relnote: Disables strike register lookups when talking QUIC_VERSION_27

net/quic/crypto/quic_crypto_server_config.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/quic/crypto/quic_crypto_server_config.h"
 
 #include <stdlib.h>
 #include <algorithm>
 
 #include "base/stl_util.h"
@@ skipping 1022 matching lines @@
     info->reject_reasons.push_back(CLIENT_NONCE_INVALID_FAILURE);
     // Invalid client nonce.
     DVLOG(1) << "Invalid client nonce.";
     if (FLAGS_use_early_return_when_verifying_chlo) {
       helper.ValidationComplete(QUIC_NO_ERROR, "");
       return;
     }
     found_error = true;
   }
 
+  // Server nonce is optional, and used for key derivation if present.
+  client_hello.GetStringPiece(kServerNonceTag, &info->server_nonce);
+
+  if (version > QUIC_VERSION_26) {
+    DVLOG(1) << "No 0-RTT replay protection in QUIC_VERSION_27 and higher.";
+    // If the server nonce is empty and we're requiring handshake confirmation
+    // for DoS reasons then we must reject the CHLO.
+    if (FLAGS_quic_require_handshake_confirmation &&
+        info->server_nonce.empty()) {
+      info->reject_reasons.push_back(SERVER_NONCE_REQUIRED_FAILURE);
+    }
+    helper.ValidationComplete(QUIC_NO_ERROR, "");
+    return;
+  }
+
   if (!replay_protection_) {
     DVLOG(1) << "No replay protection.";
     helper.ValidationComplete(QUIC_NO_ERROR, "");
     return;
   }
 
-  client_hello.GetStringPiece(kServerNonceTag, &info->server_nonce);
   if (!info->server_nonce.empty()) {
     // If the server nonce is present, use it to establish uniqueness.
     HandshakeFailureReason server_nonce_error =
         ValidateServerNonce(info->server_nonce, info->now);
     bool is_unique = server_nonce_error == HANDSHAKE_OK;
     if (!is_unique) {
       info->reject_reasons.push_back(server_nonce_error);
     }
     DVLOG(1) << "Using server nonce, unique: " << is_unique;
     helper.ValidationComplete(QUIC_NO_ERROR, "");
@@ skipping 632 matching lines @@
 QuicCryptoServerConfig::Config::Config()
     : channel_id_enabled(false),
       is_primary(false),
       primary_time(QuicWallTime::Zero()),
       priority(0),
       source_address_token_boxer(nullptr) {}
 
 QuicCryptoServerConfig::Config::~Config() { STLDeleteElements(&key_exchanges); }
 
 }  // namespace net