Fake TLS: mirror client key share and profile the masking site (#1473)

proxy/tg_ws_proxy.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 import os
 import sys
 import time
+import random
 import struct
 import asyncio
 import hashlib
@@ -24,7 +25,11 @@ from .stats import stats
 from .config import proxy_config, parse_dc_ip_list, start_cfproxy_domain_refresh, coerce_domain_list
 from .bridge import MsgSplitter, CryptoCtx, do_fallback, bridge_ws_reencrypt, reset_tcp_backoff
 from .raw_websocket import set_sock_opts
-from .fake_tls import proxy_to_masking_domain, verify_client_hello, build_server_hello, FakeTlsStream, TLS_RECORD_HANDSHAKE
+from .fake_tls import (
+    proxy_to_masking_domain, verify_client_hello, parse_client_hello, build_server_hello,
+    probe_appdata_len, set_profiled_appdata_len, FakeTlsStream, TLS_RECORD_HANDSHAKE,
+    SERVER_HELLO_DELAY,
+)
 from .balancer import balancer
 from .pool import ws_pool, cf_worker_pool
 from .cf_h2 import CfH2Pool
@@ -162,7 +167,9 @@ async def _read_client_init(reader, writer, secret, label, masking):
         client_random, session_id, ts = tls_result
         log.debug("[%s] Fake TLS handshake ok (ts=%d)", label, ts)
 
-        server_hello = build_server_hello(secret, client_random, session_id)
+        server_hello = build_server_hello(
+            secret, client_random, session_id, parse_client_hello(client_hello))
+        await asyncio.sleep(random.uniform(*SERVER_HELLO_DELAY))
         writer.write(server_hello)
         await writer.drain()
 
@@ -379,6 +386,19 @@ async def _run(stop_event: Optional[asyncio.Event] = None):
     secret_bytes = bytes.fromhex(proxy_config.secret)
     stopping = False
 
+    # Probe before listening so a domain that resolves to this proxy fails
+    # fast instead of answering itself
+    set_profiled_appdata_len(None)
+    if proxy_config.fake_tls_domain:
+        appdata_len = await probe_appdata_len(proxy_config.fake_tls_domain)
+        set_profiled_appdata_len(appdata_len)
+        if appdata_len is None:
+            log.warning("Fake TLS profile unavailable, ServerHello uses "
+                        "random record sizes")
+        else:
+            log.info("Fake TLS profile: first encrypted record %d bytes",
+                     appdata_len)
+
     def client_cb(r, w):
         if stopping:
             w.close()