diff --git a/app/api/routers/monitor.py b/app/api/routers/monitor.py
index 6c37a14..1435e6f 100644
--- a/app/api/routers/monitor.py
+++ b/app/api/routers/monitor.py
@@ -23,6 +23,7 @@ from app.services.monitoring import (
     get_server_states_view,
     test_provider_connection,
 )
+from app.services.crypto_box import get_public_key_info, decrypt_payload_b64, ts_within
 
 router = APIRouter(prefix='/monitor', tags=['Monitor'])
 SUPPORTED_PROVIDERS = {'anthropic', 'openai', 'minimax', 'kimi', 'qwen'}
@@ -57,6 +58,11 @@ def require_admin(current_user: models.User = Depends(get_current_user_or_apikey
     return current_user
 
 
+@router.get('/public/server-public-key')
+def monitor_public_key():
+    return get_public_key_info()
+
+
 @router.get('/public/overview')
 def public_overview(db: Session = Depends(get_db)):
     return {
@@ -202,9 +208,22 @@ async def server_ws(websocket: WebSocket):
     server_id = None
     try:
         hello = await websocket.receive_json()
-        identifier = (hello.get('identifier') or '').strip()
-        challenge_uuid = (hello.get('challenge_uuid') or '').strip()
-        nonce = (hello.get('nonce') or '').strip()
+
+        encrypted_payload = (hello.get('encrypted_payload') or '').strip()
+        if encrypted_payload:
+            data = decrypt_payload_b64(encrypted_payload)
+            identifier = (data.get('identifier') or '').strip()
+            challenge_uuid = (data.get('challenge_uuid') or '').strip()
+            nonce = (data.get('nonce') or '').strip()
+            ts = data.get('ts')
+            if not ts_within(ts, max_minutes=10):
+                await websocket.close(code=4401)
+                return
+        else:
+            # backward compatible mode
+            identifier = (hello.get('identifier') or '').strip()
+            challenge_uuid = (hello.get('challenge_uuid') or '').strip()
+            nonce = (hello.get('nonce') or '').strip()
 
         if not identifier or not challenge_uuid or not nonce:
             await websocket.close(code=4400)
diff --git a/app/services/crypto_box.py b/app/services/crypto_box.py
new file mode 100644
index 0000000..38423ba
--- /dev/null
+++ b/app/services/crypto_box.py
@@ -0,0 +1,63 @@
+import base64
+import hashlib
+import json
+import os
+from datetime import datetime, timezone
+from pathlib import Path
+from typing import Dict, Any
+
+from cryptography.hazmat.primitives import serialization, hashes
+from cryptography.hazmat.primitives.asymmetric import rsa, padding
+
+KEY_DIR = Path(os.getenv('MONITOR_KEY_DIR', '/config/monitor_keys'))
+PRIV_PATH = KEY_DIR / 'monitor_private.pem'
+PUB_PATH = KEY_DIR / 'monitor_public.pem'
+
+
+def ensure_keypair() -> None:
+    KEY_DIR.mkdir(parents=True, exist_ok=True)
+    if PRIV_PATH.exists() and PUB_PATH.exists():
+        return
+    private_key = rsa.generate_private_key(public_exponent=65537, key_size=2048)
+    private_pem = private_key.private_bytes(
+        encoding=serialization.Encoding.PEM,
+        format=serialization.PrivateFormat.TraditionalOpenSSL,
+        encryption_algorithm=serialization.NoEncryption(),
+    )
+    public_pem = private_key.public_key().public_bytes(
+        encoding=serialization.Encoding.PEM,
+        format=serialization.PublicFormat.SubjectPublicKeyInfo,
+    )
+    PRIV_PATH.write_bytes(private_pem)
+    PUB_PATH.write_bytes(public_pem)
+
+
+def get_public_key_info() -> Dict[str, str]:
+    ensure_keypair()
+    pem = PUB_PATH.read_text()
+    kid = hashlib.sha256(pem.encode()).hexdigest()[:16]
+    return {'public_key_pem': pem, 'key_id': kid}
+
+
+def decrypt_payload_b64(ciphertext_b64: str) -> Dict[str, Any]:
+    ensure_keypair()
+    private_key = serialization.load_pem_private_key(PRIV_PATH.read_bytes(), password=None)
+    plaintext = private_key.decrypt(
+        base64.b64decode(ciphertext_b64),
+        padding.OAEP(
+            mgf=padding.MGF1(algorithm=hashes.SHA256()),
+            algorithm=hashes.SHA256(),
+            label=None,
+        ),
+    )
+    obj = json.loads(plaintext.decode())
+    return obj
+
+
+def ts_within(ts_iso: str, max_minutes: int = 10) -> bool:
+    try:
+        ts = datetime.fromisoformat(ts_iso.replace('Z', '+00:00'))
+    except Exception:
+        return False
+    now = datetime.now(timezone.utc)
+    return abs((now - ts).total_seconds()) <= max_minutes * 60