Encrypt/Decrypt/Validate SSU packet

SSU.cpp

@@ -1,5 +1,7 @@
+#include <string.h>
 #include <boost/bind.hpp>
 #include "Log.h"
+#include "RouterContext.h"
 #include "hmac.h"
 #include "SSU.h"
 
@@ -8,22 +10,94 @@ namespace i2p
 namespace ssu
 {
 
-	SSUSession::SSUSession (): m_State (eSessionStateUnknown)
+	SSUSession::SSUSession (SSUServer * server, const boost::asio::ip::udp::endpoint& remoteEndpoint,
+		i2p::data::RouterInfo * router): m_Server (server), m_RemoteEndpoint (remoteEndpoint), 
+		m_State (eSessionStateUnknown)
 	{
 	}
 
-	void SSUSession::ProcessNextMessage (uint8_t * buf, std::size_t len)
+	void SSUSession::ProcessNextMessage (uint8_t * buf, size_t len)
 	{
 		switch (m_State)
 		{
+			case eSessionStateUnknown:
+				// we assume session request
+				ProcessSessionRequest (buf, len);
+			break;
 			default:
 				LogPrint ("SSU state not implemented yet");
 		}
 	}
 
-	void SSUSession::Authenticate (uint8_t * buf, size_t len, uint8_t * aesKey, uint8_t * iv, uint8_t * macKey)
+	void SSUSession::ProcessSessionRequest (uint8_t * buf, size_t len)
+	{
+		auto address = i2p::context.GetRouterInfo ().GetSSUAddress ();
+		if (address)
+		{
+			// use intro key for verification and decryption
+			if (Validate (buf, len, address->key))
+			{
+				m_State = eSessionStateRequestReceived;
+				LogPrint ("Session request received");
+				Decrypt (buf, len, address->key);
+				// TODO:
+			}
+			else
+				LogPrint ("MAC verifcation failed");	
+		}
+		else
+			LogPrint ("SSU is not supported");
+	}
+
+	void SSUSession::Encrypt (uint8_t * buf, size_t len, uint8_t * aesKey, uint8_t * iv, uint8_t * macKey)
 	{	
+		if (len < sizeof (SSUHeader))
+		{
+			LogPrint ("Unexpected SSU packet length ", len);
+			return;
+		}
+		SSUHeader * header = (SSUHeader *)buf;
+		memcpy (header->iv, iv, 16);
+		uint8_t * encrypted = &header->flag;
+		uint16_t encryptedLen = len - (encrypted - buf);
 		m_Encryption.SetKeyWithIV (aesKey, 32, iv);
+		m_Encryption.ProcessData (encrypted, encrypted, encryptedLen);
+		// assume actual buffer size is 18 (16 + 2) bytes more
+		memcpy (buf + len, iv, 16);
+		*(uint16_t *)(buf + len + 16) = htobe16 (encryptedLen);
+		i2p::crypto::HMACMD5Digest (encrypted, encryptedLen + 18, macKey, header->mac);
+	}
+
+	void SSUSession::Decrypt (uint8_t * buf, size_t len, uint8_t * aesKey)
+	{
+		if (len < sizeof (SSUHeader))
+		{
+			LogPrint ("Unexpected SSU packet length ", len);
+			return;
+		}
+		SSUHeader * header = (SSUHeader *)buf;
+		uint8_t * encrypted = &header->flag;
+		uint16_t encryptedLen = len - (encrypted - buf);	
+		m_Decryption.SetKeyWithIV (aesKey, 32, header->iv);
+		m_Decryption.ProcessData (encrypted, encrypted, encryptedLen);
+	}
+
+	bool SSUSession::Validate (uint8_t * buf, size_t len, uint8_t * macKey)
+	{
+		if (len < sizeof (SSUHeader))
+		{
+			LogPrint ("Unexpected SSU packet length ", len);
+			return false;
+		}
+		SSUHeader * header = (SSUHeader *)buf;
+		uint8_t * encrypted = &header->flag;
+		uint16_t encryptedLen = len - (encrypted - buf);
+		// assume actual buffer size is 18 (16 + 2) bytes more
+		memcpy (buf + len, header->iv, 16);
+		*(uint16_t *)(buf + len + 16) = htobe16 (encryptedLen);
+		uint8_t digest[16];
+		i2p::crypto::HMACMD5Digest (encrypted, encryptedLen + 18, macKey, digest);
+		return !memcmp (header->mac, digest, 16);
 	}
 
 	SSUServer::SSUServer (boost::asio::io_service& service, int port):
@@ -47,6 +121,11 @@ namespace ssu
 		m_Socket.close ();
 	}
 
+	void SSUServer::Send (uint8_t * buf, size_t len, const boost::asio::ip::udp::endpoint& to)
+	{
+		m_Socket.send_to (boost::asio::buffer (buf, len), to);
+	}	
+
 	void SSUServer::Receive ()
 	{
 		m_Socket.async_receive_from (boost::asio::buffer (m_ReceiveBuffer, SSU_MTU), m_SenderEndpoint,
@@ -62,9 +141,9 @@ namespace ssu
 			auto it = m_Sessions.find (m_SenderEndpoint);
 			if (it != m_Sessions.end ())
 				session = it->second;
-			if (session)
+			if (!session)
 			{
-				session = new SSUSession ();
+				session = new SSUSession (this, m_SenderEndpoint);
 				m_Sessions[m_SenderEndpoint] = session;
 				LogPrint ("New SSU session from ", m_SenderEndpoint.address ().to_string (), ":", m_SenderEndpoint.port (), " created");
 			}
@@ -74,6 +153,33 @@ namespace ssu
 		else
 			LogPrint ("SSU receive error: ", ecode.message ());
 	}
+
+	SSUSession * SSUServer::GetSession (i2p::data::RouterInfo * router)
+	{
+		SSUSession * session = nullptr;
+		if (router)
+		{
+			auto address = router->GetSSUAddress ();
+			if (address)
+			{
+				boost::asio::ip::udp::endpoint remoteEndpoint (address->host, address->port);
+				auto it = m_Sessions.find (remoteEndpoint);
+				if (it != m_Sessions.end ())
+					session = it->second;
+				else
+				{
+					// otherwise create new session
+					session = new SSUSession (this, remoteEndpoint, router);
+					m_Sessions[remoteEndpoint] = session;
+					LogPrint ("New SSU session to [", router->GetIdentHashAbbreviation (), "] ",
+						remoteEndpoint.address ().to_string (), ":", remoteEndpoint.port (), " created");
+				}
+			}
+			else
+				LogPrint ("Router ", router->GetIdentHashAbbreviation (), " doesn't have SSU address");
+		}
+		return session;
+	}
 }
 }
 

SSU.h

@@ -7,6 +7,7 @@
 #include <cryptopp/modes.h>
 #include <cryptopp/aes.h>
 #include "I2PEndian.h"
+#include "RouterInfo.h"
 
 namespace i2p
 {
@@ -46,21 +47,30 @@ namespace ssu
 		eSessionStateEstablised
 	};		
 
+	class SSUServer;
 	class SSUSession
 	{
 		public:
 
-			SSUSession ();
-			void ProcessNextMessage (uint8_t * buf, size_t len);
-		
+			SSUSession (SSUServer * server, const boost::asio::ip::udp::endpoint& remoteEndpoint,
+				i2p::data::RouterInfo * router = nullptr);
+			void ProcessNextMessage (uint8_t * buf, size_t len);		
+
 		private:
 
-			void Authenticate (uint8_t * buf, size_t len, uint8_t * aesKey, uint8_t * iv, uint8_t * macKey);
+			void ProcessSessionRequest (uint8_t * buf, size_t len);
+
+			void Encrypt (uint8_t * buf, size_t len, uint8_t * aesKey, uint8_t * iv, uint8_t * macKey);
+			void Decrypt (uint8_t * buf, size_t len, uint8_t * aesKey);			
+			bool Validate (uint8_t * buf, size_t len, uint8_t * macKey);			
 
 		private:
 			
+			SSUServer * m_Server;
+			boost::asio::ip::udp::endpoint m_RemoteEndpoint;
 			SessionState m_State;	
-			CryptoPP::CBC_Mode<CryptoPP::AES>::Encryption m_Encryption;			
+			CryptoPP::CBC_Mode<CryptoPP::AES>::Encryption m_Encryption;	
+			CryptoPP::CBC_Mode<CryptoPP::AES>::Decryption m_Decryption;			
 	};
 
 	class SSUServer
@@ -71,6 +81,9 @@ namespace ssu
 			~SSUServer ();
 			void Start ();
 			void Stop ();
+			SSUSession * GetSession (i2p::data::RouterInfo * router);
+			
+			void Send (uint8_t * buf, size_t len, const boost::asio::ip::udp::endpoint& to);
 
 		private:
 
@@ -81,7 +94,7 @@ namespace ssu
 			
 			boost::asio::ip::udp::socket m_Socket;
 			boost::asio::ip::udp::endpoint m_SenderEndpoint;
-			uint8_t m_ReceiveBuffer[SSU_MTU];
+			uint8_t m_ReceiveBuffer[2*SSU_MTU];
 			std::map<boost::asio::ip::udp::endpoint, SSUSession *> m_Sessions;
 	};
 }