src/EncryptedDatagramSocket.cpp

   1 //
   2 // This file is part of the aMule Project.
   3 //
   4 // Copyright (c) 2003-2008 aMule Team ( admin@amule.org / http://www.amule.org )
   5 // Copyright (c) 2002 Merkur ( devs@emule-project.net / http://www.emule-project.net )
   6 //
   7 // Any parts of this program derived from the xMule, lMule or eMule project,
   8 // or contributed by third-party developers are copyrighted by their
   9 // respective authors.
  10 //
  11 // This program is free software; you can redistribute it and/or modify
  12 // it under the terms of the GNU General Public License as published by
  13 // the Free Software Foundation; either version 2 of the License, or
  14 // (at your option) any later version.
  15 //
  16 // This program is distributed in the hope that it will be useful,
  17 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  18 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19 // GNU General Public License for more details.
  20 //
  21 // You should have received a copy of the GNU General Public License
  22 // along with this program; if not, write to the Free Software
  23 // Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA
  24 //
  25
  26 /* Basic Obfusicated Handshake Protocol UDP:
  27         see EncryptedStreamSocket.h
  28
  29 ****************************** ED2K Packets
  30
  31 -Keycreation Client <-> Clinet:
  32         - Client A (Outgoing connection):
  33                 Sendkey: Md5(<UserHashClientB 16><IPClientA 4><MagicValue91 1><RandomKeyPartClientA 2>)  23
  34         - Client B (Incomming connection):
  35                 Receivekey: Md5(<UserHashClientB 16><IPClientA 4><MagicValue91 1><RandomKeyPartClientA 2>)  23
  36          - Note: The first 1024 Bytes will be _NOT_ discarded for UDP keys to safe CPU time
  37
  38         - Handshake
  39                 -> The handshake is encrypted - except otherwise noted - by the Keys created above
  40                 -> Padding is cucrently not used for UDP meaning that PaddingLen will be 0, using PaddingLens up to 16 Bytes is acceptable however
  41                 Client A: <SemiRandomNotProtocolMarker 7 Bits[Unencrypted]><ED2K Marker 1Bit = 1><RandomKeyPart 2[Unencrypted]><MagicValue 4><PaddingLen 1><RandomBytes PaddingLen%16>
  42
  43         - Additional Comments:
  44                 - For obvious reasons the UDP handshake is actually no handshake. If a different Encryption method (or better a different Key) is to be used this has to be negotiated in a TCP connection
  45                 - SemiRandomNotProtocolMarker is a Byte which has a value unequal any Protocol header byte. This is a compromiss, turning in complete randomness (and nice design) but gaining a lower CPU usage
  46                 - Kad/Ed2k Marker are only indicators, which possibility could be tried first, and should not be trusted
  47
  48 ****************************** Server Packets
  49
  50 -Keycreation Client <-> Server:
  51         - Client A (Outgoing connection client -> server):
  52                 Sendkey: Md5(<BaseKey 4><MagicValueClientServer 1><RandomKeyPartClientA 2>)  7
  53         - Client B (Incomming connection):
  54                 Receivekey: Md5(<BaseKey 4><MagicValueServerClient 1><RandomKeyPartClientA 2>)  7
  55         - Note: The first 1024 Bytes will be _NOT_ discarded for UDP keys to safe CPU time
  56
  57         - Handshake
  58                 -> The handshake is encrypted - except otherwise noted - by the Keys created above
  59                 -> Padding is cucrently not used for UDP meaning that PaddingLen will be 0, using PaddingLens up to 16 Bytes is acceptable however
  60                 Client A: <SemiRandomNotProtocolMarker 1[Unencrypted]><RandomKeyPart 2[Unencrypted]><MagicValue 4><PaddingLen 1><RandomBytes PaddingLen%16>
  61
  62         - Overhead: 8 Bytes per UDP Packet
  63
  64         - Security for Basic Obfusication:
  65                 - Random looking packets, very limited protection against passive eavesdropping single packets
  66
  67         - Additional Comments:
  68                 - For obvious reasons the UDP handshake is actually no handshake. If a different Encryption method (or better a different Key) is to be used this has to be negotiated in a TCP connection
  69                 - SemiRandomNotProtocolMarker is a Byte which has a value unequal any Protocol header byte. This is a compromiss, turning in complete randomness (and nice design) but gaining a lower CPU usage
  70
  71 ****************************** KAD Packets
  72
  73 -Keycreation Client <-> Client:
  74         - Client A (Outgoing connection):
  75                 Sendkey: Md5(<KadID 16><RandomKeyPartClientA 2>)  18
  76         - Client B (Incomming connection):
  77                 Receivekey: Md5(<KadID 16><RandomKeyPartClientA 2>)  18
  78         - Note: The first 1024 Bytes will be _NOT_ discarded for UDP keys to safe CPU time
  79
  80         - Handshake
  81                 -> The handshake is encrypted - except otherwise noted - by the Keys created above
  82                 -> Padding is cucrently not used for UDP meaning that PaddingLen will be 0, using PaddingLens up to 16 Bytes is acceptable however
  83                 Client A: <SemiRandomNotProtocolMarker 7 Bits[Unencrypted]><Kad Marker 1Bit = 0><RandomKeyPart 2[Unencrypted]><MagicValue 4><PaddingLen 1><RandomBytes PaddingLen%16><ReceiverVerifyKey 2><SenderVerifyKey 2>
  84
  85         - Overhead: 12 Bytes per UDP Packet
  86
  87         - Additional Comments:
  88                 - For obvious reasons the UDP handshake is actually no handshake. If a different Encryption method (or better a different Key) is to be used this has to be negotiated in a TCP connection
  89                 - SemiRandomNotProtocolMarker is a Byte which has a value unequal any Protocol header byte. This is a compromiss, turning in complete randomness (and nice design) but gaining a lower CPU usage
  90                 - Kad/Ed2k Marker are only indicators, which possibility could be tried first, and should not be trusted
  91 */
  92
  93 #include "EncryptedDatagramSocket.h"
  94 #include "amule.h"
  95 #include "Logger.h"
  96 #include "Preferences.h"
  97 #include "RC4Encrypt.h"
  98 #include "./kademlia/kademlia/Prefs.h"
  99 #include "./kademlia/kademlia/Kademlia.h"
 100 #include "RandomFunctions.h"
 101
 102 #include <protocol/Protocols.h>
 103 #include <common/MD5Sum.h>
 104
 105 // random generator
 106 #include "CryptoPP_Inc.h"       // Needed for Crypto functions
 107
 108 #define CRYPT_HEADER_WITHOUTPADDING                 8
 109 #define MAGICVALUE_UDP                                          91
 110 #define MAGICVALUE_UDP_SYNC_CLIENT                      0x395F2EC1
 111 #define MAGICVALUE_UDP_SYNC_SERVER                      0x13EF24D5
 112 #define MAGICVALUE_UDP_SERVERCLIENT                     0xA5
 113 #define MAGICVALUE_UDP_CLIENTSERVER                     0x6B
 114
 115 CEncryptedDatagramSocket::CEncryptedDatagramSocket( wxIPaddress &address, wxSocketFlags flags,  const CProxyData *proxyData) : CDatagramSocketProxy(address, flags, proxyData)
 116 {
 117
 118 }
 119
 120 CEncryptedDatagramSocket::~CEncryptedDatagramSocket()
 121 {
 122
 123 }
 124
 125 int CEncryptedDatagramSocket::DecryptReceivedClient(uint8_t *bufIn, int bufLen, uint8_t **bufOut, uint32_t ip, uint32_t *receiverVerifyKey, uint32_t *senderVerifyKey)
 126 {
 127         int result = bufLen;
 128         *bufOut = bufIn;
 129
 130         if (receiverVerifyKey == NULL || senderVerifyKey == NULL) {
 131                 wxFAIL;
 132                 return result;
 133         }
 134
 135         *receiverVerifyKey = 0;
 136         *senderVerifyKey = 0;
 137
 138         if (result <= CRYPT_HEADER_WITHOUTPADDING /*|| !thePrefs.IsClientCryptLayerSupported()*/) {
 139                 return result;
 140         }
 141
 142         switch (bufIn[0]) {
 143                 case OP_EMULEPROT:
 144                 case OP_KADEMLIAPACKEDPROT:
 145                 case OP_KADEMLIAHEADER:
 146                 case OP_UDPRESERVEDPROT1:
 147                 case OP_UDPRESERVEDPROT2:
 148                 case OP_PACKEDPROT:
 149                         return result; // no encrypted packet (see description on top)
 150                 default:
 151                         ;
 152         }
 153
 154         // might be an encrypted packet, try to decrypt
 155         CRC4EncryptableBuffer receivebuffer;
 156         uint32_t value = 0;
 157         // check the marker bit which type this packet could be and which key to test first, this is only an indicator since old clients have it set random
 158         // see the header for marker bits explanation
 159         uint8_t currentTry = ((bufIn[0] & 0x03) == 3) ? 1 : (bufIn[0] & 0x03);
 160         uint8_t tries;
 161         if (Kademlia::CKademlia::GetPrefs() == NULL) {
 162                 // if kad never run, no point in checking anything except for ed2k encryption
 163                 tries = 1;
 164                 currentTry = 1;
 165         } else {
 166                 tries = 3;
 167         }
 168         bool kadRecvKeyUsed = false;
 169         bool kad = false;
 170         do {
 171                 receivebuffer.FullReset();
 172                 tries--;
 173                 MD5Sum md5;
 174
 175                 if (currentTry == 0) {
 176                         // kad packet with NodeID as key
 177                         kad = true;
 178                         kadRecvKeyUsed = false;
 179                         if (Kademlia::CKademlia::GetPrefs()) {
 180                                 uint8_t keyData[18];
 181                                 Kademlia::CKademlia::GetPrefs()->GetKadID().StoreCryptValue((uint8_t *)&keyData);
 182                                 memcpy(keyData + 16, bufIn + 1, 2); // random key part sent from remote client
 183                                 md5.Calculate(keyData, sizeof(keyData));
 184                         }
 185                 } else if (currentTry == 1) {
 186                         // ed2k packet
 187                         kad = false;
 188                         kadRecvKeyUsed = false;
 189                         uint8_t keyData[23];
 190                         md4cpy(keyData, thePrefs::GetUserHash().GetHash());
 191                         keyData[20] = MAGICVALUE_UDP;
 192                         PokeUInt32(keyData + 16, ip);
 193                         memcpy(keyData + 21, bufIn + 1, 2); // random key part sent from remote client
 194                         md5.Calculate(keyData, sizeof(keyData));
 195                 } else if (currentTry == 2) {
 196                         // kad packet with ReceiverKey as key
 197                         kad = true;
 198                         kadRecvKeyUsed = true;
 199                         if (Kademlia::CKademlia::GetPrefs()) {
 200                                 uint8_t keyData[6];
 201                                 PokeUInt32(keyData, Kademlia::CPrefs::GetUDPVerifyKey(ip));
 202                                 memcpy(keyData + 4, bufIn + 1, 2); // random key part sent from remote client
 203                                 md5.Calculate(keyData, sizeof(keyData));
 204                         }
 205                 } else {
 206                         wxFAIL;
 207                 }
 208
 209                 receivebuffer.SetKey(md5, true);
 210                 receivebuffer.RC4Crypt(bufIn + 3, (uint8_t*)&value, sizeof(value));
 211                 ENDIAN_SWAP_I_32(value);
 212
 213                 currentTry = (currentTry + 1) % 3;
 214         } while (value != MAGICVALUE_UDP_SYNC_CLIENT && tries > 0); // try to decrypt as ed2k as well as kad packet if needed (max 3 rounds)
 215
 216         if (value == MAGICVALUE_UDP_SYNC_CLIENT) {
 217                 // yup this is an encrypted packet
 218 //              // debugoutput notices
 219 //              // the following cases are "allowed" but shouldn't happen given that there is only our implementation yet
 220 //              if (bKad && (pbyBufIn[0] & 0x01) != 0)
 221 //                      DebugLog(_T("Received obfuscated UDP packet from clientIP: %s with wrong key marker bits (kad packet, ed2k bit)"), ipstr(dwIP));
 222 //              else if (bKad && !bKadRecvKeyUsed && (pbyBufIn[0] & 0x02) != 0)
 223 //                      DebugLog(_T("Received obfuscated UDP packet from clientIP: %s with wrong key marker bits (kad packet, nodeid key, recvkey bit)"), ipstr(dwIP));
 224 //              else if (bKad && bKadRecvKeyUsed && (pbyBufIn[0] & 0x02) == 0)
 225 //                      DebugLog(_T("Received obfuscated UDP packet from clientIP: %s with wrong key marker bits (kad packet, recvkey key, nodeid bit)"), ipstr(dwIP));
 226
 227                 uint8_t padLen;
 228                 receivebuffer.RC4Crypt(bufIn + 7, (uint8_t*)&padLen, 1);
 229                 result -= CRYPT_HEADER_WITHOUTPADDING;
 230
 231                 if (result <= padLen) {
 232                         //DebugLogError(_T("Invalid obfuscated UDP packet from clientIP: %s, Paddingsize (%u) larger than received bytes"), ipstr(dwIP), byPadLen);
 233                         return bufLen; // pass through, let the Receivefunction do the errorhandling on this junk
 234                 }
 235
 236                 if (padLen > 0) {
 237                         receivebuffer.RC4Crypt(NULL, NULL, padLen);
 238                 }
 239
 240                 result -= padLen;
 241
 242                 if (kad) {
 243                         if (result <= 8) {
 244                                 //DebugLogError(_T("Obfuscated Kad packet with mismatching size (verify keys missing) received from clientIP: %s"), ipstr(dwIP));
 245                                 return bufLen; // pass through, let the Receivefunction do the errorhandling on this junk;
 246                         }
 247                         // read the verify keys
 248                         receivebuffer.RC4Crypt(bufIn + CRYPT_HEADER_WITHOUTPADDING + padLen, (uint8_t*)receiverVerifyKey, 4);
 249                         receivebuffer.RC4Crypt(bufIn + CRYPT_HEADER_WITHOUTPADDING + padLen + 4, (uint8_t*)senderVerifyKey, 4);
 250                         result -= 8;
 251                 }
 252
 253                 *bufOut = bufIn + (bufLen - result);
 254
 255                 receivebuffer.RC4Crypt((uint8_t*)*bufOut, (uint8_t*)*bufOut, result);
 256                 //theStats::AddDownDataOverheadCrypt(bufLen - result);
 257                 return result; // done
 258         } else {
 259                 //DebugLogWarning(_T("Obfuscated packet expected but magicvalue mismatch on UDP packet from clientIP: %s"), ipstr(dwIP));
 260                 return bufLen; // pass through, let the Receivefunction do the errorhandling on this junk
 261         }
 262 }
 263
 264 // Encrypt packet. Key used:
 265 // pachClientHashOrKadID != NULL                                        -> pachClientHashOrKadID
 266 // pachClientHashOrKadID == NULL && bKad && nReceiverVerifyKey != 0     -> nReceiverVerifyKey
 267 // else                                                                 -> ASSERT
 268 int CEncryptedDatagramSocket::EncryptSendClient(uint8_t **buf, int bufLen, const uint8_t *clientHashOrKadID, bool kad, uint32_t receiverVerifyKey, uint32_t senderVerifyKey)
 269 {
 270         wxASSERT(theApp->GetPublicIP() != 0 || kad);
 271         wxASSERT(thePrefs::IsClientCryptLayerSupported());
 272         wxASSERT(clientHashOrKadID != NULL || receiverVerifyKey != 0);
 273         wxASSERT((receiverVerifyKey == 0 && senderVerifyKey == 0) || kad);
 274
 275         uint8_t padLen = 0;                     // padding disabled for UDP currently
 276         const uint32_t cryptHeaderLen = padLen + CRYPT_HEADER_WITHOUTPADDING + (kad ? 8 : 0);
 277         uint32_t cryptedLen = bufLen + cryptHeaderLen;
 278         uint8_t *cryptedBuffer = new uint8_t[cryptedLen];
 279         bool kadRecvKeyUsed = false;
 280
 281         uint16_t randomKeyPart = GetRandomUint16();
 282         CRC4EncryptableBuffer sendbuffer;
 283         MD5Sum md5;
 284         if (kad) {
 285                 if ((clientHashOrKadID == NULL || CMD4Hash(clientHashOrKadID).IsEmpty()) && receiverVerifyKey != 0) {
 286                         kadRecvKeyUsed = true;
 287                         uint8_t keyData[6];
 288                         PokeUInt32(keyData, receiverVerifyKey);
 289                         PokeUInt16(keyData+4, randomKeyPart);
 290                         md5.Calculate(keyData, sizeof(keyData));
 291                         //DEBUG_ONLY( DebugLog(_T("Creating obfuscated Kad packet encrypted by ReceiverKey (%u)"), nReceiverVerifyKey) );
 292                 }
 293                 else if (clientHashOrKadID != NULL && !CMD4Hash(clientHashOrKadID).IsEmpty()) {
 294                         uint8_t keyData[18];
 295                         md4cpy(keyData, clientHashOrKadID);
 296                         PokeUInt16(keyData+16, randomKeyPart);
 297                         md5.Calculate(keyData, sizeof(keyData));
 298                         //DEBUG_ONLY( DebugLog(_T("Creating obfuscated Kad packet encrypted by Hash/NodeID %s"), md4str(pachClientHashOrKadID)) );
 299                 }
 300                 else {
 301                         wxFAIL;
 302                         return bufLen;
 303                 }
 304         } else {
 305                 uint8_t keyData[23];
 306                 md4cpy(keyData, clientHashOrKadID);
 307                 PokeUInt32(keyData+16, theApp->GetPublicIP());
 308                 PokeUInt16(keyData+21, randomKeyPart);
 309                 keyData[20] = MAGICVALUE_UDP;
 310                 md5.Calculate(keyData, sizeof(keyData));
 311         }
 312
 313         sendbuffer.SetKey(md5, true);
 314
 315         // create the semi random byte encryption header
 316         uint8_t semiRandomNotProtocolMarker = 0;
 317         int i;
 318         for (i = 0; i < 128; i++) {
 319                 semiRandomNotProtocolMarker = GetRandomUint8();
 320                 semiRandomNotProtocolMarker = kad ? (semiRandomNotProtocolMarker & 0xFE) : (semiRandomNotProtocolMarker | 0x01); // set the ed2k/kad marker bit
 321                 if (kad) {
 322                         semiRandomNotProtocolMarker = kadRecvKeyUsed ? ((semiRandomNotProtocolMarker & 0xFE) | 0x02) : (semiRandomNotProtocolMarker & 0xFC); // set the ed2k/kad and nodeid/reckey markerbit
 323                 } else {
 324                         semiRandomNotProtocolMarker = (semiRandomNotProtocolMarker | 0x01); // set the ed2k/kad marker bit
 325                 }
 326
 327                 bool bOk = false;
 328                 switch (semiRandomNotProtocolMarker) { // not allowed values
 329                         case OP_EMULEPROT:
 330                         case OP_KADEMLIAPACKEDPROT:
 331                         case OP_KADEMLIAHEADER:
 332                         case OP_UDPRESERVEDPROT1:
 333                         case OP_UDPRESERVEDPROT2:
 334                         case OP_PACKEDPROT:
 335                                 break;
 336                         default:
 337                                 bOk = true;
 338                 }
 339
 340                 if (bOk) {
 341                         break;
 342                 }
 343         }
 344
 345         if (i >= 128) {
 346                 // either we have _real_ bad luck or the randomgenerator is a bit messed up
 347                 wxFAIL;
 348                 semiRandomNotProtocolMarker = 0x01;
 349         }
 350
 351         cryptedBuffer[0] = semiRandomNotProtocolMarker;
 352         PokeUInt16(cryptedBuffer + 1, randomKeyPart);
 353
 354         uint32_t magicValue = ENDIAN_SWAP_32(MAGICVALUE_UDP_SYNC_CLIENT);
 355         sendbuffer.RC4Crypt((uint8_t*)&magicValue, cryptedBuffer + 3, 4);
 356         sendbuffer.RC4Crypt((uint8_t*)&padLen, cryptedBuffer + 7, 1);
 357
 358         for (int j = 0; j < padLen; j++) {
 359                 uint8_t byRand = (uint8_t)rand();       // they actually don't really need to be random, but it doesn't hurt either
 360                 sendbuffer.RC4Crypt((uint8_t*)&byRand, cryptedBuffer + CRYPT_HEADER_WITHOUTPADDING + j, 1);
 361         }
 362
 363         if (kad) {
 364                 sendbuffer.RC4Crypt((uint8_t*)&receiverVerifyKey, cryptedBuffer + CRYPT_HEADER_WITHOUTPADDING + padLen, 4);
 365                 sendbuffer.RC4Crypt((uint8_t*)&senderVerifyKey, cryptedBuffer + CRYPT_HEADER_WITHOUTPADDING + padLen + 4, 4);
 366         }
 367
 368         sendbuffer.RC4Crypt(*buf, cryptedBuffer + cryptHeaderLen, bufLen);
 369         delete [] *buf;
 370         *buf = cryptedBuffer;
 371
 372         //theStats::AddUpDataOverheadCrypt(cryptedLen - bufLen);
 373         return cryptedLen;
 374 }
 375
 376 int CEncryptedDatagramSocket::DecryptReceivedServer(
 377         uint8* pbyBufIn,
 378         int nBufLen, uint8 **ppbyBufOut,
 379         uint32 dwBaseKey,
 380         uint32 /*dbgIP*/)
 381 {
 382         int nResult = nBufLen;
 383         *ppbyBufOut = pbyBufIn;
 384
 385         if (nResult <= CRYPT_HEADER_WITHOUTPADDING || !thePrefs::IsServerCryptLayerUDPEnabled() || dwBaseKey == 0) {
 386                 return nResult;
 387         }
 388
 389         if(pbyBufIn[0] == OP_EDONKEYPROT) {
 390                 return nResult; // no encrypted packet (see description on top)
 391         }
 392
 393         // might be an encrypted packet, try to decrypt
 394         uint8 achKeyData[7];
 395         PokeUInt32(achKeyData, dwBaseKey);
 396         achKeyData[4] = MAGICVALUE_UDP_SERVERCLIENT;
 397         memcpy(achKeyData + 5, pbyBufIn + 1, 2); // random key part sent from remote server
 398
 399         CRC4EncryptableBuffer receivebuffer;
 400         MD5Sum md5(achKeyData, sizeof(achKeyData));
 401         receivebuffer.SetKey(md5,true);
 402
 403         uint32 dwValue;
 404         receivebuffer.RC4Crypt(pbyBufIn + 3, (uint8*)&dwValue, sizeof(dwValue));
 405         ENDIAN_SWAP_I_32(dwValue);
 406         if (dwValue == MAGICVALUE_UDP_SYNC_SERVER){
 407                 // yup this is an encrypted packet
 408                 //DEBUG_ONLY( DebugLog(_T("Received obfuscated UDP packet from ServerIP: %s"), ipstr(dbgIP)) );
 409                 uint8 byPadLen;
 410                 receivebuffer.RC4Crypt(pbyBufIn + 7, (uint8*)&byPadLen, 1);
 411                 byPadLen &= 15;
 412                 nResult -= CRYPT_HEADER_WITHOUTPADDING;
 413
 414                 if (nResult <= byPadLen){
 415                         //DebugLogError(_T("Invalid obfuscated UDP packet from ServerIP: %s, Paddingsize (%u) larger than received bytes"), ipstr(dbgIP), byPadLen);
 416                         return nBufLen; // pass through, let the Receivefunction do the errorhandling on this junk
 417                 }
 418
 419                 if (byPadLen > 0) {
 420                         receivebuffer.RC4Crypt(NULL, NULL, byPadLen);
 421                 }
 422
 423                 nResult -= byPadLen;
 424                 *ppbyBufOut = pbyBufIn + (nBufLen - nResult);
 425                 receivebuffer.RC4Crypt((uint8*)*ppbyBufOut, (uint8*)*ppbyBufOut, nResult);
 426
 427                 //theStats.AddDownDataOverheadCrypt(nBufLen - nResult);
 428                 return nResult; // done
 429         } else {
 430                 //DebugLogWarning(_T("Obfuscated packet expected but magicvalue mismatch on UDP packet from ServerIP: %s"), ipstr(dbgIP));
 431                 return nBufLen; // pass through, let the Receivefunction do the errorhandling on this junk
 432         }
 433 }
 434
 435 int CEncryptedDatagramSocket::EncryptSendServer(uint8** ppbyBuf, int nBufLen, uint32 dwBaseKey) {
 436         wxASSERT( thePrefs::IsServerCryptLayerUDPEnabled() );
 437         wxASSERT( dwBaseKey != 0 );
 438
 439         uint8 byPadLen = 0;                     // padding disabled for UDP currently
 440         uint32 nCryptedLen = nBufLen + byPadLen + CRYPT_HEADER_WITHOUTPADDING;
 441         uint8* pachCryptedBuffer = new uint8[nCryptedLen];
 442
 443         uint16 nRandomKeyPart = GetRandomUint16();
 444
 445         uint8 achKeyData[7];
 446         PokeUInt32(achKeyData, dwBaseKey);
 447         achKeyData[4] = MAGICVALUE_UDP_CLIENTSERVER;
 448         PokeUInt16(achKeyData + 5, nRandomKeyPart);
 449         MD5Sum md5(achKeyData, sizeof(achKeyData));
 450         CRC4EncryptableBuffer sendbuffer;
 451         sendbuffer.SetKey(md5);
 452
 453         // create the semi random byte encryption header
 454         uint8 bySemiRandomNotProtocolMarker = 0;
 455         int i;
 456
 457         for (i = 0; i < 128; i++){
 458                 bySemiRandomNotProtocolMarker = GetRandomUint8();
 459                 if (bySemiRandomNotProtocolMarker != OP_EDONKEYPROT) { // not allowed values
 460                         break;
 461                 }
 462         }
 463
 464         if (i >= 128){
 465                 // either we have _real_ bad luck or the randomgenerator is a bit messed up
 466                 wxASSERT( false );
 467                 bySemiRandomNotProtocolMarker = 0x01;
 468         }
 469
 470         pachCryptedBuffer[0] = bySemiRandomNotProtocolMarker;
 471         PokeUInt16(pachCryptedBuffer + 1, nRandomKeyPart);
 472
 473         uint32 dwMagicValue = ENDIAN_SWAP_32(MAGICVALUE_UDP_SYNC_SERVER);
 474         sendbuffer.RC4Crypt((uint8*)&dwMagicValue, pachCryptedBuffer + 3, 4);
 475
 476         sendbuffer.RC4Crypt((uint8*)&byPadLen, pachCryptedBuffer + 7, 1);
 477
 478         for (int j = 0; j < byPadLen; j++){
 479                 uint8 byRand = (uint8)rand();   // they actually dont really need to be random, but it doesn't hurts either
 480                 sendbuffer.RC4Crypt((uint8*)&byRand, pachCryptedBuffer + CRYPT_HEADER_WITHOUTPADDING + j, 1);
 481         }
 482         sendbuffer.RC4Crypt(*ppbyBuf, pachCryptedBuffer + CRYPT_HEADER_WITHOUTPADDING + byPadLen, nBufLen);
 483         delete[] *ppbyBuf;
 484         *ppbyBuf = pachCryptedBuffer;
 485
 486         //theStats.AddUpDataOverheadCrypt(nCryptedLen - nBufLen);
 487         return nCryptedLen;
 488 }