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) 2002-2008 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 #include "Statistics.h"
 102
 103 #include <protocol/Protocols.h>
 104 #include <common/MD5Sum.h>
 105
 106 // random generator
 107 #include "CryptoPP_Inc.h"       // Needed for Crypto functions
 108
 109 #define CRYPT_HEADER_WITHOUTPADDING                 8
 110 #define MAGICVALUE_UDP                                          91
 111 #define MAGICVALUE_UDP_SYNC_CLIENT                      0x395F2EC1
 112 #define MAGICVALUE_UDP_SYNC_SERVER                      0x13EF24D5
 113 #define MAGICVALUE_UDP_SERVERCLIENT                     0xA5
 114 #define MAGICVALUE_UDP_CLIENTSERVER                     0x6B
 115
 116 CEncryptedDatagramSocket::CEncryptedDatagramSocket( wxIPaddress &address, wxSocketFlags flags,  const CProxyData *proxyData) : CDatagramSocketProxy(address, flags, proxyData)
 117 {
 118
 119 }
 120
 121 CEncryptedDatagramSocket::~CEncryptedDatagramSocket()
 122 {
 123
 124 }
 125
 126 int CEncryptedDatagramSocket::DecryptReceivedClient(uint8_t *bufIn, int bufLen, uint8_t **bufOut, uint32_t ip, uint32_t *receiverVerifyKey, uint32_t *senderVerifyKey)
 127 {
 128         int result = bufLen;
 129         *bufOut = bufIn;
 130
 131         if (receiverVerifyKey == NULL || senderVerifyKey == NULL) {
 132                 wxFAIL;
 133                 return result;
 134         }
 135
 136         *receiverVerifyKey = 0;
 137         *senderVerifyKey = 0;
 138
 139         if (result <= CRYPT_HEADER_WITHOUTPADDING /*|| !thePrefs.IsClientCryptLayerSupported()*/) {
 140                 return result;
 141         }
 142
 143         switch (bufIn[0]) {
 144                 case OP_EMULEPROT:
 145                 case OP_KADEMLIAPACKEDPROT:
 146                 case OP_KADEMLIAHEADER:
 147                 case OP_UDPRESERVEDPROT1:
 148                 case OP_UDPRESERVEDPROT2:
 149                 case OP_PACKEDPROT:
 150                         return result; // no encrypted packet (see description on top)
 151                 default:
 152                         ;
 153         }
 154
 155         // might be an encrypted packet, try to decrypt
 156         CRC4EncryptableBuffer receivebuffer;
 157         uint32_t value = 0;
 158         // 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
 159         // see the header for marker bits explanation
 160         uint8_t currentTry = ((bufIn[0] & 0x03) == 3) ? 1 : (bufIn[0] & 0x03);
 161         uint8_t tries;
 162         if (Kademlia::CKademlia::GetPrefs() == NULL) {
 163                 // if kad never run, no point in checking anything except for ed2k encryption
 164                 tries = 1;
 165                 currentTry = 1;
 166         } else {
 167                 tries = 3;
 168         }
 169         bool kadRecvKeyUsed = false;
 170         bool kad = false;
 171         do {
 172                 receivebuffer.FullReset();
 173                 tries--;
 174                 MD5Sum md5;
 175
 176                 if (currentTry == 0) {
 177                         // kad packet with NodeID as key
 178                         kad = true;
 179                         kadRecvKeyUsed = false;
 180                         if (Kademlia::CKademlia::GetPrefs()) {
 181                                 uint8_t keyData[18];
 182                                 Kademlia::CKademlia::GetPrefs()->GetKadID().StoreCryptValue((uint8_t *)&keyData);
 183                                 memcpy(keyData + 16, bufIn + 1, 2); // random key part sent from remote client
 184                                 md5.Calculate(keyData, sizeof(keyData));
 185                         }
 186                 } else if (currentTry == 1) {
 187                         // ed2k packet
 188                         kad = false;
 189                         kadRecvKeyUsed = false;
 190                         uint8_t keyData[23];
 191                         md4cpy(keyData, thePrefs::GetUserHash().GetHash());
 192                         keyData[20] = MAGICVALUE_UDP;
 193                         PokeUInt32(keyData + 16, ip);
 194                         memcpy(keyData + 21, bufIn + 1, 2); // random key part sent from remote client
 195                         md5.Calculate(keyData, sizeof(keyData));
 196                 } else if (currentTry == 2) {
 197                         // kad packet with ReceiverKey as key
 198                         kad = true;
 199                         kadRecvKeyUsed = true;
 200                         if (Kademlia::CKademlia::GetPrefs()) {
 201                                 uint8_t keyData[6];
 202                                 PokeUInt32(keyData, Kademlia::CPrefs::GetUDPVerifyKey(ip));
 203                                 memcpy(keyData + 4, bufIn + 1, 2); // random key part sent from remote client
 204                                 md5.Calculate(keyData, sizeof(keyData));
 205                         }
 206                 } else {
 207                         wxFAIL;
 208                 }
 209
 210                 receivebuffer.SetKey(md5, true);
 211                 receivebuffer.RC4Crypt(bufIn + 3, (uint8_t*)&value, sizeof(value));
 212                 ENDIAN_SWAP_I_32(value);
 213
 214                 currentTry = (currentTry + 1) % 3;
 215         } while (value != MAGICVALUE_UDP_SYNC_CLIENT && tries > 0); // try to decrypt as ed2k as well as kad packet if needed (max 3 rounds)
 216
 217         if (value == MAGICVALUE_UDP_SYNC_CLIENT) {
 218                 // yup this is an encrypted packet
 219 //              // debugoutput notices
 220 //              // the following cases are "allowed" but shouldn't happen given that there is only our implementation yet
 221 //              if (bKad && (pbyBufIn[0] & 0x01) != 0)
 222 //                      DebugLog(_T("Received obfuscated UDP packet from clientIP: %s with wrong key marker bits (kad packet, ed2k bit)"), ipstr(dwIP));
 223 //              else if (bKad && !bKadRecvKeyUsed && (pbyBufIn[0] & 0x02) != 0)
 224 //                      DebugLog(_T("Received obfuscated UDP packet from clientIP: %s with wrong key marker bits (kad packet, nodeid key, recvkey bit)"), ipstr(dwIP));
 225 //              else if (bKad && bKadRecvKeyUsed && (pbyBufIn[0] & 0x02) == 0)
 226 //                      DebugLog(_T("Received obfuscated UDP packet from clientIP: %s with wrong key marker bits (kad packet, recvkey key, nodeid bit)"), ipstr(dwIP));
 227
 228                 uint8_t padLen;
 229                 receivebuffer.RC4Crypt(bufIn + 7, (uint8_t*)&padLen, 1);
 230                 result -= CRYPT_HEADER_WITHOUTPADDING;
 231
 232                 if (result <= padLen) {
 233                         //DebugLogError(_T("Invalid obfuscated UDP packet from clientIP: %s, Paddingsize (%u) larger than received bytes"), ipstr(dwIP), byPadLen);
 234                         return bufLen; // pass through, let the Receivefunction do the errorhandling on this junk
 235                 }
 236
 237                 if (padLen > 0) {
 238                         receivebuffer.RC4Crypt(NULL, NULL, padLen);
 239                 }
 240
 241                 result -= padLen;
 242
 243                 if (kad) {
 244                         if (result <= 8) {
 245                                 //DebugLogError(_T("Obfuscated Kad packet with mismatching size (verify keys missing) received from clientIP: %s"), ipstr(dwIP));
 246                                 return bufLen; // pass through, let the Receivefunction do the errorhandling on this junk;
 247                         }
 248                         // read the verify keys
 249                         receivebuffer.RC4Crypt(bufIn + CRYPT_HEADER_WITHOUTPADDING + padLen, (uint8_t*)receiverVerifyKey, 4);
 250                         receivebuffer.RC4Crypt(bufIn + CRYPT_HEADER_WITHOUTPADDING + padLen + 4, (uint8_t*)senderVerifyKey, 4);
 251                         result -= 8;
 252                 }
 253
 254                 *bufOut = bufIn + (bufLen - result);
 255
 256                 receivebuffer.RC4Crypt((uint8_t*)*bufOut, (uint8_t*)*bufOut, result);
 257                 theStats::AddDownOverheadCrypt(bufLen - result);
 258                 return result; // done
 259         } else {
 260                 //DebugLogWarning(_T("Obfuscated packet expected but magicvalue mismatch on UDP packet from clientIP: %s"), ipstr(dwIP));
 261                 return bufLen; // pass through, let the Receivefunction do the errorhandling on this junk
 262         }
 263 }
 264
 265 // Encrypt packet. Key used:
 266 // pachClientHashOrKadID != NULL                                        -> pachClientHashOrKadID
 267 // pachClientHashOrKadID == NULL && bKad && nReceiverVerifyKey != 0     -> nReceiverVerifyKey
 268 // else                                                                 -> ASSERT
 269 int CEncryptedDatagramSocket::EncryptSendClient(uint8_t **buf, int bufLen, const uint8_t *clientHashOrKadID, bool kad, uint32_t receiverVerifyKey, uint32_t senderVerifyKey)
 270 {
 271         wxASSERT(theApp->GetPublicIP() != 0 || kad);
 272         wxASSERT(thePrefs::IsClientCryptLayerSupported());
 273         wxASSERT(clientHashOrKadID != NULL || receiverVerifyKey != 0);
 274         wxASSERT((receiverVerifyKey == 0 && senderVerifyKey == 0) || kad);
 275
 276         uint8_t padLen = 0;                     // padding disabled for UDP currently
 277         const uint32_t cryptHeaderLen = padLen + CRYPT_HEADER_WITHOUTPADDING + (kad ? 8 : 0);
 278         uint32_t cryptedLen = bufLen + cryptHeaderLen;
 279         uint8_t *cryptedBuffer = new uint8_t[cryptedLen];
 280         bool kadRecvKeyUsed = false;
 281
 282         uint16_t randomKeyPart = GetRandomUint16();
 283         CRC4EncryptableBuffer sendbuffer;
 284         MD5Sum md5;
 285         if (kad) {
 286                 if ((clientHashOrKadID == NULL || CMD4Hash(clientHashOrKadID).IsEmpty()) && receiverVerifyKey != 0) {
 287                         kadRecvKeyUsed = true;
 288                         uint8_t keyData[6];
 289                         PokeUInt32(keyData, receiverVerifyKey);
 290                         PokeUInt16(keyData+4, randomKeyPart);
 291                         md5.Calculate(keyData, sizeof(keyData));
 292                         //DEBUG_ONLY( DebugLog(_T("Creating obfuscated Kad packet encrypted by ReceiverKey (%u)"), nReceiverVerifyKey) );
 293                 }
 294                 else if (clientHashOrKadID != NULL && !CMD4Hash(clientHashOrKadID).IsEmpty()) {
 295                         uint8_t keyData[18];
 296                         md4cpy(keyData, clientHashOrKadID);
 297                         PokeUInt16(keyData+16, randomKeyPart);
 298                         md5.Calculate(keyData, sizeof(keyData));
 299                         //DEBUG_ONLY( DebugLog(_T("Creating obfuscated Kad packet encrypted by Hash/NodeID %s"), md4str(pachClientHashOrKadID)) );
 300                 }
 301                 else {
 302                         wxFAIL;
 303                         return bufLen;
 304                 }
 305         } else {
 306                 uint8_t keyData[23];
 307                 md4cpy(keyData, clientHashOrKadID);
 308                 PokeUInt32(keyData+16, theApp->GetPublicIP());
 309                 PokeUInt16(keyData+21, randomKeyPart);
 310                 keyData[20] = MAGICVALUE_UDP;
 311                 md5.Calculate(keyData, sizeof(keyData));
 312         }
 313
 314         sendbuffer.SetKey(md5, true);
 315
 316         // create the semi random byte encryption header
 317         uint8_t semiRandomNotProtocolMarker = 0;
 318         int i;
 319         for (i = 0; i < 128; i++) {
 320                 semiRandomNotProtocolMarker = GetRandomUint8();
 321                 semiRandomNotProtocolMarker = kad ? (semiRandomNotProtocolMarker & 0xFE) : (semiRandomNotProtocolMarker | 0x01); // set the ed2k/kad marker bit
 322                 if (kad) {
 323                         semiRandomNotProtocolMarker = kadRecvKeyUsed ? ((semiRandomNotProtocolMarker & 0xFE) | 0x02) : (semiRandomNotProtocolMarker & 0xFC); // set the ed2k/kad and nodeid/reckey markerbit
 324                 } else {
 325                         semiRandomNotProtocolMarker = (semiRandomNotProtocolMarker | 0x01); // set the ed2k/kad marker bit
 326                 }
 327
 328                 bool bOk = false;
 329                 switch (semiRandomNotProtocolMarker) { // not allowed values
 330                         case OP_EMULEPROT:
 331                         case OP_KADEMLIAPACKEDPROT:
 332                         case OP_KADEMLIAHEADER:
 333                         case OP_UDPRESERVEDPROT1:
 334                         case OP_UDPRESERVEDPROT2:
 335                         case OP_PACKEDPROT:
 336                                 break;
 337                         default:
 338                                 bOk = true;
 339                 }
 340
 341                 if (bOk) {
 342                         break;
 343                 }
 344         }
 345
 346         if (i >= 128) {
 347                 // either we have _real_ bad luck or the randomgenerator is a bit messed up
 348                 wxFAIL;
 349                 semiRandomNotProtocolMarker = 0x01;
 350         }
 351
 352         cryptedBuffer[0] = semiRandomNotProtocolMarker;
 353         PokeUInt16(cryptedBuffer + 1, randomKeyPart);
 354
 355         uint32_t magicValue = ENDIAN_SWAP_32(MAGICVALUE_UDP_SYNC_CLIENT);
 356         sendbuffer.RC4Crypt((uint8_t*)&magicValue, cryptedBuffer + 3, 4);
 357         sendbuffer.RC4Crypt((uint8_t*)&padLen, cryptedBuffer + 7, 1);
 358
 359         for (int j = 0; j < padLen; j++) {
 360                 uint8_t byRand = (uint8_t)rand();       // they actually don't really need to be random, but it doesn't hurt either
 361                 sendbuffer.RC4Crypt((uint8_t*)&byRand, cryptedBuffer + CRYPT_HEADER_WITHOUTPADDING + j, 1);
 362         }
 363
 364         if (kad) {
 365                 sendbuffer.RC4Crypt((uint8_t*)&receiverVerifyKey, cryptedBuffer + CRYPT_HEADER_WITHOUTPADDING + padLen, 4);
 366                 sendbuffer.RC4Crypt((uint8_t*)&senderVerifyKey, cryptedBuffer + CRYPT_HEADER_WITHOUTPADDING + padLen + 4, 4);
 367         }
 368
 369         sendbuffer.RC4Crypt(*buf, cryptedBuffer + cryptHeaderLen, bufLen);
 370         delete [] *buf;
 371         *buf = cryptedBuffer;
 372
 373         theStats::AddUpOverheadCrypt(cryptedLen - bufLen);
 374         return cryptedLen;
 375 }
 376
 377 int CEncryptedDatagramSocket::DecryptReceivedServer(
 378         uint8* pbyBufIn,
 379         int nBufLen, uint8 **ppbyBufOut,
 380         uint32 dwBaseKey,
 381         uint32 /*dbgIP*/)
 382 {
 383         int nResult = nBufLen;
 384         *ppbyBufOut = pbyBufIn;
 385
 386         if (nResult <= CRYPT_HEADER_WITHOUTPADDING || !thePrefs::IsServerCryptLayerUDPEnabled() || dwBaseKey == 0) {
 387                 return nResult;
 388         }
 389
 390         if(pbyBufIn[0] == OP_EDONKEYPROT) {
 391                 return nResult; // no encrypted packet (see description on top)
 392         }
 393
 394         // might be an encrypted packet, try to decrypt
 395         uint8 achKeyData[7];
 396         PokeUInt32(achKeyData, dwBaseKey);
 397         achKeyData[4] = MAGICVALUE_UDP_SERVERCLIENT;
 398         memcpy(achKeyData + 5, pbyBufIn + 1, 2); // random key part sent from remote server
 399
 400         CRC4EncryptableBuffer receivebuffer;
 401         MD5Sum md5(achKeyData, sizeof(achKeyData));
 402         receivebuffer.SetKey(md5,true);
 403
 404         uint32 dwValue;
 405         receivebuffer.RC4Crypt(pbyBufIn + 3, (uint8*)&dwValue, sizeof(dwValue));
 406         ENDIAN_SWAP_I_32(dwValue);
 407         if (dwValue == MAGICVALUE_UDP_SYNC_SERVER){
 408                 // yup this is an encrypted packet
 409                 //DEBUG_ONLY( DebugLog(_T("Received obfuscated UDP packet from ServerIP: %s"), ipstr(dbgIP)) );
 410                 uint8 byPadLen;
 411                 receivebuffer.RC4Crypt(pbyBufIn + 7, (uint8*)&byPadLen, 1);
 412                 byPadLen &= 15;
 413                 nResult -= CRYPT_HEADER_WITHOUTPADDING;
 414
 415                 if (nResult <= byPadLen){
 416                         //DebugLogError(_T("Invalid obfuscated UDP packet from ServerIP: %s, Paddingsize (%u) larger than received bytes"), ipstr(dbgIP), byPadLen);
 417                         return nBufLen; // pass through, let the Receivefunction do the errorhandling on this junk
 418                 }
 419
 420                 if (byPadLen > 0) {
 421                         receivebuffer.RC4Crypt(NULL, NULL, byPadLen);
 422                 }
 423
 424                 nResult -= byPadLen;
 425                 *ppbyBufOut = pbyBufIn + (nBufLen - nResult);
 426                 receivebuffer.RC4Crypt((uint8*)*ppbyBufOut, (uint8*)*ppbyBufOut, nResult);
 427
 428                 theStats::AddDownOverheadCrypt(nBufLen - nResult);
 429                 return nResult; // done
 430         } else {
 431                 //DebugLogWarning(_T("Obfuscated packet expected but magicvalue mismatch on UDP packet from ServerIP: %s"), ipstr(dbgIP));
 432                 return nBufLen; // pass through, let the Receivefunction do the errorhandling on this junk
 433         }
 434 }
 435
 436 int CEncryptedDatagramSocket::EncryptSendServer(uint8** ppbyBuf, int nBufLen, uint32 dwBaseKey) {
 437         wxASSERT( thePrefs::IsServerCryptLayerUDPEnabled() );
 438         wxASSERT( dwBaseKey != 0 );
 439
 440         uint16 nRandomKeyPart = GetRandomUint16();
 441
 442         uint8 achKeyData[7];
 443         PokeUInt32(achKeyData, dwBaseKey);
 444         achKeyData[4] = MAGICVALUE_UDP_CLIENTSERVER;
 445         PokeUInt16(achKeyData + 5, nRandomKeyPart);
 446         MD5Sum md5(achKeyData, sizeof(achKeyData));
 447         CRC4EncryptableBuffer sendbuffer;
 448         sendbuffer.SetKey(md5);
 449
 450         // create the semi random byte encryption header
 451         uint8 bySemiRandomNotProtocolMarker = 0;
 452         int i;
 453
 454         for (i = 0; i < 128; i++){
 455                 bySemiRandomNotProtocolMarker = GetRandomUint8();
 456                 if (bySemiRandomNotProtocolMarker != OP_EDONKEYPROT) { // not allowed values
 457                         break;
 458                 }
 459         }
 460
 461         if (i >= 128){
 462                 // either we have _real_ bad luck or the randomgenerator is a bit messed up
 463                 wxFAIL;
 464                 bySemiRandomNotProtocolMarker = 0x01;
 465         }
 466
 467         uint8 byPadLen = 0;                     // padding disabled for UDP currently
 468         uint32 nCryptedLen = nBufLen + byPadLen + CRYPT_HEADER_WITHOUTPADDING;
 469         uint8* pachCryptedBuffer = new uint8[nCryptedLen];
 470
 471         pachCryptedBuffer[0] = bySemiRandomNotProtocolMarker;
 472         PokeUInt16(pachCryptedBuffer + 1, nRandomKeyPart);
 473
 474         uint32 dwMagicValue = ENDIAN_SWAP_32(MAGICVALUE_UDP_SYNC_SERVER);
 475         sendbuffer.RC4Crypt((uint8*)&dwMagicValue, pachCryptedBuffer + 3, 4);
 476
 477         sendbuffer.RC4Crypt((uint8*)&byPadLen, pachCryptedBuffer + 7, 1);
 478
 479         for (int j = 0; j < byPadLen; j++){
 480                 uint8 byRand = (uint8)rand();   // they actually dont really need to be random, but it doesn't hurts either
 481                 sendbuffer.RC4Crypt((uint8*)&byRand, pachCryptedBuffer + CRYPT_HEADER_WITHOUTPADDING + j, 1);
 482         }
 483         sendbuffer.RC4Crypt(*ppbyBuf, pachCryptedBuffer + CRYPT_HEADER_WITHOUTPADDING + byPadLen, nBufLen);
 484         delete[] *ppbyBuf;
 485         *ppbyBuf = pachCryptedBuffer;
 486
 487         theStats::AddUpOverheadCrypt(nCryptedLen - nBufLen);
 488         return nCryptedLen;
 489 }