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

crypto/p224_spake.cc

 // 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.
 
 // This code implements SPAKE2, a variant of EKE:
 //  http://www.di.ens.fr/~pointche/pub.php?reference=AbPo04
 
 #include <crypto/p224_spake.h>
 
 #include <base/logging.h>
@@ skipping 222 matching lines @@
       std::string(reinterpret_cast<const char *>(pw_), sizeof(pw_));
   hash_contents += k;
 
   SHA256HashString(hash_contents, out_digest, kSHA256Length);
 }
 
 const std::string& P224EncryptedKeyExchange::error() const {
   return error_;
 }
 
-const std::string& P224EncryptedKeyExchange::GetKey() {
+const std::string& P224EncryptedKeyExchange::GetKey() const {
   DCHECK_EQ(state_, kStateDone);
+  return GetUnverifiedKey();
+}
+
+const std::string& P224EncryptedKeyExchange::GetUnverifiedKey() const {
+  // Key is already final when state is kStateSendHash. Subsequent states are
+  // used only for verification of the key. Some users may combine verification
+  // with sending verifiable data instead of |expected_authenticator_|.
+  DCHECK_GE(state_, kStateSendHash);
   return key_;
 }
 
 }  // namespace crypto