Restore win7 compatability

proxy/fake_tls.py

@@ -12,6 +12,7 @@ import logging
 
 from typing import Dict, FrozenSet, NamedTuple, Optional, Tuple
 from .stats import stats
+from .utils import set_x25519
 
 try:
     from cryptography.hazmat.primitives.asymmetric.x25519 import X25519PrivateKey
@@ -272,7 +273,7 @@ async def probe_appdata_len(domain: str, port: int = 443,
     writer = None
     try:
         ctx = ssl.create_default_context()
-        ctx.set_ecdh_curve('X25519')
+        set_x25519(ctx)
         ctx.check_hostname = False
         ctx.verify_mode = ssl.CERT_NONE
         ctx.minimum_version = ssl.TLSVersion.TLSv1_3

proxy/utils.py

@@ -143,13 +143,20 @@ class _PinnedHTTPSHandler(urllib.request.HTTPSHandler):
             return super().https_open(req)
 
 
+def set_x25519(context: ssl.SSLContext) -> None:
+    try:
+        context.set_ecdh_curve('X25519')
+    except Exception:
+        pass
+
+
 def create_ssl_context(*, check_hostname: bool = True) -> ssl.SSLContext:
     bundle_dir = getattr(sys, '_MEIPASS', None)
     cafile = (os.path.join(bundle_dir, 'certifi', 'cacert.pem')
               if bundle_dir else certifi.where())
     context = ssl.create_default_context(cafile=cafile)
     context.load_default_certs()
-    context.set_ecdh_curve('X25519')
+    set_x25519(context)
     context.check_hostname = check_hostname
     return context