10 files changed, 522 insertions, 42 deletions

diff --git a/remoting/protocol/authentication_method.cc b/remoting/protocol/authentication_method.cc
index ebee009..0082126 100644
--- a/remoting/protocol/authentication_method.cc
+++ b/remoting/protocol/authentication_method.cc
@@ -42,25 +42,12 @@ AuthenticationMethod AuthenticationMethod::FromString(
   }
 }
 
-AuthenticationMethod::AuthenticationMethod()
-    : invalid_(true),
-      version_(VERSION_2),
-      hash_function_(NONE) {
-}
-
-AuthenticationMethod::AuthenticationMethod(Version version,
-                                           HashFunction hash_function)
-    : invalid_(false),
-      version_(version),
-      hash_function_(hash_function) {
-}
-
+// static
 std::string AuthenticationMethod::ApplyHashFunction(
+    HashFunction hash_function,
     const std::string& tag,
     const std::string& shared_secret) {
-  DCHECK(is_valid());
-
-  switch (hash_function_) {
+  switch (hash_function) {
     case NONE:
       return shared_secret;
       break;
@@ -84,10 +71,23 @@ std::string AuthenticationMethod::ApplyHashFunction(
   return shared_secret;
 }
 
+AuthenticationMethod::AuthenticationMethod()
+    : invalid_(true),
+      version_(VERSION_2),
+      hash_function_(NONE) {
+}
+
+AuthenticationMethod::AuthenticationMethod(Version version,
+                                           HashFunction hash_function)
+    : invalid_(false),
+      version_(version),
+      hash_function_(hash_function) {
+}
+
 scoped_ptr<Authenticator> AuthenticationMethod::CreateAuthenticator(
     const std::string& local_jid,
     const std::string& tag,
-    const std::string& shared_secret) {
+    const std::string& shared_secret) const {
   DCHECK(is_valid());
 
   switch (version_) {
@@ -98,7 +98,8 @@ scoped_ptr<Authenticator> AuthenticationMethod::CreateAuthenticator(
 
     case VERSION_2:
       return protocol::V2Authenticator::CreateForClient(
-          ApplyHashFunction(tag, shared_secret));
+          ApplyHashFunction(hash_function_, tag, shared_secret),
+          Authenticator::MESSAGE_READY);
   }
 
   NOTREACHED();
@@ -135,5 +136,15 @@ const std::string AuthenticationMethod::ToString() const {
   return "";
 }
 
+bool AuthenticationMethod::operator ==(
+    const AuthenticationMethod& other) const {
+  if (!is_valid())
+    return !other.is_valid();
+  if (!other.is_valid())
+    return false;
+  return version_ == other.version_ &&
+      hash_function_ == other.hash_function_;
+}
+
 }  // namespace protocol
 }  // namespace remoting
diff --git a/remoting/protocol/authentication_method.h b/remoting/protocol/authentication_method.h
index 402e3bc..6b94a06 100644
--- a/remoting/protocol/authentication_method.h
+++ b/remoting/protocol/authentication_method.h
@@ -49,6 +49,12 @@ class AuthenticationMethod {
   // invalid value if the string is invalid.
   static AuthenticationMethod FromString(const std::string& value);
 
+  // Applies the specified hash function to |shared_secret| with the
+  // specified |tag| as a key.
+  static std::string ApplyHashFunction(HashFunction hash_function,
+                                       const std::string& tag,
+                                       const std::string& shared_secret);
+
   // Returns true
   bool is_valid() const { return !invalid_; }
 
@@ -63,16 +69,18 @@ class AuthenticationMethod {
   // Returns string representation of the value stored in this object.
   const std::string ToString() const;
 
-  // Applies the current hash function to |shared_secret| with the
-  // specified |tag| as a key.
-  std::string ApplyHashFunction(const std::string& tag,
-                                const std::string& shared_secret);
-
   // Creates client authenticator using the specified parameters.
   scoped_ptr<Authenticator> CreateAuthenticator(
       const std::string& local_jid,
       const std::string& tag,
-      const std::string& shared_secret);
+      const std::string& shared_secret) const;
+
+  // Comparison operators so that std::find() can be used with
+  // collections of this class.
+  bool operator ==(const AuthenticationMethod& other) const;
+  bool operator !=(const AuthenticationMethod& other) const {
+    return !(*this == other);
+  }
 
  private:
   AuthenticationMethod();
diff --git a/remoting/protocol/me2me_host_authenticator_factory.cc b/remoting/protocol/me2me_host_authenticator_factory.cc
index c4c6052..21272cf 100644
--- a/remoting/protocol/me2me_host_authenticator_factory.cc
+++ b/remoting/protocol/me2me_host_authenticator_factory.cc
@@ -109,7 +109,8 @@ scoped_ptr<Authenticator> Me2MeHostAuthenticatorFactory::CreateAuthenticator(
 
   if (V2Authenticator::IsEkeMessage(first_message)) {
     return V2Authenticator::CreateForHost(
-        local_cert_, *local_private_key_, shared_secret_hash_.value);
+        local_cert_, *local_private_key_, shared_secret_hash_.value,
+        Authenticator::WAITING_MESSAGE);
   }
 
   // TODO(sergeyu): Old clients still use V1 auth protocol. Remove
diff --git a/remoting/protocol/negotiating_authenticator.cc b/remoting/protocol/negotiating_authenticator.cc
new file mode 100644
index 0000000..55e1d78
--- /dev/null
+++ b/remoting/protocol/negotiating_authenticator.cc
@@ -0,0 +1,223 @@
+// Copyright (c) 2012 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_authenticator.h"
+
+#include <algorithm>
+#include <sstream>
+
+#include "base/logging.h"
+#include "base/string_split.h"
+#include "crypto/rsa_private_key.h"
+#include "remoting/protocol/channel_authenticator.h"
+#include "remoting/protocol/v2_authenticator.h"
+#include "third_party/libjingle/source/talk/xmllite/xmlelement.h"
+
+namespace remoting {
+namespace protocol {
+
+namespace {
+
+const buzz::StaticQName kMethodAttributeQName = { "", "method" };
+const buzz::StaticQName kSupportedMethodsAttributeQName =
+    { "", "supported-methods" };
+
+const char kSupportedMethodsSeparator = ',';
+
+}  // namespace
+
+// static
+scoped_ptr<Authenticator> NegotiatingAuthenticator::CreateForClient(
+    const std::string& authentication_tag,
+    const std::string& shared_secret,
+    const std::vector<AuthenticationMethod>& methods) {
+  scoped_ptr<NegotiatingAuthenticator> result(
+      new NegotiatingAuthenticator(MESSAGE_READY));
+  result->authentication_tag_ = authentication_tag;
+  result->shared_secret_ = shared_secret;
+
+  DCHECK(!methods.empty());
+  for (std::vector<AuthenticationMethod>::const_iterator it = methods.begin();
+       it != methods.end(); ++it) {
+    result->AddMethod(*it);
+  }
+
+  return scoped_ptr<Authenticator>(result.Pass());
+}
+
+// static
+scoped_ptr<Authenticator> NegotiatingAuthenticator::CreateForHost(
+    const std::string& local_cert,
+    const crypto::RSAPrivateKey& local_private_key,
+    const std::string& shared_secret_hash,
+    AuthenticationMethod::HashFunction hash_function) {
+  scoped_ptr<NegotiatingAuthenticator> result(
+      new NegotiatingAuthenticator(WAITING_MESSAGE));
+  result->local_cert_ = local_cert;
+  result->local_private_key_.reset(local_private_key.Copy());
+  result->shared_secret_hash_ = shared_secret_hash;
+
+  result->AddMethod(AuthenticationMethod::Spake2(hash_function));
+
+  return scoped_ptr<Authenticator>(result.Pass());
+}
+
+
+NegotiatingAuthenticator::NegotiatingAuthenticator(
+    Authenticator::State initial_state)
+    : current_method_(AuthenticationMethod::Invalid()),
+      state_(initial_state),
+      rejection_reason_(INVALID_CREDENTIALS) {
+}
+
+NegotiatingAuthenticator::~NegotiatingAuthenticator() {
+}
+
+Authenticator::State NegotiatingAuthenticator::state() const {
+  return state_;
+}
+
+Authenticator::RejectionReason
+NegotiatingAuthenticator::rejection_reason() const {
+  return rejection_reason_;
+}
+
+void NegotiatingAuthenticator::ProcessMessage(const buzz::XmlElement* message) {
+  DCHECK_EQ(state(), WAITING_MESSAGE);
+
+  std::string method_attr = message->Attr(kMethodAttributeQName);
+  AuthenticationMethod method = AuthenticationMethod::FromString(method_attr);
+
+  // Check if the remote end specified a method that is not supported locally.
+  if (method.is_valid() &&
+      std::find(methods_.begin(), methods_.end(), method) == methods_.end()) {
+    method = AuthenticationMethod::Invalid();
+  }
+
+  // If the remote peer did not specify auth method or specified unknown
+  // method then select the first known method from the supported-methods
+  // attribute.
+  if (!method.is_valid()) {
+    std::string supported_methods_attr =
+        message->Attr(kSupportedMethodsAttributeQName);
+    if (supported_methods_attr.empty()) {
+      // Message contains neither method nor supported-methods attributes.
+      state_ = REJECTED;
+      rejection_reason_ = PROTOCOL_ERROR;
+      return;
+    }
+
+    // Find the first mutually-supported method in the peer's list of
+    // supported-methods.
+    std::vector<std::string> supported_methods_strs;
+    base::SplitString(supported_methods_attr, kSupportedMethodsSeparator,
+                      &supported_methods_strs);
+    for (std::vector<std::string>::iterator it = supported_methods_strs.begin();
+         it != supported_methods_strs.end(); ++it) {
+      AuthenticationMethod list_value = AuthenticationMethod::FromString(*it);
+      if (list_value.is_valid() &&
+          std::find(methods_.begin(),
+                    methods_.end(), list_value) != methods_.end()) {
+        // Found common method.
+        method = list_value;
+        break;
+      }
+    }
+
+    if (!method.is_valid()) {
+      // Failed to find a common auth method.
+      state_ = REJECTED;
+      rejection_reason_ = PROTOCOL_ERROR;
+      return;
+    }
+
+    // Drop the current message because we've chosen a different
+    // method.
+    state_ = MESSAGE_READY;
+  }
+
+  DCHECK(method.is_valid());
+
+  // Replace current authenticator if the method has changed.
+  if (method != current_method_) {
+    current_method_ = method;
+    CreateAuthenticator(state_);
+  }
+
+  if (state_ == WAITING_MESSAGE) {
+    current_authenticator_->ProcessMessage(message);
+    state_ = current_authenticator_->state();
+    if (state_ == REJECTED)
+      rejection_reason_ = current_authenticator_->rejection_reason();
+  }
+}
+
+scoped_ptr<buzz::XmlElement> NegotiatingAuthenticator::GetNextMessage() {
+  DCHECK_EQ(state(), MESSAGE_READY);
+
+  bool add_supported_methods_attr = false;
+
+  // Initialize current method in case it is not initialized
+  // yet. Normally happens only on client.
+  if (!current_method_.is_valid()) {
+    CHECK(!methods_.empty());
+
+    // Initially try the first method.
+    current_method_ = methods_[0];
+    CreateAuthenticator(MESSAGE_READY);
+    add_supported_methods_attr = true;
+  }
+
+  scoped_ptr<buzz::XmlElement> result =
+      current_authenticator_->GetNextMessage();
+  state_ = current_authenticator_->state();
+  DCHECK_NE(state_, REJECTED);
+
+  result->AddAttr(kMethodAttributeQName, current_method_.ToString());
+
+  if (add_supported_methods_attr) {
+    std::stringstream supported_methods(std::stringstream::out);
+    for (std::vector<AuthenticationMethod>::iterator it = methods_.begin();
+         it != methods_.end(); ++it) {
+      if (it != methods_.begin())
+        supported_methods << kSupportedMethodsSeparator;
+      supported_methods << it->ToString();
+    }
+    result->AddAttr(kSupportedMethodsAttributeQName, supported_methods.str());
+  }
+
+  return result.Pass();
+}
+
+void NegotiatingAuthenticator::AddMethod(const AuthenticationMethod& method) {
+  DCHECK(method.is_valid());
+  methods_.push_back(method);
+}
+
+scoped_ptr<ChannelAuthenticator>
+NegotiatingAuthenticator::CreateChannelAuthenticator() const {
+  DCHECK_EQ(state(), ACCEPTED);
+  return current_authenticator_->CreateChannelAuthenticator();
+}
+
+bool NegotiatingAuthenticator::is_host_side() const {
+  return local_private_key_.get() != NULL;
+}
+
+void NegotiatingAuthenticator::CreateAuthenticator(State initial_state) {
+  if (is_host_side()) {
+    current_authenticator_ = V2Authenticator::CreateForHost(
+        local_cert_, *local_private_key_.get(),
+        shared_secret_hash_, initial_state);
+  } else {
+    current_authenticator_ = V2Authenticator::CreateForClient(
+        AuthenticationMethod::ApplyHashFunction(
+            current_method_.hash_function(),
+            authentication_tag_, shared_secret_),
+        initial_state);
+  }
+}
+
+}  // namespace protocol
+}  // namespace remoting
diff --git a/remoting/protocol/negotiating_authenticator.h b/remoting/protocol/negotiating_authenticator.h
new file mode 100644
index 0000000..beda194
--- /dev/null
+++ b/remoting/protocol/negotiating_authenticator.h
@@ -0,0 +1,77 @@
+// Copyright (c) 2012 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.
+
+#ifndef REMOTING_PROTOCOL_NEGOTIATING_AUTHENTICATOR_H_
+#define REMOTING_PROTOCOL_NEGOTIATING_AUTHENTICATOR_H_
+
+#include <string>
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
+#include "remoting/protocol/authenticator.h"
+#include "remoting/protocol/authentication_method.h"
+
+namespace crypto {
+class RSAPrivateKey;
+}  // namespace crypto
+
+namespace remoting {
+namespace protocol {
+
+class NegotiatingAuthenticator : public Authenticator {
+ public:
+  virtual ~NegotiatingAuthenticator();
+
+  static scoped_ptr<Authenticator> CreateForClient(
+      const std::string& authentication_tag,
+      const std::string& shared_secret,
+      const std::vector<AuthenticationMethod>& methods);
+
+  static scoped_ptr<Authenticator> CreateForHost(
+      const std::string& local_cert,
+      const crypto::RSAPrivateKey& local_private_key,
+      const std::string& shared_secret_hash,
+      AuthenticationMethod::HashFunction hash_function);
+
+  // Authenticator interface.
+  virtual State state() const OVERRIDE;
+  virtual RejectionReason rejection_reason() const OVERRIDE;
+  virtual void ProcessMessage(const buzz::XmlElement* message) OVERRIDE;
+  virtual scoped_ptr<buzz::XmlElement> GetNextMessage() OVERRIDE;
+  virtual scoped_ptr<ChannelAuthenticator>
+      CreateChannelAuthenticator() const OVERRIDE;
+
+ private:
+  NegotiatingAuthenticator(Authenticator::State initial_state);
+
+  void AddMethod(const AuthenticationMethod& method);
+  void CreateAuthenticator(State initial_state);
+  bool is_host_side() const;
+
+  // Used only for host authenticators.
+  std::string local_cert_;
+  scoped_ptr<crypto::RSAPrivateKey> local_private_key_;
+  bool certificate_sent_;
+  std::string shared_secret_hash_;
+
+  // Used only for client authenticators.
+  std::string remote_cert_;
+  std::string authentication_tag_;
+  std::string shared_secret_;
+
+  // Used for both host and client authenticators.
+  std::vector<AuthenticationMethod> methods_;
+  AuthenticationMethod current_method_;
+  scoped_ptr<Authenticator> current_authenticator_;
+  State state_;
+  RejectionReason rejection_reason_;
+
+  DISALLOW_COPY_AND_ASSIGN(NegotiatingAuthenticator);
+};
+
+}  // namespace protocol
+}  // namespace remoting
+
+#endif  // REMOTING_PROTOCOL_NEGOTIATING_AUTHENTICATOR_H_
diff --git a/remoting/protocol/negotiating_authenticator_unittest.cc b/remoting/protocol/negotiating_authenticator_unittest.cc
new file mode 100644
index 0000000..e62a8e3
--- /dev/null
+++ b/remoting/protocol/negotiating_authenticator_unittest.cc
@@ -0,0 +1,150 @@
+// Copyright (c) 2012 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_authenticator.h"
+
+#include "base/bind.h"
+#include "net/base/net_errors.h"
+#include "remoting/protocol/authenticator_test_base.h"
+#include "remoting/protocol/channel_authenticator.h"
+#include "remoting/protocol/connection_tester.h"
+#include "testing/gmock/include/gmock/gmock.h"
+#include "testing/gtest/include/gtest/gtest.h"
+#include "third_party/libjingle/source/talk/xmllite/xmlelement.h"
+
+using testing::_;
+using testing::DeleteArg;
+using testing::SaveArg;
+
+namespace remoting {
+namespace protocol {
+
+namespace {
+
+const int kMessageSize = 100;
+const int kMessages = 1;
+
+const char kTestHostId[] = "12345678910123456";
+
+const char kTestSharedSecret[] = "1234-1234-5678";
+const char kTestSharedSecretBad[] = "0000-0000-0001";
+
+}  // namespace
+
+class NegotiatingAuthenticatorTest : public AuthenticatorTestBase {
+ public:
+  NegotiatingAuthenticatorTest() {
+  }
+  virtual ~NegotiatingAuthenticatorTest() {
+  }
+
+ protected:
+  void InitAuthenticators(
+      const std::string& client_secret,
+      const std::string& host_secret,
+      AuthenticationMethod::HashFunction hash_function,
+      bool client_hmac_only) {
+    std::string host_secret_hash = AuthenticationMethod::ApplyHashFunction(
+        hash_function, kTestHostId, host_secret);
+    host_ = NegotiatingAuthenticator::CreateForHost(
+        host_cert_, *private_key_, host_secret_hash, hash_function);
+
+    std::vector<AuthenticationMethod> methods;
+    methods.push_back(AuthenticationMethod::Spake2(
+        AuthenticationMethod::HMAC_SHA256));
+    if (!client_hmac_only) {
+      methods.push_back(AuthenticationMethod::Spake2(
+          AuthenticationMethod::NONE));
+    }
+    client_ = NegotiatingAuthenticator::CreateForClient(
+        kTestHostId, client_secret, methods);
+  }
+
+  void VerifyRejected(Authenticator::RejectionReason reason) {
+    ASSERT_TRUE((client_->state() == Authenticator::REJECTED &&
+                 (client_->rejection_reason() == reason)) ||
+                (host_->state() == Authenticator::REJECTED &&
+                 (host_->rejection_reason() == reason)));
+  }
+
+  DISALLOW_COPY_AND_ASSIGN(NegotiatingAuthenticatorTest);
+};
+
+TEST_F(NegotiatingAuthenticatorTest, SuccessfulAuthHmac) {
+  ASSERT_NO_FATAL_FAILURE(InitAuthenticators(
+      kTestSharedSecret, kTestSharedSecret,
+      AuthenticationMethod::HMAC_SHA256, false));
+  ASSERT_NO_FATAL_FAILURE(RunAuthExchange());
+
+  ASSERT_EQ(Authenticator::ACCEPTED, host_->state());
+  ASSERT_EQ(Authenticator::ACCEPTED, client_->state());
+
+  client_auth_ = client_->CreateChannelAuthenticator();
+  host_auth_ = host_->CreateChannelAuthenticator();
+  RunChannelAuth(false);
+
+  EXPECT_TRUE(client_socket_.get() != NULL);
+  EXPECT_TRUE(host_socket_.get() != NULL);
+
+  StreamConnectionTester tester(host_socket_.get(), client_socket_.get(),
+                                kMessageSize, kMessages);
+
+  tester.Start();
+  message_loop_.Run();
+  tester.CheckResults();
+}
+
+TEST_F(NegotiatingAuthenticatorTest, SuccessfulAuthPlain) {
+  ASSERT_NO_FATAL_FAILURE(InitAuthenticators(
+      kTestSharedSecret, kTestSharedSecret,
+      AuthenticationMethod::NONE, false));
+  ASSERT_NO_FATAL_FAILURE(RunAuthExchange());
+
+  ASSERT_EQ(Authenticator::ACCEPTED, host_->state());
+  ASSERT_EQ(Authenticator::ACCEPTED, client_->state());
+
+  client_auth_ = client_->CreateChannelAuthenticator();
+  host_auth_ = host_->CreateChannelAuthenticator();
+  RunChannelAuth(false);
+
+  EXPECT_TRUE(client_socket_.get() != NULL);
+  EXPECT_TRUE(host_socket_.get() != NULL);
+
+  StreamConnectionTester tester(host_socket_.get(), client_socket_.get(),
+                                kMessageSize, kMessages);
+
+  tester.Start();
+  message_loop_.Run();
+  tester.CheckResults();
+}
+
+TEST_F(NegotiatingAuthenticatorTest, InvalidSecretHmac) {
+  ASSERT_NO_FATAL_FAILURE(InitAuthenticators(
+      kTestSharedSecret, kTestSharedSecretBad,
+      AuthenticationMethod::HMAC_SHA256, false));
+  ASSERT_NO_FATAL_FAILURE(RunAuthExchange());
+
+  VerifyRejected(Authenticator::INVALID_CREDENTIALS);
+}
+
+TEST_F(NegotiatingAuthenticatorTest, InvalidSecretPlain) {
+  ASSERT_NO_FATAL_FAILURE(InitAuthenticators(
+      kTestSharedSecret, kTestSharedSecretBad,
+      AuthenticationMethod::NONE, false));
+  ASSERT_NO_FATAL_FAILURE(RunAuthExchange());
+
+  VerifyRejected(Authenticator::INVALID_CREDENTIALS);
+}
+
+TEST_F(NegotiatingAuthenticatorTest, IncompatibleMethods) {
+  ASSERT_NO_FATAL_FAILURE(InitAuthenticators(
+      kTestSharedSecret, kTestSharedSecretBad,
+      AuthenticationMethod::NONE, true));
+  ASSERT_NO_FATAL_FAILURE(RunAuthExchange());
+
+  VerifyRejected(Authenticator::PROTOCOL_ERROR);
+}
+
+}  // namespace protocol
+}  // namespace remoting
diff --git a/remoting/protocol/v2_authenticator.cc b/remoting/protocol/v2_authenticator.cc
index 9e1184c..95b42d5 100644
--- a/remoting/protocol/v2_authenticator.cc
+++ b/remoting/protocol/v2_authenticator.cc
@@ -36,30 +36,32 @@ bool V2Authenticator::IsEkeMessage(const buzz::XmlElement* message) {
 
 // static
 scoped_ptr<Authenticator> V2Authenticator::CreateForClient(
-      const std::string& shared_secret) {
+    const std::string& shared_secret,
+    Authenticator::State initial_state) {
   return scoped_ptr<Authenticator>(new V2Authenticator(
-      P224EncryptedKeyExchange::kPeerTypeClient, shared_secret));
+      P224EncryptedKeyExchange::kPeerTypeClient, shared_secret, initial_state));
 }
 
 // static
 scoped_ptr<Authenticator> V2Authenticator::CreateForHost(
     const std::string& local_cert,
     const crypto::RSAPrivateKey& local_private_key,
-    const std::string& shared_secret) {
-  V2Authenticator* result = new V2Authenticator(
-      P224EncryptedKeyExchange::kPeerTypeServer, shared_secret);
+    const std::string& shared_secret,
+    Authenticator::State initial_state) {
+  scoped_ptr<V2Authenticator> result(new V2Authenticator(
+      P224EncryptedKeyExchange::kPeerTypeServer, shared_secret, initial_state));
   result->local_cert_ = local_cert;
   result->local_private_key_.reset(local_private_key.Copy());
-  result->state_ = WAITING_MESSAGE;
-  return scoped_ptr<Authenticator>(result);
+  return scoped_ptr<Authenticator>(result.Pass());
 }
 
 V2Authenticator::V2Authenticator(
     crypto::P224EncryptedKeyExchange::PeerType type,
-    const std::string& shared_secret)
+    const std::string& shared_secret,
+    Authenticator::State initial_state)
     : certificate_sent_(false),
       key_exchange_impl_(type, shared_secret),
-      state_(MESSAGE_READY),
+      state_(initial_state),
       rejection_reason_(INVALID_CREDENTIALS) {
   pending_messages_.push(key_exchange_impl_.GetMessage());
 }
@@ -168,6 +170,7 @@ scoped_ptr<buzz::XmlElement> V2Authenticator::GetNextMessage() {
     }
     certificate_tag->SetBodyText(base64_cert);
     message->AddElement(certificate_tag);
+    certificate_sent_ = true;
   }
 
   if (state_ != ACCEPTED) {
diff --git a/remoting/protocol/v2_authenticator.h b/remoting/protocol/v2_authenticator.h
index cd492b1..ef6503c 100644
--- a/remoting/protocol/v2_authenticator.h
+++ b/remoting/protocol/v2_authenticator.h
@@ -26,12 +26,14 @@ class V2Authenticator : public Authenticator {
   static bool IsEkeMessage(const buzz::XmlElement* message);
 
   static scoped_ptr<Authenticator> CreateForClient(
-      const std::string& shared_secret);
+      const std::string& shared_secret,
+      State initial_state);
 
   static scoped_ptr<Authenticator> CreateForHost(
       const std::string& local_cert,
       const crypto::RSAPrivateKey& local_private_key,
-      const std::string& shared_secret);
+      const std::string& shared_secret,
+      State initial_state);
 
   virtual ~V2Authenticator();
 
@@ -47,19 +49,20 @@ class V2Authenticator : public Authenticator {
   FRIEND_TEST_ALL_PREFIXES(V2AuthenticatorTest, InvalidSecret);
 
   V2Authenticator(crypto::P224EncryptedKeyExchange::PeerType type,
-                  const std::string& shared_secret);
+                  const std::string& shared_secret,
+                  State initial_state);
 
   bool is_host_side() const;
 
-  // Used only for HOST authenticators.
+  // Used only for host authenticators.
   std::string local_cert_;
   scoped_ptr<crypto::RSAPrivateKey> local_private_key_;
   bool certificate_sent_;
 
-  // Used only for CLIENT authenticators.
+  // Used only for client authenticators.
   std::string remote_cert_;
 
-  // Used for both HOST and CLIENT authenticators.
+  // Used for both host and client authenticators.
   crypto::P224EncryptedKeyExchange key_exchange_impl_;
   State state_;
   RejectionReason rejection_reason_;
diff --git a/remoting/protocol/v2_authenticator_unittest.cc b/remoting/protocol/v2_authenticator_unittest.cc
index fe2458e..0d634e4 100644
--- a/remoting/protocol/v2_authenticator_unittest.cc
+++ b/remoting/protocol/v2_authenticator_unittest.cc
@@ -41,8 +41,9 @@ class V2AuthenticatorTest : public AuthenticatorTestBase {
   void InitAuthenticators(const std::string& client_secret,
                           const std::string& host_secret) {
     host_ = V2Authenticator::CreateForHost(
-        host_cert_, *private_key_, host_secret);
-    client_ = V2Authenticator::CreateForClient(client_secret);
+        host_cert_, *private_key_, host_secret, Authenticator::WAITING_MESSAGE);
+    client_ = V2Authenticator::CreateForClient(
+        client_secret, Authenticator::MESSAGE_READY);
   }
 
   DISALLOW_COPY_AND_ASSIGN(V2AuthenticatorTest);
diff --git a/remoting/remoting.gyp b/remoting/remoting.gyp
index 3df81a2..996edab 100644
--- a/remoting/remoting.gyp
+++ b/remoting/remoting.gyp
@@ -795,6 +795,8 @@
         'protocol/message_decoder.h',
         'protocol/message_reader.cc',
         'protocol/message_reader.h',
+        'protocol/negotiating_authenticator.cc',
+        'protocol/negotiating_authenticator.h',
         'protocol/pepper_channel.h',
         'protocol/pepper_session.cc',
         'protocol/pepper_session.h',
@@ -955,6 +957,7 @@
         'protocol/key_event_tracker_unittest.cc',
         'protocol/message_decoder_unittest.cc',
         'protocol/message_reader_unittest.cc',
+        'protocol/negotiating_authenticator_unittest.cc',
         'protocol/pepper_session_unittest.cc',
         'protocol/protocol_mock_objects.cc',
         'protocol/protocol_mock_objects.h',