Fix IT2Me protocol error connecting to old hosts.

remoting/protocol/negotiating_client_authenticator.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 "remoting/protocol/negotiating_client_authenticator.h"
 
 #include <algorithm>
 #include <sstream>
 #include <utility>
 
@@ skipping 24 matching lines @@
   if (!config_.fetch_third_party_token_callback.is_null()) {
     AddMethod(Method::THIRD_PARTY_SPAKE2_CURVE25519);
     AddMethod(Method::THIRD_PARTY_SPAKE2_P224);
   }
 
   AddMethod(Method::PAIRED_SPAKE2_CURVE25519);
   AddMethod(Method::PAIRED_SPAKE2_P224);
 
   AddMethod(Method::SHARED_SECRET_SPAKE2_CURVE25519);
   AddMethod(Method::SHARED_SECRET_SPAKE2_P224);
+
+  AddMethod(Method::SHARED_SECRET_PLAIN_SPAKE2_P224);
 }
 
 NegotiatingClientAuthenticator::~NegotiatingClientAuthenticator() {}
 
 void NegotiatingClientAuthenticator::ProcessMessage(
     const buzz::XmlElement* message,
     const base::Closure& resume_callback) {
   DCHECK_EQ(state(), WAITING_MESSAGE);
   state_ = PROCESSING_MESSAGE;
 
@@ skipping 102 matching lines @@
     case Method::PAIRED_SPAKE2_CURVE25519: {
       PairingClientAuthenticator* pairing_authenticator =
           new PairingClientAuthenticator(
               config_, base::Bind(&Spake2Authenticator::CreateForClient,
                                   local_id_, remote_id_));
       current_authenticator_ = base::WrapUnique(pairing_authenticator);
       pairing_authenticator->Start(preferred_initial_state, resume_callback);
       break;
     }
 
+    case Method::SHARED_SECRET_PLAIN_SPAKE2_P224:
     case Method::SHARED_SECRET_SPAKE2_P224:
     case Method::SHARED_SECRET_SPAKE2_CURVE25519:
       config_.fetch_secret_callback.Run(
           false,
           base::Bind(
               &NegotiatingClientAuthenticator::CreateSharedSecretAuthenticator,
               weak_factory_.GetWeakPtr(), preferred_initial_state,
               resume_callback));
       break;
   }
@@ skipping 10 matching lines @@
     pairing_authenticator->StartPaired(MESSAGE_READY);
     current_method_ = Method::PAIRED_SPAKE2_P224;
   }
 }
 
 void NegotiatingClientAuthenticator::CreateSharedSecretAuthenticator(
     Authenticator::State initial_state,
     const base::Closure& resume_callback,
     const std::string& shared_secret) {
   std::string shared_secret_hash =
-      GetSharedSecretHash(config_.host_id, shared_secret);
+      (current_method_ == Method::SHARED_SECRET_PLAIN_SPAKE2_P224)
+          ? shared_secret
+          : GetSharedSecretHash(config_.host_id, shared_secret);
+
   if (current_method_ == Method::SHARED_SECRET_SPAKE2_CURVE25519) {
     current_authenticator_ = Spake2Authenticator::CreateForClient(
         local_id_, remote_id_, shared_secret_hash, initial_state);
   } else {
     current_authenticator_ =
         V2Authenticator::CreateForClient(shared_secret_hash, initial_state);
   }
   resume_callback.Run();
 }
 
 bool NegotiatingClientAuthenticator::is_paired() {
   return !config_.pairing_client_id.empty() && !config_.pairing_secret.empty();
 }
 
 }  // namespace protocol
 }  // namespace remoting