remoting/protocol/pairing_authenticator_base.h

   1 // Copyright 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef REMOTING_PROTOCOL_PAIRING_AUTHENTICATOR_BASE_H_
   6 #define REMOTING_PROTOCOL_PAIRING_AUTHENTICATOR_BASE_H_
   7
   8 #include "base/memory/weak_ptr.h"
   9 #include "remoting/protocol/authenticator.h"
  10 #include "third_party/libjingle/source/talk/xmllite/xmlelement.h"
  11
  12 namespace remoting {
  13 namespace protocol {
  14
  15 // The pairing authenticator builds on top of V2Authenticator to add
  16 // support for PIN-less authentication via device pairing:
  17 //
  18 // * If a client device is already paired, it includes in the initial
  19 //   authentication message a Client Id and the first SPAKE message
  20 //   using the Paired Secret and HMAC_SHA256.
  21 // * If the host recognizes the Client Id, it looks up the corresponding
  22 //   Paired Secret and continue the SPAKE exchange.
  23 // * If it does not recognize the Client Id, it initiates a SPAKE exchange
  24 //   with HMAC_SHA256 using the PIN as the shared secret. The initial
  25 //   message of this exchange includes an an error message, which
  26 //   informs the client that the PIN-less connection failed and causes
  27 //   it to prompt the user for a PIN to use for authentication
  28 //   instead.
  29 // * If, at any point, the SPAKE exchange fails with the Paired Secret,
  30 //   the endpoint that detects the failure initiates a new SPAKE exchange
  31 //   using the PIN, and includes an error message to instruct the peer
  32 //   to do likewise.
  33 //
  34 // If a client device is not already paired, but supports pairing, then
  35 // the V2Authenticator is used instead of this class. Only the method name
  36 // differs, which the client uses to determine that pairing should be offered
  37 // to the user (see NegotiatingHostAuthenticator::CreateAuthenticator and
  38 // NegotiatingClientAuthenticator::CreateAuthenticatorForCurrentMethod).
  39 class PairingAuthenticatorBase : public Authenticator {
  40  public:
  41   PairingAuthenticatorBase();
  42   virtual ~PairingAuthenticatorBase();
  43
  44   // Authenticator interface.
  45   virtual State state() const OVERRIDE;
  46   virtual RejectionReason rejection_reason() const OVERRIDE;
  47   virtual void ProcessMessage(const buzz::XmlElement* message,
  48                               const base::Closure& resume_callback) OVERRIDE;
  49   virtual scoped_ptr<buzz::XmlElement> GetNextMessage() OVERRIDE;
  50   virtual scoped_ptr<ChannelAuthenticator>
  51       CreateChannelAuthenticator() const OVERRIDE;
  52
  53  protected:
  54   typedef base::Callback<void(scoped_ptr<Authenticator> authenticator)>
  55       SetAuthenticatorCallback;
  56
  57   static const buzz::StaticQName kPairingInfoTag;
  58   static const buzz::StaticQName kClientIdAttribute;
  59
  60   // Create a V2 authenticator in the specified state, prompting the user for
  61   // the PIN first if necessary.
  62   virtual void CreateV2AuthenticatorWithPIN(
  63       State initial_state,
  64       const SetAuthenticatorCallback& callback) = 0;
  65
  66   // Amend an authenticator message, for example to add client- or host-specific
  67   // elements to it.
  68   virtual void AddPairingElements(buzz::XmlElement* message) = 0;
  69
  70   // A non-fatal error message that derived classes should set in order to
  71   // cause the peer to be notified that pairing has failed and that it should
  72   // fall back on PIN authentication. This string need not be human-readable,
  73   // nor is it currently used other than being logged.
  74   std::string error_message_;
  75
  76   // The underlying V2 authenticator, created with either the PIN or the
  77   // Paired Secret by the derived class.
  78   scoped_ptr<Authenticator> v2_authenticator_;
  79
  80   // Derived classes must set this to True if the underlying authenticator is
  81   // using the Paired Secret.
  82   bool using_paired_secret_;
  83
  84  private:
  85   // Helper methods for ProcessMessage and GetNextMessage
  86   void MaybeAddErrorMessage(buzz::XmlElement* message);
  87   bool HasErrorMessage(const buzz::XmlElement* message) const;
  88   void CheckForFailedSpakeExchange(const base::Closure& resume_callback);
  89   void SetAuthenticatorAndProcessMessage(
  90       const buzz::XmlElement* message,
  91       const base::Closure& resume_callback,
  92       scoped_ptr<Authenticator> authenticator);
  93
  94   // Set to true if a PIN-based authenticator has been requested but has not
  95   // yet been set.
  96   bool waiting_for_authenticator_;
  97
  98   base::WeakPtrFactory<PairingAuthenticatorBase> weak_factory_;
  99
 100   DISALLOW_COPY_AND_ASSIGN(PairingAuthenticatorBase);
 101 };
 102
 103 }  // namespace protocol
 104 }  // namespace remoting
 105
 106 #endif  // REMOTING_PROTOCOL_PAIRING_AUTHENTICATOR_H_