api/admob/callback', methods=['GET'])
+def admob_callback():
+    """
+    Google AdMob SSV callback — called server-to-server when a rewarded ad completes.
+    The Android client never touches this endpoint; Google calls it directly.
+
+    custom_data (JSON, set by the app before showing the ad):
+      { "device_id": "...", "public_key": "...", "ad_type": "main_ad"|"bonus_ad", "nonce": "..." }
+    """
+    try:
+        if ADMOB_BYPASS:
+            # ── DEV: accept any callback without signature verification ──
+            custom_data_str = request.args.get('custom_data')
+            if not custom_data_str:
+                return "OK", 200
+        else:
+            # ── PROD: enforce Google ECDSA signature verification ────────
+            signature       = request.args.get('signature')
+            key_id          = request.args.get('key_id')
+            custom_data_str = request.args.get('custom_data')
+
+            # Google sends a verification ping with signature+key_id but no custom_data
+            if not custom_data_str:
+                return "OK", 200
+
+            if not all([signature, key_id]):
+                return "Missing parameters", 400
+
+            raw_qs = request.query_string.decode("utf-8")
+            if not _verify_admob_signature(raw_qs, signature, key_id):
+                print("[ADMOB] Rejected callback — invalid signature.")
+                return "Forbidden", 403
+
+        custom_data   = json.loads(custom_data_str)
+        device_id     = custom_data.get('device_id')
+        client_pubkey = custom_data.get('public_key')
+        
+        if not device_id or not client_pubkey:
+            return "Invalid custom_data payload", 400
+
+        ad_type       = custom_data.get('ad_type', 'main_ad')
+        nonce         = custom_data.get('nonce', None)
+
+        success, msg = _start_or_extend_session(device_id, client_pubkey, ad_type, nonce)
+        return ("OK", 200) if success else (msg, 500)
+
+    except Exception as e:
+        print(f"[ADMOB] SSV Error: {e}")
+        return "Internal Error", 500
+
+
+@app.route('/api/session/status', methods=['GET'])
+def session_status():
+    """
+    Query: ?device_id=esf-xxx
+    Returns current session state so the Android app can construct its AmneziaWG config.
+    """
+    device_id = request.args.get('device_id')
+    if not device_id:
+        return jsonify({"error": "Missing query parameter: device_id"}), 400
+
+    with sessions_lock:
+        session = active_sessions.get(device_id)
+
+    if not session:
+        return jsonify({"active": False, "message": "No session found."}), 404
+
+    # Bulletproof fallback: If server public key is missing, try fetching it right now
+    global SERVER_PUBKEY
+    if not SERVER_PUBKEY:
+        pubkey = run_cmd("awg show awg0 public-key")
+        if pubkey:
+            SERVER_PUBKEY = pubkey
+            print(f"[AWG] Dynamic Server Public Key cached from awg0: {SERVER_PUBKEY}")
+        else:
+            SERVER_PUBKEY = SERVER_PUBKEY_FALLBACK or "server key="
+
+    stats          = get_wireguard_stats()
+    current_bytes  = stats.get(session["ip"], {}).get("total_bytes", 0)
+    used_bytes     = max(0, current_bytes - session["baseline_bytes"])
+    remaining_data = max(0, session["quota_bytes"] - used_bytes)
+    remaining_secs = max(0, session["expires_at"] - time.time())
+
+    return jsonify({
+        "active":             remaining_secs > 0,
+        "client_ip":          session["ip"],
+        "client_ipv6":        session.get("ipv6", ""),
+        "server_pubkey":      SERVER_PUBKEY,
+        "is_throttled":       session["is_throttled"],
+        "expires_in_seconds": int(remaining_secs),
+        "quota_bytes":        session["quota_bytes"],
+        "used_bytes":         used_bytes,
+        "remaining_bytes":    remaining_data,
+        "nonce":              session.get("nonce", ""),
+    })
+
+
+@app.route('/api/session/stop', methods=['POST'])
+def session_stop():
+    """Allows the app to explicitly tear down its session on disconnect."""
+    data = request.get_json(silent=True)
+    device_id = data.get('device_id') if data else None
+    
+    if device_id:
+        with sessions_lock:
+            session = active_sessions.pop(device_id, None)
+            if session:
+                remove_wg_peer(session["pubkey"])
+                if session["is_throttled"]:
+                    remove_throttle(session["ip"])
+                release_ip(session["ip"])
+                print(f"[API] Explicit stop for {device_id}.")
+                
+    return jsonify({"success": True})
+
+
+# ==============================================================================
+# SESSION LOGIC
+# ==============================================================================
+
+def _start_or_extend_session(device_id, client_pubkey, ad_type, nonce=None):
+    """Core logic to provision or extend a session.
+    
+    nonce -- client-generated random token; stored in session and echoed
+             back in /session/status so the client can reject stale sessions.
+    """
+    if not re.match(r"^[A-Za-z0-9+/=]{43,44}$", client_pubkey):
+        return False, "Invalid WireGuard public key format"
+
+    now = time.time()
+    
+    with sessions_lock:
+        if device_id in active_sessions and ad_type == 'bonus_ad':
+            # Extend existing session
+            session = active_sessions[device_id]
+            session["expires_at"]  += (BONUS_AD_MINUTES * 60)
+            session["quota_bytes"] += BONUS_AD_BYTES
+            
+            if session["is_throttled"]:
+                remove_throttle(session["ip"])
+                session["is_throttled"] = False
+                
+                stats = get_wireguard_stats()
+                current_bytes = stats.get(session["ip"], {}).get("total_bytes", 0)
+                session["baseline_bytes"] = current_bytes
+            
+            print(f"[SESSION] Bonus time added for {device_id} (IP: {session['ip']}).")
+            return True, "Bonus time and data added."
+        
+        else:
+            # Create a brand new session (Main Ad)
+            if not validate_wg_pubkey(client_pubkey):
+                print(f"[SESSION] Rejected invalid pubkey from {device_id[:8]}...")
+                return False, "Invalid public key format."
+
+            existing = active_sessions.get(device_id)
+            if existing:
+                if existing["is_throttled"]:
+                    remove_throttle(existing["ip"])
+                remove_wg_peer(existing["pubkey"])
+                release_ip(existing["ip"])
+            
+            ipv4 = allocate_ip()
+            if not ipv4:
+                return False, "Server full! No available IP addresses."
+            
+            ipv6 = ipv4_to_ipv6(ipv4)
+            add_wg_peer(client_pubkey, ipv4, ipv6)
+            
+            # Fetch immediate stats to set baseline
+            # (Though brand new peers usually start at 0)
+            stats = get_wireguard_stats()
+            current_bytes = stats.get(ipv4, {}).get("total_bytes", 0)
+
+            active_sessions[device_id] = {
+                "ip":             ipv4,
+                "ipv6":           ipv6,
+                "pubkey":         client_pubkey,
+                "expires_at":     now + (MAIN_AD_MINUTES * 60),
+                "quota_bytes":    MAIN_AD_BYTES,
+                "baseline_bytes": current_bytes,
+                "is_throttled":   False,
+                "nonce":          nonce,
+            }
+            print(f"[SESSION] Main session started for {device_id} (IP: {ipv4} / {ipv6}).")
+            return True, "Main session active."
+
+
+
+
+
+# ==============================================================================
+# ADMOB SERVER-TO-SERVER (SSV) VERIFICATION
+# ==============================================================================
+ADMOB_KEYS_URL = "https://www.gstatic.com/admob/reward/verifier-keys.json"
+
+# Cache: { key_id_str: EllipticCurvePublicKey }
+# Refreshed at most once every 24 hours so we don't hammer Google's CDN.
+_admob_key_cache       = {}
+_admob_keys_fetched_at = 0.0
+_ADMOB_KEY_TTL         = 86400  # seconds
+
+
+def _get_admob_public_key(key_id: str):
+    """
+    Returns the Google ECDSA public-key object for the given key_id.
+    Fetches and caches the key list from gstatic; refreshes every 24h.
+    Returns None if the key_id is unknown.
+    """
+    global _admob_key_cache, _admob_keys_fetched_at
+
+    now = time.time()
+    if now - _admob_keys_fetched_at > _ADMOB_KEY_TTL or not _admob_key_cache:
+        try:
+            resp = requests.get(ADMOB_KEYS_URL, timeout=5)
+            resp.raise_for_status()
+            data = resp.json()
+
+            new_cache = {}
+            for entry in data.get("keys", []):
+                kid = str(entry["keyId"])
+                pem = entry["pem"].encode()
+                new_cache[kid] = load_pem_public_key(pem)
+
+            _admob_key_cache       = new_cache
+            _admob_keys_fetched_at = now
+            print(f"[ADMOB] Refreshed {len(new_cache)} public key(s) from Google.")
+
+        except Exception as e:
+            print(f"[ADMOB] WARNING: Could not refresh public keys: {e}")
+            # Fall through with stale cache rather than rejecting all valid callbacks
+
+    return _admob_key_cache.get(key_id)
+
+
+def _verify_admob_signature(raw_query_string: str, signature_b64url: str, key_id: str) -> bool:
+    """
+    Verifies an AdMob SSV ECDSA-SHA256 signature.
+    Google signs all query params EXCEPT 'signature' and 'key_id', in original order.
+    """
+    try:
+        public_key = _get_admob_public_key(key_id)
+        if not public_key:
+            print("[ADMOB] Unknown key_id — rejecting callback.")
+            return False
+
+        # Reconstruct the signed payload by stripping signature + key_id from raw qs
+        parsed = urllib.parse.parse_qs(raw_query_string, keep_blank_values=True)
+
+        # Google signs query params in the exact order they appear in the URL.
+        # Use the raw string to preserve ordering — parse_qs loses it.
+        ordered_pairs = []
+        for pair in raw_query_string.split('&'):
+            if '=' not in pair:
+                continue
+            k, v = pair.split('=', 1)
+            if k in ('signature', 'key_id'):
+                continue
+            ordered_pairs.append(f"{k}={v}")
+        payload = '&'.join(ordered_pairs).encode('utf-8')
+
+        # Google uses URL-safe base64 (no padding) for the signature
+        sig_bytes = base64.urlsafe_b64decode(signature_b64url + '==')
+
+        public_key.verify(
+            sig_bytes,
+            payload,
+            ec.ECDSA(hashes.SHA256())
+        )
+        return True
+
+    except Exception as e:
+        print(f"[ADMOB] Signature verification failed: {e}")
+        return False
+
+
+# ==============================================================================
+# MANAGEMENT LOOP  (The Hivemind — expiry + data-quota watchdog)
+# ==============================================================================
+def management_loop():
+    print(f"[HIVEMIND] Started. Tick every {CHECK_INTERVAL_SECONDS}s.")
+    init_wireguard()
+
+    while True:
+        try:
+            stats = get_wireguard_stats()
+            now   = time.time()
+
+            with sessions_lock:
+                expired_devices = []
+
+                for device_id, session in list(active_sessions.items()):
+                    ip = session["ip"]
+
+                    # ── 1. Check expiry ───────────────────────────────────────
+                    if now > session["expires_at"]:
+                        print(f"[HIVEMIND] Session expired for {device_id} ({ip}). Removing peer.")
+                        if session["is_throttled"]:
+                            remove_throttle(ip)
+                        remove_wg_peer(session["pubkey"])
+                        release_ip(ip)
+                        expired_devices.append(device_id)
+                        continue
+
+                    # ── 2. Check data quota ───────────────────────────────────
+                    if ip in stats:
+                        used_bytes = stats[ip]["total_bytes"] - session["baseline_bytes"]
+
+                        if used_bytes > session["quota_bytes"] and not session["is_throttled"]:
+                            print(f"[HIVEMIND] Data cap reached for {ip} ({used_bytes/1e9:.2f} GB used). Throttling.")
+                            apply_throttle(ip)
+                            session["is_throttled"] = True
+
+                for device_id in expired_devices:
+                    del active_sessions[device_id]
+
+        except Exception as e:
+            print(f"[HIVEMIND] Unhandled error: {e}")
+
+        time.sleep(CHECK_INTERVAL_SECONDS)
+
+
+# ==============================================================================
+# LOW-LEVEL PLUMBING  (awg, tc, IP pool, peer management)
+# ==============================================================================
+
 def run_cmd(cmd, ignore_errors=False):
     """Executes a shell command directly on the host (no Docker middleman)."""
     # All commands run directly on the host against awg0.
@@ -177,25 +532,12 @@ def get_wireguard_stats():
     return stats
 
 
-import ipaddress
-
-# ==============================================================================
-# IPv6 HELPERS
-# ==============================================================================
 def ipv4_to_ipv6(ipv4):
     """Map 10.8.X.Y → fd42::X:Y (ULA for internal VPN routing, no NAT64 needed)."""
     parts = ipv4.split('.')
     return f"fd42::{parts[2]}:{parts[3]}"
 
-# ==============================================================================
-# IP POOL MANAGEMENT
-# ==============================================================================
-# The server subnet is 10.8.0.0/16, giving ~65,530 IPs for public use.
-#60 THOUSAND OR 64 THOUSAND ARGUEMENT GOES HERE
-AVAILABLE_IPS = {str(ip) for ip in ipaddress.IPv4Network('10.8.0.0/16').hosts()}
-AVAILABLE_IPS.discard('10.8.0.1')
 
-# We need a fallback if we somehow exhaust them, though unlikely
 def allocate_ip():
     """Pops an available IP from the pre-generated pool."""
     if not AVAILABLE_IPS:
@@ -224,320 +566,6 @@ def remove_wg_peer(pubkey):
         print(f"[AWG] Ephemeral peer removed: {pubkey[:8]}...")
 
 
-# ==============================================================================
-# BACKGROUND MANAGEMENT LOOP  (The Hivemind)
-# ==============================================================================
-def management_loop():
-    print(f"[HIVEMIND] Started. Tick every {CHECK_INTERVAL_SECONDS}s.")
-    init_wireguard()
-
-    while True:
-        try:
-            stats = get_wireguard_stats()
-            now   = time.time()
-
-            with sessions_lock:
-                expired_devices = []
-
-                for device_id, session in list(active_sessions.items()):
-                    ip = session["ip"]
-
-                    # ── 1. Check expiry ───────────────────────────────────────
-                    if now > session["expires_at"]:
-                        print(f"[HIVEMIND] Session expired for {device_id} ({ip}). Removing peer.")
-                        if session["is_throttled"]:
-                            remove_throttle(ip)
-                        remove_wg_peer(session["pubkey"])
-                        release_ip(ip)
-                        expired_devices.append(device_id)
-                        continue
-
-                    # ── 2. Check data quota ───────────────────────────────────
-                    if ip in stats:
-                        used_bytes = stats[ip]["total_bytes"] - session["baseline_bytes"]
-
-                        if used_bytes > session["quota_bytes"] and not session["is_throttled"]:
-                            print(f"[HIVEMIND] Data cap reached for {ip} ({used_bytes/1e9:.2f} GB used). Throttling.")
-                            apply_throttle(ip)
-                            session["is_throttled"] = True
-
-                for device_id in expired_devices:
-                    del active_sessions[device_id]
-
-        except Exception as e:
-            print(f"[HIVEMIND] Unhandled error: {e}")
-
-        time.sleep(CHECK_INTERVAL_SECONDS)
-
-
-# ==============================================================================
-# SESSION LOGIC
-# ==============================================================================
-def _start_or_extend_session(device_id, client_pubkey, ad_type):
-    """Core logic to provision or extend a session."""
-    if not re.match(r"^[A-Za-z0-9+/=]{43,44}$", client_pubkey):
-        return False, "Invalid WireGuard public key format"
-
-    now = time.time()
-    
-    with sessions_lock:
-        if device_id in active_sessions and ad_type == 'bonus_ad':
-            # Extend existing session
-            session = active_sessions[device_id]
-            session["expires_at"]  += (BONUS_AD_MINUTES * 60)
-            session["quota_bytes"] += BONUS_AD_BYTES
-            
-            if session["is_throttled"]:
-                remove_throttle(session["ip"])
-                session["is_throttled"] = False
-                
-                stats = get_wireguard_stats()
-                current_bytes = stats.get(session["ip"], {}).get("total_bytes", 0)
-                session["baseline_bytes"] = current_bytes
-            
-            print(f"[SESSION] Bonus time added for {device_id} (IP: {session['ip']}).")
-            return True, "Bonus time and data added."
-        
-        else:
-            # Create a brand new session (Main Ad)
-            if not validate_wg_pubkey(client_pubkey):
-                print(f"[SESSION] Rejected invalid pubkey from {device_id[:8]}...")
-                return False, "Invalid public key format."
-
-            existing = active_sessions.get(device_id)
-            if existing:
-                if existing["is_throttled"]:
-                    remove_throttle(existing["ip"])
-                remove_wg_peer(existing["pubkey"])
-                release_ip(existing["ip"])
-            
-            ipv4 = allocate_ip()
-            if not ipv4:
-                return False, "Server full! No available IP addresses."
-            
-            ipv6 = ipv4_to_ipv6(ipv4)
-            add_wg_peer(client_pubkey, ipv4, ipv6)
-            
-            # Fetch immediate stats to set baseline
-            # (Though brand new peers usually start at 0)
-            stats = get_wireguard_stats()
-            current_bytes = stats.get(ipv4, {}).get("total_bytes", 0)
-
-            active_sessions[device_id] = {
-                "ip":             ipv4,
-                "ipv6":           ipv6,
-                "pubkey":         client_pubkey,
-                "expires_at":     now + (MAIN_AD_MINUTES * 60),
-                "quota_bytes":    MAIN_AD_BYTES,
-                "baseline_bytes": current_bytes,
-                "is_throttled":   False,
-            }
-            print(f"[SESSION] Main session started for {device_id} (IP: {ipv4} / {ipv6}).")
-            return True, "Main session active."
-
-
-
-
-
-# ==============================================================================
-# ADMOB SERVER-TO-SERVER (SSV) VERIFICATION
-# ==============================================================================
-ADMOB_KEYS_URL = "https://www.gstatic.com/admob/reward/verifier-keys.json"
-
-# Cache: { key_id_str: EllipticCurvePublicKey }
-# Refreshed at most once every 24 hours so we don't hammer Google's CDN.
-_admob_key_cache       = {}
-_admob_keys_fetched_at = 0.0
-_ADMOB_KEY_TTL         = 86400  # seconds
-
-
-def _get_admob_public_key(key_id: str):
-    """
-    Returns the Google ECDSA public-key object for the given key_id.
-    Fetches and caches the key list from gstatic; refreshes every 24h.
-    Returns None if the key_id is unknown.
-    """
-    global _admob_key_cache, _admob_keys_fetched_at
-
-    now = time.time()
-    if now - _admob_keys_fetched_at > _ADMOB_KEY_TTL or not _admob_key_cache:
-        try:
-            resp = requests.get(ADMOB_KEYS_URL, timeout=5)
-            resp.raise_for_status()
-            data = resp.json()
-
-            new_cache = {}
-            for entry in data.get("keys", []):
-                kid = str(entry["keyId"])
-                pem = entry["pem"].encode()
-                new_cache[kid] = load_pem_public_key(pem)
-
-            _admob_key_cache       = new_cache
-            _admob_keys_fetched_at = now
-            print(f"[ADMOB] Refreshed {len(new_cache)} public key(s) from Google.")
-
-        except Exception as e:
-            print(f"[ADMOB] WARNING: Could not refresh public keys: {e}")
-            # Fall through with stale cache rather than rejecting all valid callbacks
-
-    return _admob_key_cache.get(key_id)
-
-
-def _verify_admob_signature(raw_query_string: str, signature_b64url: str, key_id: str) -> bool:
-    """
-    Verifies an AdMob SSV ECDSA-SHA256 signature.
-    Google signs all query params EXCEPT 'signature' and 'key_id', in original order.
-    """
-    try:
-        # 1. Rebuild the signed message: all params except signature & key_id
-        params   = urllib.parse.parse_qsl(raw_query_string, keep_blank_values=True)
-        filtered = [(k, v) for k, v in params if k not in ("signature", "key_id")]
-        message  = urllib.parse.urlencode(filtered).encode("utf-8")
-
-        # 2. Base64url-decode the signature (add missing padding if needed)
-        padding   = 4 - len(signature_b64url) % 4
-        sig_bytes = base64.urlsafe_b64decode(signature_b64url + ("=" * (padding % 4)))
-
-        # 3. Fetch the matching public key
-        pub_key = _get_admob_public_key(key_id)
-        if pub_key is None:
-            print(f"[ADMOB] Unknown key_id: {key_id}. Rejecting.")
-            return False
-
-        # 4. Verify — raises InvalidSignature on failure
-        pub_key.verify(sig_bytes, message, ec.ECDSA(hashes.SHA256()))
-        return True
-
-    except Exception as e:
-        print(f"[ADMOB] Signature verification failed: {e}")
-        return False
-
-
-@app.route('/api/admob/callback', methods=['GET'])
-def admob_callback():
-    """
-    Google AdMob SSV callback — called server-to-server when a rewarded ad completes.
-    The Android client never touches this endpoint; Google calls it directly.
-
-    custom_data (JSON, set by the app before showing the ad):
-      { "device_id": "...", "public_key": "...", "ad_type": "main_ad"|"bonus_ad" }
-    """
-    try:
-        # ======================================================================
-        # ⚠️ ADMOB BYPASS (TEMPORARY FOR APP REVIEW)
-        # DELETE THIS ENTIRE BLOCK WHEN YOU WANT TO ENABLE REAL ADS
-        # ======================================================================
-        custom_data_str = request.args.get('custom_data')
-        if not custom_data_str:
-            return "OK", 200
-        # ======================================================================
-
-        # ======================================================================
-        # ✅ REAL ADMOB CODE
-        # UNCOMMENT THIS ENTIRE BLOCK WHEN YOU WANT TO ENABLE REAL ADS
-        # ======================================================================
-        # signature       = request.args.get('signature')
-        # key_id          = request.args.get('key_id')
-        # custom_data_str = request.args.get('custom_data')
-        # 
-        # # Google sends a verification ping with signature+key_id but no custom_data
-        # if not custom_data_str:
-        #     return "OK", 200  # Verification ping from Google dashboard
-        # 
-        # if not all([signature, key_id]):
-        #     return "Missing parameters", 400
-        # 
-        # raw_qs = request.query_string.decode("utf-8")
-        # if not _verify_admob_signature(raw_qs, signature, key_id):
-        #     print("[ADMOB] Rejected callback — invalid signature.")
-        #     return "Forbidden", 403
-        # ======================================================================
-
-        custom_data   = json.loads(custom_data_str)
-        device_id     = custom_data.get('device_id')
-        client_pubkey = custom_data.get('public_key')
-        
-        if not device_id or not client_pubkey:
-            return "Invalid custom_data payload", 400
-
-        ad_type       = custom_data.get('ad_type', 'main_ad')
-
-        success, msg = _start_or_extend_session(device_id, client_pubkey, ad_type)
-        return ("OK", 200) if success else (msg, 500)
-
-    except Exception as e:
-        print(f"[ADMOB] SSV Error: {e}")
-        return "Internal Error", 500
-
-
-# ==============================================================================
-# FLASK API (APP POLLING)
-# ==============================================================================
-
-@app.route('/api/session/status', methods=['GET'])
-def session_status():
-    """
-    Query: ?device_id=esf-xxx
-    Returns current session state so the Android app can construct its AmneziaWG config.
-    """
-    device_id = request.args.get('device_id')
-    if not device_id:
-        return jsonify({"error": "Missing query parameter: device_id"}), 400
-
-    with sessions_lock:
-        session = active_sessions.get(device_id)
-
-    if not session:
-        return jsonify({"active": False, "message": "No session found."}), 404
-
-    # Bulletproof fallback: If server public key is missing, try fetching it right now
-    global SERVER_PUBKEY
-    if not SERVER_PUBKEY:
-        pubkey = run_cmd("awg show awg0 public-key")
-        if pubkey:
-            SERVER_PUBKEY = pubkey
-            print(f"[AWG] Dynamic Server Public Key cached from awg0: {SERVER_PUBKEY}")
-        else:
-            SERVER_PUBKEY = SERVER_PUBKEY_FALLBACK or "server key="
-
-    stats          = get_wireguard_stats()
-    current_bytes  = stats.get(session["ip"], {}).get("total_bytes", 0)
-    used_bytes     = max(0, current_bytes - session["baseline_bytes"])
-    remaining_data = max(0, session["quota_bytes"] - used_bytes)
-    remaining_secs = max(0, session["expires_at"] - time.time())
-
-    return jsonify({
-        "active":             remaining_secs > 0,
-        "client_ip":          session["ip"],
-        "client_ipv6":        session.get("ipv6", ""),
-        "server_pubkey":      SERVER_PUBKEY,
-        "is_throttled":       session["is_throttled"],
-        "expires_in_seconds": int(remaining_secs),
-        "quota_bytes":        session["quota_bytes"],
-        "used_bytes":         used_bytes,
-        "remaining_bytes":    remaining_data,
-    })
-
-
-@app.route('/api/session/stop', methods=['POST'])
-def session_stop():
-    """Allows the app to explicitly tear down its session on disconnect."""
-    data = request.get_json(silent=True)
-    device_id = data.get('device_id') if data else None
-    
-    if device_id:
-        with sessions_lock:
-            session = active_sessions.pop(device_id, None)
-            if session:
-                remove_wg_peer(session["pubkey"])
-                if session["is_throttled"]:
-                    remove_throttle(session["ip"])
-                release_ip(session["ip"])
-                print(f"[API] Explicit stop for {device_id}.")
-                
-    return jsonify({"success": True})
-
-
 # ==============================================================================
 # ENTRY POINT
 # ==============================================================================