gh-109945: Enable spec of multiple curves/groups for TLS

Doc/library/ssl.rst

@@ -1769,6 +1769,10 @@ to speed up repeated connections from the same clients.
  a well-known elliptic curve, for example ``prime256v1`` for a widely
  supported curve.
 
+ For OpenSSL 3.0 and above *curve_name* parameter can be a colon separated
+ list of curves, for example ``prime256v1:brainpoolP384r1`` specifies two curves that will be
+ used on a client hello.
+
  This setting doesn't apply to client sockets. You can also use the
  :data:`OP_SINGLE_ECDH_USE` option to further improve security.
 

Lib/test/test_ssl.py

@@ -1375,11 +1375,29 @@ def test_set_ecdh_curve(self):
  ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
  ctx.set_ecdh_curve("prime256v1")
  ctx.set_ecdh_curve(b"prime256v1")
+ # Only OpenSSL 3 and above supported for multiple curves
+ if (IS_OPENSSL_3_0_0 >= 3):
+ ctx.set_ecdh_curve("prime256v1:brainpoolP384r1")
+ ctx.set_ecdh_curve(b"prime256v1:brainpoolP384r1")
  self.assertRaises(TypeError, ctx.set_ecdh_curve)
  self.assertRaises(TypeError, ctx.set_ecdh_curve, None)
  self.assertRaises(ValueError, ctx.set_ecdh_curve, "foo")
  self.assertRaises(ValueError, ctx.set_ecdh_curve, b"foo")
-
+ # Multiple bad curves should cause error for any OpenSSL version
+ self.assertRaises(ValueError, ctx.set_ecdh_curve, "foo:bar")
+ self.assertRaises(ValueError, ctx.set_ecdh_curve, b"foo:bar")
+ self.assertRaises(ValueError, ctx.set_ecdh_curve, "prime256v1:bar")
+ self.assertRaises(ValueError, ctx.set_ecdh_curve, b"prime256v1:bar")
+ self.assertRaises(ValueError, ctx.set_ecdh_curve, "foo:prime256v1")
+ self.assertRaises(ValueError, ctx.set_ecdh_curve, b"foo:prime256v1")
+ #self.assertRaises(ValueError, ctx.set_ecdh_curve, ":")
+ #self.assertRaises(ValueError, ctx.set_ecdh_curve, b":")
+ #self.assertRaises(ValueError, ctx.set_ecdh_curve, "::")
+ #self.assertRaises(ValueError, ctx.set_ecdh_curve, b"::")
+ #self.assertRaises(ValueError, ctx.set_ecdh_curve, "prime256v1:")
+ #self.assertRaises(ValueError, ctx.set_ecdh_curve, b"prime256v1:")
+ #self.assertRaises(ValueError, ctx.set_ecdh_curve, ":prime256v1")
+ #self.assertRaises(ValueError, ctx.set_ecdh_curve, b":prime256v1")
  def test_sni_callback(self):
  ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
 

Misc/NEWS.d/next/Library/2024-06-04-07-28-18.gh-issue-109945.02TejW.rst

@@ -0,0 +1 @@
+Adds support for multiple curves to be specified in SSLContext.set_ecdh_curve() for OpenSSL 3.0 and above by setting curve_name to a colon separated list of curves. This allows multiple curves to be passed on a TLS client hello.

Modules/_ssl.c

@@ -4379,18 +4379,19 @@ _ssl__SSLContext_set_ecdh_curve(PySSLContext *self, PyObject *name)
 /*[clinic end generated code: output=23022c196e40d7d2 input=c2bafb6f6e34726b]*/
 {
  PyObject *name_bytes;
- int nid;
+
  if (!PyUnicode_FSConverter(name, &name_bytes))
  return NULL;
  assert(PyBytes_Check(name_bytes));
+#if OPENSSL_VERSION_MAJOR < 3
+ int nid;
  nid = OBJ_sn2nid(PyBytes_AS_STRING(name_bytes));
  Py_DECREF(name_bytes);
  if (nid == 0){
  PyErr_Format(PyExc_ValueError,
  "unknown elliptic curve name %R", name);
  return NULL;
  }
-#if OPENSSL_VERSION_MAJOR < 3
  EC_KEY *key = EC_KEY_new_by_curve_name(nid);
  if (key == NULL){
  _setSSLError(get_state_ctx(self), NULL, 0, __FILE__, __LINE__);
@@ -4399,8 +4400,10 @@ _ssl__SSLContext_set_ecdh_curve(PySSLContext *self, PyObject *name)
  SSL_CTX_set_tmp_ecdh(self->ctx, key);
  EC_KEY_free(key);
 #else
- if (!SSL_CTX_set1_groups(self->ctx, &nid, 1)){
- _setSSLError(get_state_ctx(self), NULL, 0, __FILE__, __LINE__);
+ int res = SSL_CTX_set1_groups_list(self->ctx, PyBytes_AS_STRING(name_bytes));
+ Py_DECREF(name_bytes);
+ if (!res){
+ PyErr_Format(PyExc_ValueError,"unknown elliptic curves %R", name);
  return NULL;
  }
 #endif