i2pd/core/transport/SSUSession.cpp

#include <boost/bind.hpp>
#include <cryptopp/dh.h>
#include <cryptopp/sha.h>
#include "crypto/CryptoConst.h"
#include "util/Log.h"
#include "util/Timestamp.h"
#include "RouterContext.h"
#include "Transports.h"
#include "SSU.h"
#include "SSUSession.h"

namespace i2p
{
namespace transport
{
    SSUSession::SSUSession (SSUServer& server, boost::asio::ip::udp::endpoint& remoteEndpoint,
        std::shared_ptr<const i2p::data::RouterInfo> router, bool peerTest ): TransportSession (router), 
        m_Server (server), m_RemoteEndpoint (remoteEndpoint), m_Timer (GetService ()), 
        m_PeerTest (peerTest),m_State (eSessionStateUnknown), m_IsSessionKey (false), 
        m_RelayTag (0),m_Data (*this), m_IsDataReceived (false)
    {
        m_CreationTime = i2p::util::GetSecondsSinceEpoch ();
    }

    SSUSession::~SSUSession ()
    {       
    }   

    boost::asio::io_service& SSUSession::GetService () 
    { 
        return IsV6 () ? m_Server.GetServiceV6 () : m_Server.GetService (); 
    }
    
    void SSUSession::CreateAESandMacKey (const uint8_t * pubKey)
    {
        CryptoPP::DH dh (i2p::crypto::elgp, i2p::crypto::elgg);
        uint8_t sharedKey[256];
        if (!dh.Agree (sharedKey, m_DHKeysPair->privateKey, pubKey))
        {    
            LogPrint (eLogError, "Couldn't create shared key");
            return;
        };

        uint8_t * sessionKey = m_SessionKey, * macKey = m_MacKey;
        if (sharedKey[0] & 0x80)
        {
            sessionKey[0] = 0;
            memcpy (sessionKey + 1, sharedKey, 31);
            memcpy (macKey, sharedKey + 31, 32);
        }   
        else if (sharedKey[0])
        {
            memcpy (sessionKey, sharedKey, 32);
            memcpy (macKey, sharedKey + 32, 32);
        }   
        else
        {   
            // find first non-zero byte
            uint8_t * nonZero = sharedKey + 1;
            while (!*nonZero)
            {
                nonZero++;
                if (nonZero - sharedKey > 32)
                {
                    LogPrint ("First 32 bytes of shared key is all zeros. Ignored");
                    return;
                }   
            }
            
            memcpy (sessionKey, nonZero, 32);
            CryptoPP::SHA256().CalculateDigest(macKey, nonZero, 64 - (nonZero - sharedKey));
        }
        m_IsSessionKey = true;
        m_SessionKeyEncryption.SetKey (m_SessionKey);
        m_SessionKeyDecryption.SetKey (m_SessionKey);
    }       

    void SSUSession::ProcessNextMessage (uint8_t * buf, size_t len, const boost::asio::ip::udp::endpoint& senderEndpoint)
    {
        m_NumReceivedBytes += len;
        i2p::transport::transports.UpdateReceivedBytes (len);
        if (m_State == eSessionStateIntroduced)
        {
            // HolePunch received
            LogPrint ("SSU HolePunch of ", len, " bytes received");
            m_State = eSessionStateUnknown;
            Connect ();
        }
        else
        {
            if (!len) return; // ignore zero-length packets 
            if (m_State == eSessionStateEstablished)
                ScheduleTermination ();     
            
            if (m_IsSessionKey && Validate (buf, len, m_MacKey)) // try session key first
                DecryptSessionKey (buf, len);   
            else 
            {
                // try intro key depending on side
                auto introKey = GetIntroKey ();
                if (introKey && Validate (buf, len, introKey))
                    Decrypt (buf, len, introKey);
                else
                {    
                    // try own intro key
                    auto address = i2p::context.GetRouterInfo ().GetSSUAddress ();
                    if (!address)
                    {
                        LogPrint (eLogError, "SSU is not supported");
                        return;
                    }   
                    if (Validate (buf, len, address->key))
                        Decrypt (buf, len, address->key);
                    else
                    {
                        LogPrint (eLogError, "MAC verification failed ", len, " bytes from ", senderEndpoint);
                        m_Server.DeleteSession (shared_from_this ()); 
                        return;
                    }   
                }   
            }   
            // successfully decrypted
            ProcessMessage (buf, len, senderEndpoint);
        }   
    }

    void SSUSession::ProcessMessage (uint8_t * buf, size_t len, const boost::asio::ip::udp::endpoint& senderEndpoint)
    {
        len -= (len & 0x0F); // %16, delete extra padding
        if (len <= sizeof (SSUHeader)) return; // drop empty message
        //TODO: since we are accessing a uint8_t this is unlikely to crash due to alignment but should be improved
        SSUHeader * header = (SSUHeader *)buf;
        switch (header->GetPayloadType ())
        {
            case PAYLOAD_TYPE_DATA:
                ProcessData (buf + sizeof (SSUHeader), len - sizeof (SSUHeader));
            break;
            case PAYLOAD_TYPE_SESSION_REQUEST:
                ProcessSessionRequest (buf, len, senderEndpoint);               
            break;
            case PAYLOAD_TYPE_SESSION_CREATED:
                ProcessSessionCreated (buf, len);
            break;
            case PAYLOAD_TYPE_SESSION_CONFIRMED:
                ProcessSessionConfirmed (buf, len);
            break;  
            case PAYLOAD_TYPE_PEER_TEST:
                LogPrint (eLogDebug, "SSU peer test received");
                ProcessPeerTest (buf + sizeof (SSUHeader), len - sizeof (SSUHeader), senderEndpoint);
            break;
            case PAYLOAD_TYPE_SESSION_DESTROYED:
            {
                LogPrint (eLogDebug, "SSU session destroy received");
                m_Server.DeleteSession (shared_from_this ()); 
                break;
            }   
            case PAYLOAD_TYPE_RELAY_RESPONSE:
                ProcessRelayResponse (buf, len);
                if (m_State != eSessionStateEstablished)
                    m_Server.DeleteSession (shared_from_this ());
            break;
            case PAYLOAD_TYPE_RELAY_REQUEST:
                LogPrint (eLogDebug, "SSU relay request received");
                ProcessRelayRequest (buf + sizeof (SSUHeader), len - sizeof (SSUHeader), senderEndpoint);
            break;
            case PAYLOAD_TYPE_RELAY_INTRO:
                LogPrint (eLogDebug, "SSU relay intro received");
                ProcessRelayIntro (buf + sizeof (SSUHeader), len - sizeof (SSUHeader));
            break;
            default:
                LogPrint (eLogWarning, "Unexpected SSU payload type ", (int)header->GetPayloadType ());
        }
    }

    void SSUSession::ProcessSessionRequest (uint8_t * buf, size_t len, const boost::asio::ip::udp::endpoint& senderEndpoint)
    {
        LogPrint (eLogDebug, "Session request received");   
        m_RemoteEndpoint = senderEndpoint;
        if (!m_DHKeysPair)
            m_DHKeysPair = transports.GetNextDHKeysPair ();
        CreateAESandMacKey (buf + sizeof (SSUHeader));
        SendSessionCreated (buf + sizeof (SSUHeader));
    }

    void SSUSession::ProcessSessionCreated (uint8_t * buf, size_t len)
    {
        if (!m_RemoteRouter || !m_DHKeysPair)
        {
            LogPrint (eLogWarning, "Unsolicited session created message");
            return;
        }

        LogPrint (eLogDebug, "Session created received");   
        m_Timer.cancel (); // connect timer
        SignedData s; // x,y, our IP, our port, remote IP, remote port, relayTag, signed on time 
        uint8_t * payload = buf + sizeof (SSUHeader);   
        uint8_t * y = payload;
        CreateAESandMacKey (y);
        s.Insert (m_DHKeysPair->publicKey, 256); // x
        s.Insert (y, 256); // y
        payload += 256;
        uint8_t addressSize = *payload;
        payload += 1; // size
        uint8_t * ourAddress = payload;
        boost::asio::ip::address ourIP;
        if (addressSize == 4) // v4
        {   
            boost::asio::ip::address_v4::bytes_type bytes;
            memcpy (bytes.data (), ourAddress, 4);
            ourIP = boost::asio::ip::address_v4 (bytes);
        }   
        else // v6
        {
            boost::asio::ip::address_v6::bytes_type bytes;
            memcpy (bytes.data (), ourAddress, 16);
            ourIP = boost::asio::ip::address_v6 (bytes);
        }   
        s.Insert (ourAddress, addressSize); // our IP 
        payload += addressSize; // address
        uint16_t ourPort = bufbe16toh (payload);
        s.Insert (payload, 2); // our port
        payload += 2; // port
        LogPrint ("Our external address is ", ourIP.to_string (), ":", ourPort);
        i2p::context.UpdateAddress (ourIP);
        if (m_RemoteEndpoint.address ().is_v4 ())
            s.Insert (m_RemoteEndpoint.address ().to_v4 ().to_bytes ().data (), 4); // remote IP v4
        else
            s.Insert (m_RemoteEndpoint.address ().to_v6 ().to_bytes ().data (), 16); // remote IP v6
        s.Insert<uint16_t> (htobe16 (m_RemoteEndpoint.port ())); // remote port
        s.Insert (payload, 8); // relayTag and signed on time 
        m_RelayTag = bufbe32toh (payload);
        payload += 4; // relayTag
        payload += 4; // signed on time
        // decrypt signature
        size_t signatureLen = m_RemoteIdentity.GetSignatureLen ();
        size_t paddingSize = signatureLen & 0x0F; // %16
        if (paddingSize > 0) signatureLen += (16 - paddingSize);
        //TODO: since we are accessing a uint8_t this is unlikely to crash due to alignment but should be improved
        m_SessionKeyDecryption.SetIV (((SSUHeader *)buf)->iv);
        m_SessionKeyDecryption.Decrypt (payload, signatureLen, payload);
        // verify
        if (!s.Verify (m_RemoteIdentity, payload))
            LogPrint (eLogError, "SSU signature verification failed");
        m_RemoteIdentity.DropVerifier ();   
        
        SendSessionConfirmed (y, ourAddress, addressSize + 2);
    }   

    void SSUSession::ProcessSessionConfirmed (uint8_t * buf, size_t len)
    {
        LogPrint (eLogDebug, "Session confirmed received"); 
        uint8_t * payload = buf + sizeof (SSUHeader);
        payload++; // identity fragment info
        uint16_t identitySize = bufbe16toh (payload);   
        payload += 2; // size of identity fragment
        m_RemoteIdentity.FromBuffer (payload, identitySize);
        m_Data.UpdatePacketSize (m_RemoteIdentity.GetIdentHash ());
        payload += identitySize; // identity    
        payload += 4; // signed-on time
        size_t paddingSize = (payload - buf) + m_RemoteIdentity.GetSignatureLen ();
        paddingSize &= 0x0F;  // %16
        if (paddingSize > 0) paddingSize = 16 - paddingSize;
        payload += paddingSize;
        // TODO: verify signature (need data from session request), payload points to signature
        m_Data.Send (CreateDeliveryStatusMsg (0));
        Established ();
    }

    void SSUSession::SendSessionRequest ()
    {
        auto introKey = GetIntroKey ();
        if (!introKey)
        {
            LogPrint (eLogError, "SSU is not supported");
            return;
        }
    
        uint8_t buf[320 + 18] = {}; // 304 bytes for ipv4, 320 for ipv6, all set to 0
        uint8_t * payload = buf + sizeof (SSUHeader);
        memcpy (payload, m_DHKeysPair->publicKey, 256); // x
        bool isV4 = m_RemoteEndpoint.address ().is_v4 ();
        if (isV4)
        {
            payload[256] = 4; 
            memcpy (payload + 257, m_RemoteEndpoint.address ().to_v4 ().to_bytes ().data(), 4); 
        }
        else
        {
            payload[256] = 16; 
            memcpy (payload + 257, m_RemoteEndpoint.address ().to_v6 ().to_bytes ().data(), 16); 
        }   
        
        uint8_t iv[16];
        CryptoPP::RandomNumberGenerator& rnd = i2p::context.GetRandomNumberGenerator ();
        rnd.GenerateBlock (iv, 16); // random iv
        FillHeaderAndEncrypt (PAYLOAD_TYPE_SESSION_REQUEST, buf, isV4 ? 304 : 320, introKey, iv, introKey);
        m_Server.Send (buf, isV4 ? 304 : 320, m_RemoteEndpoint);
    }

    void SSUSession::SendRelayRequest (uint32_t iTag, const uint8_t * iKey)
    {
        auto address = i2p::context.GetRouterInfo ().GetSSUAddress ();
        if (!address)
        {
            LogPrint (eLogError, "SSU is not supported");
            return;
        }
    
        uint8_t buf[96 + 18] = {}; 
        uint8_t * payload = buf + sizeof (SSUHeader);
        htobe32buf (payload, iTag);
        payload += 4;
        *payload = 0; // no address
        payload++;
        htobuf16(payload, 0); // port = 0
        payload += 2;
        *payload = 0; // challenge
        payload++;  
        memcpy (payload, (const uint8_t *)address->key, 32);
        payload += 32;
        CryptoPP::RandomNumberGenerator& rnd = i2p::context.GetRandomNumberGenerator ();
        htobe32buf (payload, rnd.GenerateWord32 ()); // nonce   

        uint8_t iv[16];
        rnd.GenerateBlock (iv, 16); // random iv
        if (m_State == eSessionStateEstablished)
            FillHeaderAndEncrypt (PAYLOAD_TYPE_RELAY_REQUEST, buf, 96, m_SessionKey, iv, m_MacKey);
        else
            FillHeaderAndEncrypt (PAYLOAD_TYPE_RELAY_REQUEST, buf, 96, iKey, iv, iKey);         
        m_Server.Send (buf, 96, m_RemoteEndpoint);
    }

    void SSUSession::SendSessionCreated (const uint8_t * x)
    {
        auto introKey = GetIntroKey ();
        auto address = IsV6 () ? i2p::context.GetRouterInfo ().GetSSUV6Address () :
            i2p::context.GetRouterInfo ().GetSSUAddress (true); //v4 only
        if (!introKey || !address)
        {
            LogPrint (eLogError, "SSU is not supported");
            return;
        }
        CryptoPP::RandomNumberGenerator& rnd = i2p::context.GetRandomNumberGenerator ();
        SignedData s; // x,y, remote IP, remote port, our IP, our port, relayTag, signed on time 
        s.Insert (x, 256); // x

        uint8_t buf[384 + 18] = {};
        uint8_t * payload = buf + sizeof (SSUHeader);
        memcpy (payload, m_DHKeysPair->publicKey, 256);
        s.Insert (payload, 256); // y
        payload += 256;
        if (m_RemoteEndpoint.address ().is_v4 ())
        {
            // ipv4
            *payload = 4;
            payload++;
            memcpy (payload, m_RemoteEndpoint.address ().to_v4 ().to_bytes ().data(), 4); 
            s.Insert (payload, 4); // remote endpoint IP V4
            payload += 4;
        }
        else
        {
            // ipv6
            *payload = 16;
            payload++;
            memcpy (payload, m_RemoteEndpoint.address ().to_v6 ().to_bytes ().data(), 16); 
            s.Insert (payload, 16); // remote endpoint IP V6
            payload += 16;
        }
        htobe16buf (payload, m_RemoteEndpoint.port ());
        s.Insert (payload, 2); // remote port
        payload += 2;
        if (address->host.is_v4 ())
            s.Insert (address->host.to_v4 ().to_bytes ().data (), 4); // our IP V4
        else
            s.Insert (address->host.to_v6 ().to_bytes ().data (), 16); // our IP V6
        s.Insert<uint16_t> (htobe16 (address->port)); // our port
        uint32_t relayTag = 0;
        if (i2p::context.GetRouterInfo ().IsIntroducer ())
        {
            relayTag = rnd.GenerateWord32 ();
            if (!relayTag) relayTag = 1;
            m_Server.AddRelay (relayTag, m_RemoteEndpoint);
        }
        htobe32buf (payload, relayTag); 
        payload += 4; // relay tag 
        htobe32buf (payload, i2p::util::GetSecondsSinceEpoch ()); // signed on time
        payload += 4;
        s.Insert (payload - 8, 8); // relayTag and signed on time 
        s.Sign (i2p::context.GetPrivateKeys (), payload); // DSA signature
        // TODO: fill padding with random data  

        uint8_t iv[16];
        rnd.GenerateBlock (iv, 16); // random iv
        // encrypt signature and padding with newly created session key 
        size_t signatureLen = i2p::context.GetIdentity ().GetSignatureLen ();
        size_t paddingSize = signatureLen & 0x0F; // %16
        if (paddingSize > 0) signatureLen += (16 - paddingSize);
        m_SessionKeyEncryption.SetIV (iv);
        m_SessionKeyEncryption.Encrypt (payload, signatureLen, payload);
        payload += signatureLen;
        size_t msgLen = payload - buf;
        
        // encrypt message with intro key
        FillHeaderAndEncrypt (PAYLOAD_TYPE_SESSION_CREATED, buf, msgLen, introKey, iv, introKey);   
        Send (buf, msgLen);
    }

    void SSUSession::SendSessionConfirmed (const uint8_t * y, const uint8_t * ourAddress, size_t ourAddressLen)
    {
        uint8_t buf[512 + 18] = {};
        uint8_t * payload = buf + sizeof (SSUHeader);
        *payload = 1; // 1 fragment
        payload++; // info
        size_t identLen = i2p::context.GetIdentity ().GetFullLen (); // 387+ bytes
        htobe16buf (payload, identLen);
        payload += 2; // cursize
        i2p::context.GetIdentity ().ToBuffer (payload, identLen);
        payload += identLen;
        uint32_t signedOnTime = i2p::util::GetSecondsSinceEpoch ();
        htobe32buf (payload, signedOnTime); // signed on time
        payload += 4;
        auto signatureLen = i2p::context.GetIdentity ().GetSignatureLen ();
        size_t paddingSize = ((payload - buf) + signatureLen)%16;
        if (paddingSize > 0) paddingSize = 16 - paddingSize;
        // TODO: fill padding   
        payload += paddingSize; // padding size

        // signature        
        SignedData s; // x,y, our IP, our port, remote IP, remote port, relayTag, our signed on time 
        s.Insert (m_DHKeysPair->publicKey, 256); // x
        s.Insert (y, 256); // y
        s.Insert (ourAddress, ourAddressLen); // our address/port as seem by party
        if (m_RemoteEndpoint.address ().is_v4 ())
            s.Insert (m_RemoteEndpoint.address ().to_v4 ().to_bytes ().data (), 4); // remote IP V4
        else
            s.Insert (m_RemoteEndpoint.address ().to_v6 ().to_bytes ().data (), 16); // remote IP V6    
        s.Insert<uint16_t> (htobe16 (m_RemoteEndpoint.port ())); // remote port
        s.Insert (htobe32 (m_RelayTag)); // relay tag
        s.Insert (htobe32 (signedOnTime)); // signed on time
        s.Sign (i2p::context.GetPrivateKeys (), payload); // DSA signature  
        payload += signatureLen;
        
        size_t msgLen = payload - buf;
        uint8_t iv[16];
        CryptoPP::RandomNumberGenerator& rnd = i2p::context.GetRandomNumberGenerator ();
        rnd.GenerateBlock (iv, 16); // random iv
        // encrypt message with session key
        FillHeaderAndEncrypt (PAYLOAD_TYPE_SESSION_CONFIRMED, buf, msgLen, m_SessionKey, iv, m_MacKey);
        Send (buf, msgLen);
    }

    void SSUSession::ProcessRelayRequest (uint8_t * buf, size_t len, const boost::asio::ip::udp::endpoint& from)
    {
        uint32_t relayTag = bufbe32toh (buf);
        auto session = m_Server.FindRelaySession (relayTag);
        if (session)
        {
            buf += 4; // relay tag  
            uint8_t size = *buf;
            buf++; // size
            buf += size; // address
            buf += 2; // port
            uint8_t challengeSize = *buf;
            buf++; // challenge size
            buf += challengeSize;
            uint8_t * introKey = buf;
            buf += 32; // introkey
            uint32_t nonce = bufbe32toh (buf);
            SendRelayResponse (nonce, from, introKey, session->m_RemoteEndpoint);
            SendRelayIntro (session.get (), from);
        }   
    }

    void SSUSession::SendRelayResponse (uint32_t nonce, const boost::asio::ip::udp::endpoint& from,
        const uint8_t * introKey, const boost::asio::ip::udp::endpoint& to)
    {
        uint8_t buf[80 + 18] = {}; // 64 Alice's ipv4 and 80 Alice's ipv6
        uint8_t * payload = buf + sizeof (SSUHeader);
        // Charlie's address always v4
        if (!to.address ().is_v4 ())
        {
            LogPrint (eLogError, "Charlie's IP must be v4");
            return;
        }
        *payload = 4;
        payload++; // size
        htobe32buf (payload, to.address ().to_v4 ().to_ulong ()); // Charlie's IP
        payload += 4; // address    
        htobe16buf (payload, to.port ()); // Charlie's port
        payload += 2; // port
        // Alice
        bool isV4 = from.address ().is_v4 (); // Alice's
        if (isV4)
        {
            *payload = 4;
            payload++; // size
            memcpy (payload, from.address ().to_v4 ().to_bytes ().data (), 4); // Alice's IP V4
            payload += 4; // address    
        }
        else
        {
            *payload = 16;
            payload++; // size
            memcpy (payload, from.address ().to_v6 ().to_bytes ().data (), 16); // Alice's IP V6
            payload += 16; // address   
        }
        htobe16buf (payload, from.port ()); // Alice's port
        payload += 2; // port
        htobe32buf (payload, nonce);        

        if (m_State == eSessionStateEstablished)
        {   
            // encrypt with session key
            FillHeaderAndEncrypt (PAYLOAD_TYPE_RELAY_RESPONSE, buf, isV4 ? 64 : 80);
            Send (buf, isV4 ? 64 : 80);
        }   
        else
        {
            // ecrypt with Alice's intro key
            uint8_t iv[16];
            CryptoPP::RandomNumberGenerator& rnd = i2p::context.GetRandomNumberGenerator ();
            rnd.GenerateBlock (iv, 16); // random iv
            FillHeaderAndEncrypt (PAYLOAD_TYPE_RELAY_RESPONSE, buf, isV4 ? 64 : 80, introKey, iv, introKey);
            m_Server.Send (buf, isV4 ? 64 : 80, from);
        }   
        LogPrint (eLogDebug, "SSU relay response sent");
    }   

    void SSUSession::SendRelayIntro (SSUSession * session, const boost::asio::ip::udp::endpoint& from)
    {
        if (!session) return;   
        // Alice's address always v4
        if (!from.address ().is_v4 ())
        {
            LogPrint (eLogError, "Alice's IP must be v4");
            return;
        }   
        uint8_t buf[48 + 18] = {};
        uint8_t * payload = buf + sizeof (SSUHeader);
        *payload = 4;
        payload++; // size
        htobe32buf (payload, from.address ().to_v4 ().to_ulong ()); // Alice's IP
        payload += 4; // address    
        htobe16buf (payload, from.port ()); // Alice's port
        payload += 2; // port
        *payload = 0; // challenge size 
        uint8_t iv[16];
        CryptoPP::RandomNumberGenerator& rnd = i2p::context.GetRandomNumberGenerator ();
        rnd.GenerateBlock (iv, 16); // random iv
        FillHeaderAndEncrypt (PAYLOAD_TYPE_RELAY_INTRO, buf, 48, session->m_SessionKey, iv, session->m_MacKey);
        m_Server.Send (buf, 48, session->m_RemoteEndpoint);
        LogPrint (eLogDebug, "SSU relay intro sent");
    }
    
    void SSUSession::ProcessRelayResponse (uint8_t * buf, size_t len)
    {
        LogPrint (eLogDebug, "Relay response received");        
        uint8_t * payload = buf + sizeof (SSUHeader);
        uint8_t remoteSize = *payload; 
        payload++; // remote size
        //boost::asio::ip::address_v4 remoteIP (bufbe32toh (payload));
        payload += remoteSize; // remote address
        //uint16_t remotePort = bufbe16toh (payload);
        payload += 2; // remote port
        uint8_t ourSize = *payload; 
        payload++; // our size
        boost::asio::ip::address ourIP;
        if (ourSize == 4)
        {
            boost::asio::ip::address_v4::bytes_type bytes;
            memcpy (bytes.data (), payload, 4);
            ourIP = boost::asio::ip::address_v4 (bytes);
        }
        else
        {
            boost::asio::ip::address_v6::bytes_type bytes;
            memcpy (bytes.data (), payload, 16);
            ourIP = boost::asio::ip::address_v6 (bytes);
        }
        payload += ourSize; // our address
        uint16_t ourPort = bufbe16toh (payload);
        payload += 2; // our port
        LogPrint ("Our external address is ", ourIP.to_string (), ":", ourPort);
        i2p::context.UpdateAddress (ourIP);
    }

    void SSUSession::ProcessRelayIntro (uint8_t * buf, size_t len)
    {
        uint8_t size = *buf;
        if (size == 4)
        {
            buf++; // size
            boost::asio::ip::address_v4 address (bufbe32toh (buf));
            buf += 4; // address
            uint16_t port = bufbe16toh (buf);
            // send hole punch of 1 byte
            m_Server.Send (buf, 0, boost::asio::ip::udp::endpoint (address, port));
        }
        else
            LogPrint (eLogWarning, "Address size ", size, " is not supported");     
    }       

    void SSUSession::FillHeaderAndEncrypt (uint8_t payloadType, uint8_t * buf, size_t len, 
        const uint8_t * aesKey, const uint8_t * iv, const uint8_t * macKey)
    {   
        if (len < sizeof (SSUHeader))
        {
            LogPrint (eLogError, "Unexpected SSU packet length ", len);
            return;
        }
        //TODO: we are using a dirty solution here but should work for now
        SSUHeader * header = (SSUHeader *)buf;
        memcpy (header->iv, iv, 16);
        header->flag = payloadType << 4; // MSB is 0
        htobe32buf (&(header->time), i2p::util::GetSecondsSinceEpoch ());
        uint8_t * encrypted = &header->flag;
        uint16_t encryptedLen = len - (encrypted - buf);
        i2p::crypto::CBCEncryption encryption(aesKey, iv);
        encryption.Encrypt (encrypted, encryptedLen, encrypted);
        // assume actual buffer size is 18 (16 + 2) bytes more
        memcpy (buf + len, iv, 16);
        htobe16buf (buf + len + 16, encryptedLen);
        i2p::crypto::HMACMD5Digest (encrypted, encryptedLen + 18, macKey, header->mac);
    }

    void SSUSession::FillHeaderAndEncrypt (uint8_t payloadType, uint8_t * buf, size_t len)
    {
        if (len < sizeof (SSUHeader))
        {
            LogPrint (eLogError, "Unexpected SSU packet length ", len);
            return;
        }
        //TODO: we are using a dirty solution here but should work for now
        SSUHeader * header = (SSUHeader *)buf;
        i2p::context.GetRandomNumberGenerator ().GenerateBlock (header->iv, 16); // random iv
        m_SessionKeyEncryption.SetIV (header->iv);
        header->flag = payloadType << 4; // MSB is 0
        htobe32buf (&(header->time), i2p::util::GetSecondsSinceEpoch ());
        uint8_t * encrypted = &header->flag;
        uint16_t encryptedLen = len - (encrypted - buf);
        m_SessionKeyEncryption.Encrypt (encrypted, encryptedLen, encrypted);
        // assume actual buffer size is 18 (16 + 2) bytes more
        memcpy (buf + len, header->iv, 16);
        htobe16buf (buf + len + 16, encryptedLen);
        i2p::crypto::HMACMD5Digest (encrypted, encryptedLen + 18, m_MacKey, header->mac);
    }   
        
    void SSUSession::Decrypt (uint8_t * buf, size_t len, const uint8_t * aesKey)
    {
        if (len < sizeof (SSUHeader))
        {
            LogPrint (eLogError, "Unexpected SSU packet length ", len);
            return;
        }
        //TODO: since we are accessing a uint8_t this is unlikely to crash due to alignment but should be improved
        SSUHeader * header = (SSUHeader *)buf;
        uint8_t * encrypted = &header->flag;
        uint16_t encryptedLen = len - (encrypted - buf);    
        i2p::crypto::CBCDecryption decryption;
        decryption.SetKey (aesKey);
        decryption.SetIV (header->iv);
        decryption.Decrypt (encrypted, encryptedLen, encrypted);
    }

    void SSUSession::DecryptSessionKey (uint8_t * buf, size_t len)
    {
        if (len < sizeof (SSUHeader))
        {
            LogPrint (eLogError, "Unexpected SSU packet length ", len);
            return;
        }
        //TODO: since we are accessing a uint8_t this is unlikely to crash due to alignment but should be improved
        SSUHeader * header = (SSUHeader *)buf;
        uint8_t * encrypted = &header->flag;
        uint16_t encryptedLen = len - (encrypted - buf);    
        if (encryptedLen > 0)
        {   
            m_SessionKeyDecryption.SetIV (header->iv);
            m_SessionKeyDecryption.Decrypt (encrypted, encryptedLen, encrypted);
        }   
    }   
        
    bool SSUSession::Validate (uint8_t * buf, size_t len, const uint8_t * macKey)
    {
        if (len < sizeof (SSUHeader))
        {
            LogPrint (eLogError, "Unexpected SSU packet length ", len);
            return false;
        }
        //TODO: since we are accessing a uint8_t this is unlikely to crash due to alignment but should be improved
        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);
        htobe16buf (buf + len + 16, encryptedLen);
        uint8_t digest[16];
        i2p::crypto::HMACMD5Digest (encrypted, encryptedLen + 18, macKey, digest);
        return !memcmp (header->mac, digest, 16);
    }

    void SSUSession::Connect ()
    {
        if (m_State == eSessionStateUnknown)
        {   
            // set connect timer
            ScheduleConnectTimer ();
            m_DHKeysPair = transports.GetNextDHKeysPair ();
            SendSessionRequest ();
        }   
    }

    void SSUSession::WaitForConnect ()
    {
        if (!m_RemoteRouter) // incoming session
            ScheduleConnectTimer ();
        else
            LogPrint (eLogError, "SSU wait for connect for outgoing session");  
    }

    void SSUSession::ScheduleConnectTimer ()
    {
        m_Timer.cancel ();
        m_Timer.expires_from_now (boost::posix_time::seconds(SSU_CONNECT_TIMEOUT));
        m_Timer.async_wait (std::bind (&SSUSession::HandleConnectTimer,
            shared_from_this (), std::placeholders::_1));   
}

    void SSUSession::HandleConnectTimer (const boost::system::error_code& ecode)
    {
        if (!ecode)
        {
            // timeout expired
            LogPrint ("SSU session was not established after ", SSU_CONNECT_TIMEOUT, " second");
            Failed ();
        }   
    }   
    
    void SSUSession::Introduce (uint32_t iTag, const uint8_t * iKey)
    {
        if (m_State == eSessionStateUnknown)
        {   
            // set connect timer
            m_Timer.expires_from_now (boost::posix_time::seconds(SSU_CONNECT_TIMEOUT));
            m_Timer.async_wait (std::bind (&SSUSession::HandleConnectTimer,
                shared_from_this (), std::placeholders::_1));
        }   
        SendRelayRequest (iTag, iKey);
    }

    void SSUSession::WaitForIntroduction ()
    {
        m_State = eSessionStateIntroduced;
        // set connect timer
        m_Timer.expires_from_now (boost::posix_time::seconds(SSU_CONNECT_TIMEOUT));
        m_Timer.async_wait (std::bind (&SSUSession::HandleConnectTimer,
            shared_from_this (), std::placeholders::_1));           
    }

    void SSUSession::Close ()
    {
        m_State = eSessionStateClosed;
        SendSesionDestroyed ();
        transports.PeerDisconnected (shared_from_this ());
        m_Data.Stop ();
        m_Timer.cancel ();
    }   

    void SSUSession::Done ()
    {
        GetService ().post (std::bind (&SSUSession::Failed, shared_from_this ()));
    }

    void SSUSession::Established ()
    {
        m_State = eSessionStateEstablished;
        if (m_DHKeysPair)
        {
            delete m_DHKeysPair;
            m_DHKeysPair = nullptr;
        }
        m_Data.Start ();
        m_Data.Send (CreateDatabaseStoreMsg ());
        transports.PeerConnected (shared_from_this ());
        if (m_PeerTest && (m_RemoteRouter && m_RemoteRouter->IsPeerTesting ()))
            SendPeerTest ();
        ScheduleTermination ();
    }   

    void SSUSession::Failed ()
    {
        if (m_State != eSessionStateFailed)
        {   
            m_State = eSessionStateFailed;
            m_Server.DeleteSession (shared_from_this ());  
        }   
    }   

    void SSUSession::ScheduleTermination ()
    {
        m_Timer.cancel ();
        m_Timer.expires_from_now (boost::posix_time::seconds(SSU_TERMINATION_TIMEOUT));
        m_Timer.async_wait (std::bind (&SSUSession::HandleTerminationTimer,
            shared_from_this (), std::placeholders::_1));
    }

    void SSUSession::HandleTerminationTimer (const boost::system::error_code& ecode)
    {
        if (ecode != boost::asio::error::operation_aborted)
        {   
            LogPrint ("SSU no activity fo ", SSU_TERMINATION_TIMEOUT, " seconds");
            Failed ();
        }   
    }   
    
    const uint8_t * SSUSession::GetIntroKey () const
    {
        if (m_RemoteRouter)
        {
            // we are client
            auto address = m_RemoteRouter->GetSSUAddress ();
            return address ? (const uint8_t *)address->key : nullptr;
        }
        else
        {
            // we are server
            auto address = i2p::context.GetRouterInfo ().GetSSUAddress ();
            return address ? (const uint8_t *)address->key : nullptr;
        }
    }   

    void SSUSession::SendI2NPMessages (const std::vector<std::shared_ptr<I2NPMessage> >& msgs)
    {
        GetService ().post (std::bind (&SSUSession::PostI2NPMessages, shared_from_this (), msgs));    
    }

    void SSUSession::PostI2NPMessages (std::vector<std::shared_ptr<I2NPMessage> > msgs)
    {
        if (m_State == eSessionStateEstablished)
        {
            for (auto it: msgs)
                if (it) m_Data.Send (it);
        }
    }   

    void SSUSession::ProcessData (uint8_t * buf, size_t len)
    {
        m_Data.ProcessMessage (buf, len);
        m_IsDataReceived = true;
    }

    void SSUSession::FlushData ()
    {
        if (m_IsDataReceived)
        {   
            m_Data.FlushReceivedMessage ();
            m_IsDataReceived = false;
        }       
    }

    void SSUSession::ProcessPeerTest (const uint8_t * buf, size_t len, const boost::asio::ip::udp::endpoint& senderEndpoint)
    {
        uint32_t nonce = bufbe32toh (buf); // 4 bytes
        uint8_t size = buf[4];  // 1 byte   
        uint32_t address = (size == 4) ? buf32toh(buf + 5) : 0; // big endian, size bytes
        uint16_t port = buf16toh(buf + size + 5); // big endian, 2 bytes
        const uint8_t * introKey = buf + size + 7;
        if (port && !address)
        {
            LogPrint (eLogWarning, "Address of ", size, " bytes not supported");    
            return;
        }   
        switch (m_Server.GetPeerTestParticipant (nonce))
        {   
            // existing test 
            case ePeerTestParticipantAlice1:
            {           
                if (m_State == eSessionStateEstablished)
                {
                    LogPrint (eLogDebug, "SSU peer test from Bob. We are Alice");
                    if (i2p::context.GetStatus () == eRouterStatusTesting) // still not OK
                        i2p::context.SetStatus (eRouterStatusFirewalled);
                }
                else
                {
                    LogPrint (eLogDebug, "SSU first peer test from Charlie. We are Alice");
                    i2p::context.SetStatus (eRouterStatusOK);
                    m_Server.UpdatePeerTest (nonce, ePeerTestParticipantAlice2);
                    SendPeerTest (nonce, senderEndpoint.address ().to_v4 ().to_ulong (), 
                        senderEndpoint.port (), introKey, true, false); // to Charlie
                }
                break;
            }   
            case ePeerTestParticipantAlice2:
            {
                if (m_State == eSessionStateEstablished)
                    LogPrint (eLogDebug, "SSU peer test from Bob. We are Alice");
                else
                {
                    // peer test successive
                    LogPrint (eLogDebug, "SSU second peer test from Charlie. We are Alice");
                    i2p::context.SetStatus (eRouterStatusOK);
                    m_Server.RemovePeerTest (nonce);
                }
                break;
            }   
            case ePeerTestParticipantBob: 
            {
                LogPrint (eLogDebug, "SSU peer test from Charlie. We are Bob");
                auto session = m_Server.GetPeerTestSession (nonce); // session with Alice from PeerTest
                if (session && session->m_State == eSessionStateEstablished)
                    session->Send (PAYLOAD_TYPE_PEER_TEST, buf, len); // back to Alice
                m_Server.RemovePeerTest (nonce); // nonce has been used
                break;
            }
            case ePeerTestParticipantCharlie:
            {   
                LogPrint (eLogDebug, "SSU peer test from Alice. We are Charlie");
                SendPeerTest (nonce, senderEndpoint.address ().to_v4 ().to_ulong (),
                    senderEndpoint.port (), introKey); // to Alice with her actual address
                m_Server.RemovePeerTest (nonce); // nonce has been used
                break;
            }
            // test not found   
            case ePeerTestParticipantUnknown:
            {
                if (m_State == eSessionStateEstablished)
                {
                    // new test
                    if (port)
                    {
                        LogPrint (eLogDebug, "SSU peer test from Bob. We are Charlie");
                        m_Server.NewPeerTest (nonce, ePeerTestParticipantCharlie);
                        Send (PAYLOAD_TYPE_PEER_TEST, buf, len); // back to Bob
                        SendPeerTest (nonce, be32toh (address), be16toh (port), introKey); // to Alice with her address received from Bob
                    }
                    else
                    {
                        LogPrint (eLogDebug, "SSU peer test from Alice. We are Bob");
                        auto session = m_Server.GetRandomEstablishedSession (shared_from_this ()); // Charlie
                        if (session)
                        {
                            m_Server.NewPeerTest (nonce, ePeerTestParticipantBob, shared_from_this ());
                            session->SendPeerTest (nonce, senderEndpoint.address ().to_v4 ().to_ulong (),
                                senderEndpoint.port (), introKey, false); // to Charlie with Alice's actual address     
                        }   
                    }
                }
                else
                    LogPrint (eLogError, "SSU unexpected peer test");   
            }
        }   
    }
    
    void SSUSession::SendPeerTest (uint32_t nonce, uint32_t address, uint16_t port, 
        const uint8_t * introKey, bool toAddress, bool sendAddress)
    // toAddress is true for Alice<->Chalie communications only
    // sendAddress is false if message comes from Alice     
    {
        uint8_t buf[80 + 18] = {};
        uint8_t * payload = buf + sizeof (SSUHeader);
        htobe32buf (payload, nonce);
        payload += 4; // nonce  
        // address and port
        if (sendAddress && address)
        {                   
            *payload = 4;
            payload++; // size
            htobe32buf (payload, address);
            payload += 4; // address
        }
        else
        {
            *payload = 0;
            payload++; //size
        }
        htobe16buf (payload, port);
        payload += 2; // port
        // intro key
        if (toAddress)
        {
            // send our intro key to address instead it's own
            auto addr = i2p::context.GetRouterInfo ().GetSSUAddress ();
            if (addr)
                memcpy (payload, addr->key, 32); // intro key
            else
                LogPrint (eLogError, "SSU is not supported. Can't send peer test"); 
        }   
        else    
            memcpy (payload, introKey, 32); // intro key

        // send 
        CryptoPP::RandomNumberGenerator& rnd = i2p::context.GetRandomNumberGenerator ();
        uint8_t iv[16];
        rnd.GenerateBlock (iv, 16); // random iv
        if (toAddress)
        {   
            // encrypt message with specified intro key
            FillHeaderAndEncrypt (PAYLOAD_TYPE_PEER_TEST, buf, 80, introKey, iv, introKey);
            boost::asio::ip::udp::endpoint e (boost::asio::ip::address_v4 (address), port);
            m_Server.Send (buf, 80, e);
        }   
        else
        {
            // encrypt message with session key
            FillHeaderAndEncrypt (PAYLOAD_TYPE_PEER_TEST, buf, 80);
            Send (buf, 80);
        }   
    }   

    void SSUSession::SendPeerTest ()
    {
        // we are Alice
        LogPrint (eLogDebug, "SSU sending peer test");
        auto address = i2p::context.GetRouterInfo ().GetSSUAddress ();
        if (!address)
        {
            LogPrint (eLogError, "SSU is not supported. Can't send peer test");
            return;
        }
        uint32_t nonce = i2p::context.GetRandomNumberGenerator ().GenerateWord32 ();
        if (!nonce) nonce = 1;
        m_PeerTest = false;
        m_Server.NewPeerTest (nonce, ePeerTestParticipantAlice1);
        SendPeerTest (nonce, 0, 0, address->key, false, false); // address and port always zero for Alice
    }   

    void SSUSession::SendKeepAlive ()
    {
        if (m_State == eSessionStateEstablished)
        {   
            uint8_t buf[48 + 18] = {};
            uint8_t * payload = buf + sizeof (SSUHeader);
            *payload = 0; // flags
            payload++;
            *payload = 0; // num fragments  
            // encrypt message with session key
            FillHeaderAndEncrypt (PAYLOAD_TYPE_DATA, buf, 48);
            Send (buf, 48);
            LogPrint (eLogDebug, "SSU keep-alive sent");
            ScheduleTermination ();
        }   
    }

    void SSUSession::SendSesionDestroyed ()
    {
        if (m_IsSessionKey)
        {
            uint8_t buf[48 + 18] = {};
            // encrypt message with session key
            FillHeaderAndEncrypt (PAYLOAD_TYPE_SESSION_DESTROYED, buf, 48);
            try
            {
                Send (buf, 48);
            }
            catch (std::exception& ex)
            {
                LogPrint (eLogError, "SSU send session destoriyed exception ", ex.what ()); 
            }
            LogPrint (eLogDebug, "SSU session destroyed sent");
        }
    }   

    void SSUSession::Send (uint8_t type, const uint8_t * payload, size_t len)
    {
        uint8_t buf[SSU_MTU_V4 + 18] = {};
        size_t msgSize = len + sizeof (SSUHeader); 
        size_t paddingSize = msgSize & 0x0F; // %16
        if (paddingSize > 0) msgSize += (16 - paddingSize);
        if (msgSize > SSU_MTU_V4)
        {
            LogPrint (eLogWarning, "SSU payload size ", msgSize, " exceeds MTU");
            return;
        } 
        memcpy (buf + sizeof (SSUHeader), payload, len);
        // encrypt message with session key
        FillHeaderAndEncrypt (type, buf, msgSize);
        Send (buf, msgSize);
    }           

    void SSUSession::Send (const uint8_t * buf, size_t size)
    {
        m_NumSentBytes += size;
        i2p::transport::transports.UpdateSentBytes (size);
        m_Server.Send (buf, size, m_RemoteEndpoint);
    }   
}
}