calculate shared key in separate therad

NTCPSession.cpp

@@ -1,5 +1,6 @@
 #include <string.h>
 #include <stdlib.h>
+#include <future>
 
 #include "I2PEndian.h"
 #include "Base.h"
@@ -38,7 +39,7 @@ namespace transport
 	void NTCPSession::CreateAESKey (uint8_t * pubKey, i2p::crypto::AESKey& key)
 	{
 		uint8_t sharedKey[256];
-		m_DHKeysPair->Agree (pubKey, sharedKey);
+		m_DHKeysPair->Agree (pubKey, sharedKey); // time consuming operation
 		
 		uint8_t * aesKey = key;
 		if (sharedKey[0] & 0x80)
@@ -228,9 +229,26 @@ namespace transport
 			}
 		}
 		else
+		{	
+			auto s = shared_from_this ();
+			// create AES key in separate thread
+			auto createKey = std::async (std::launch::async, [s] ()->i2p::crypto::AESKey
 				{
 					i2p::crypto::AESKey aesKey;
-			CreateAESKey (m_Establisher->phase2.pubKey, aesKey);
+					s->CreateAESKey (s->m_Establisher->phase2.pubKey, aesKey);
+					return std::move (aesKey);
+				}).share (); // TODO: use move capture in C++ 14 instead shared_future							 
+			// let other operations execute while a key gets created
+			m_Server.GetService ().post ([s, createKey]()
+				{  
+					auto aesKey = createKey.get (); // we might wait if no more pending operations
+					s->HandlePhase2 (aesKey);
+				});	
+		}	
+	}	
+
+	void NTCPSession::HandlePhase2 (const i2p::crypto::AESKey& aesKey)
+	{
 		m_Decryption.SetKey (aesKey);
 		m_Decryption.SetIV (m_Establisher->phase2.pubKey + 240);
 		m_Encryption.SetKey (aesKey);
@@ -253,7 +271,6 @@ namespace transport
 		}	
 		SendPhase3 ();
 	}				
-	}	
 		
 	void NTCPSession::SendPhase3 ()
 	{

NTCPSession.h

@@ -73,6 +73,7 @@ namespace transport
 			void SendPhase3 ();
 			void HandlePhase1Sent (const boost::system::error_code& ecode,  std::size_t bytes_transferred);
 			void HandlePhase2Received (const boost::system::error_code& ecode, std::size_t bytes_transferred);
+			void HandlePhase2 (const i2p::crypto::AESKey& aesKey);
 			void HandlePhase3Sent (const boost::system::error_code& ecode, std::size_t bytes_transferred, uint32_t tsA);
 			void HandlePhase4Received (const boost::system::error_code& ecode, std::size_t bytes_transferred, uint32_t tsA);