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      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_
    107