PairingAuthenticator implementation and plumbing.

remoting/protocol/pairing_authenticator_base.h

+// 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.
+
+#ifndef REMOTING_PROTOCOL_PAIRING_AUTHENTICATOR_BASE_H_
+#define REMOTING_PROTOCOL_PAIRING_AUTHENTICATOR_BASE_H_
+
+#include "base/memory/weak_ptr.h"
+#include "remoting/protocol/authenticator.h"
+#include "third_party/libjingle/source/talk/xmllite/xmlelement.h"
+
+namespace remoting {
+namespace protocol {
+
+// The pairing authenticator builds on top of V2Authenticator to add
+// support for PIN-less authentication via device pairing:
+//
+// * If a client device is already paired, it includes in the initial
+//   authentication message a Client Id and the first SPAKE message
+//   using the Paired Secret and HMAC_SHA256.
+// * If the host recognizes the Client Id, it looks up the corresponding
+//   Paired Secret and continue the SPAKE exchange.
+// * If it does not recognize the Client Id, it initiates a SPAKE exchange
+//   with HMAC_SHA256 using the PIN as the shared secret. The initial
+//   message of this exchange includes an an error message, which
+//   informs the client that the PIN-less connection failed and causes
+//   it to prompt the user for a PIN to use for authentication
+//   instead.
+// * If, at any point, the SPAKE exchange fails with the Paired Secret,
+//   the endpoint that detects the failure initiates a new SPAKE exchange
+//   using the PIN, and includes an error message to instruct the peer
+//   to do likewise.
+//
+// If a client device is not already paired, but supports pairing, then
+// the V2Authenticator is used instead of this class. Only the method name
+// differs, which the client uses to determine that pairing should be offered
+// to the user (see NegotiatingHostAuthenticator::CreateAuthenticator and
+// NegotiatingClientAuthenticator::CreateAuthenticatorForCurrentMethod).
+class PairingAuthenticatorBase : public Authenticator {
+ public:
+  PairingAuthenticatorBase();
+  virtual ~PairingAuthenticatorBase();
+
+  // Authenticator interface.
+  virtual State state() const OVERRIDE;
+  virtual RejectionReason rejection_reason() const OVERRIDE;
+  virtual void ProcessMessage(const buzz::XmlElement* message,
+                              const base::Closure& resume_callback) OVERRIDE;
+  virtual scoped_ptr<buzz::XmlElement> GetNextMessage() OVERRIDE;
+  virtual scoped_ptr<ChannelAuthenticator>
+      CreateChannelAuthenticator() const OVERRIDE;
+
+ protected:
+  typedef base::Callback<void(scoped_ptr<Authenticator> authenticator)>
+      SetAuthenticatorCallback;
+
+  static const buzz::StaticQName kPairingInfoTag;
+  static const buzz::StaticQName kClientIdAttribute;
+
+  // Create a V2 authenticator in the specified state, prompting the user for
+  // the PIN first if necessary.
+  virtual void CreateV2AuthenticatorWithPIN(
+      State initial_state,
+      const SetAuthenticatorCallback& callback) = 0;
+
+  // Amend an authenticator message, for example to add client- or host-specific
+  // elements to it.
+  virtual void AddPairingElements(buzz::XmlElement* message) = 0;
+
+  // A non-fatal error message that derived classes should set in order to
+  // cause the peer to be notified that pairing has failed and that it should
+  // fall back on PIN authentication. This string need not be human-readable,
+  // nor is it currently used other than being logged.
+  std::string error_message_;
+
+  // The underlying V2 authenticator, created with either the PIN or the
+  // Paired Secret by the derived class.
+  scoped_ptr<Authenticator> v2_authenticator_;
+
+  // Derived classes must set this to True if the underlying authenticator is
+  // using the Paired Secret.
+  bool using_paired_secret_;
+
+ private:
+  // Helper methods for ProcessMessage and GetNextMessage
+  void MaybeAddErrorMessage(buzz::XmlElement* message);
+  bool HasErrorMessage(const buzz::XmlElement* message) const;
+  void CheckForFailedSpakeExchange(const base::Closure& resume_callback);
+  void SetAuthenticatorAndProcessMessage(
+      const buzz::XmlElement* message,
+      const base::Closure& resume_callback,
+      scoped_ptr<Authenticator> authenticator);
+
+  // Set to true if a PIN-based authenticator has been requested but has not
+  // yet been set.
+  bool waiting_for_authenticator_;
+
+  base::WeakPtrFactory<PairingAuthenticatorBase> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(PairingAuthenticatorBase);
+};
+
+}  // namespace protocol
+}  // namespace remoting
+
+#endif  // REMOTING_PROTOCOL_PAIRING_AUTHENTICATOR_H_