Allow to get key from SPAKE2 after the first round trip.

crypto/p224_spake.h

 // 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 CRYPTO_P224_SPAKE_H_
 #define CRYPTO_P224_SPAKE_H_
 
 #include <base/strings/string_piece.h>
 #include <crypto/p224.h>
 #include <crypto/sha2.h>
@@ skipping 50 matching lines @@
   // ProcessMessage processes a message which must have been generated by a
   // call to GetMessage() by the other party.
   Result ProcessMessage(const base::StringPiece& message);
 
   // In the event that ProcessMessage() returns kResultFailed, error will
   // return a human readable error message.
   const std::string& error() const;
 
   // The key established as result of the key exchange. Must be called
   // at then end after ProcessMessage() returns kResultSuccess.
-  const std::string& GetKey();
+  const std::string& GetKey() const;
+
+  // The key established as result of the key exchange. Can be called after
+  // the first ProcessMessage()
+  const std::string& GetUnverifiedKey() const;
 
  private:
   // The authentication state machine is very simple and each party proceeds
   // through each of these states, in order.
   enum State {
     kStateInitial,
     kStateRecvDH,
     kStateSendHash,
     kStateRecvHash,
     kStateDone,
@@ skipping 23 matching lines @@
   // expected_authenticator_ is used to store the hash value expected from the
   // other party.
   uint8 expected_authenticator_[kSHA256Length];
 
   std::string key_;
 };
 
 }  // namespace crypto
 
 #endif  // CRYPTO_P224_SPAKE_H_