/*****************************************************************************/ /* CascDecrypt.cpp Copyright (c) Ladislav Zezula 2015 */ /*---------------------------------------------------------------------------*/ /* Decryption functions for CascLib */ /*---------------------------------------------------------------------------*/ /* Date Ver Who Comment */ /* -------- ---- --- ------- */ /* 31.10.15 1.00 Lad The first version of CascDecrypt.cpp */ /*****************************************************************************/ #define __CASCLIB_SELF__ #include "CascLib.h" #include "CascCommon.h" //----------------------------------------------------------------------------- // Local structures typedef struct _CASC_ENCRYPTION_KEY { ULONGLONG KeyName; // "Name" of the key BYTE Key[0x10]; // The key itself } CASC_ENCRYPTION_KEY, *PCASC_ENCRYPTION_KEY; typedef struct _CASC_SALSA20 { DWORD Key[0x10]; DWORD dwRounds; } CASC_SALSA20, *PCASC_SALSA20; //----------------------------------------------------------------------------- // Local variables //keyName FB680CB6A8BF81F3 key 62D90EFA7F36D71C398AE2F1FE37BDB9 keyNameSize 8 keySize 16 //keyName 402CD9D8D6BFED98 key AEB0EADEA47612FE6C041A03958DF241 keyNameSize 8 keySize 16 //keyName 87AEBBC9C4E6B601 key 685E86C6063DFDA6C9E85298076B3D42 keyNameSize 8 keySize 16 //keyName A19C4F859F6EFA54 key 0196CB6F5ECBAD7CB5283891B9712B4B keyNameSize 8 keySize 16 //keyName 11A9203C9881710A key 2E2CB8C397C2F24ED0B5E452F18DC267 keyNameSize 8 keySize 16 //keyName DBD3371554F60306 key 34E397ACE6DD30EEFDC98A2AB093CD3C keyNameSize 8 keySize 16 //keyName DEE3A0521EFF6F03 key AD740CE3FFFF9231468126985708E1B9 keyNameSize 8 keySize 16 //keyName 8C9106108AA84F07 key 53D859DDA2635A38DC32E72B11B32F29 keyNameSize 8 keySize 16 static CASC_ENCRYPTION_KEY CascKeys[] = { {0xFB680CB6A8BF81F3ULL, {0x62, 0xD9, 0x0E, 0xFA, 0x7F, 0x36, 0xD7, 0x1C, 0x39, 0x8A, 0xE2, 0xF1, 0xFE, 0x37, 0xBD, 0xB9}}, {0x402CD9D8D6BFED98ULL, {0xAE, 0xB0, 0xEA, 0xDE, 0xA4, 0x76, 0x12, 0xFE, 0x6C, 0x04, 0x1A, 0x03, 0x95, 0x8D, 0xF2, 0x41}}, {0x87AEBBC9C4E6B601ULL, {0x68, 0x5E, 0x86, 0xC6, 0x06, 0x3D, 0xFD, 0xA6, 0xC9, 0xE8, 0x52, 0x98, 0x07, 0x6B, 0x3D, 0x42}}, {0xA19C4F859F6EFA54ULL, {0x01, 0x96, 0xCB, 0x6F, 0x5E, 0xCB, 0xAD, 0x7C, 0xB5, 0x28, 0x38, 0x91, 0xB9, 0x71, 0x2B, 0x4B}}, {0x11A9203C9881710AULL, {0x2E, 0x2C, 0xB8, 0xC3, 0x97, 0xC2, 0xF2, 0x4E, 0xD0, 0xB5, 0xE4, 0x52, 0xF1, 0x8D, 0xC2, 0x67}}, {0xDBD3371554F60306ULL, {0x34, 0xE3, 0x97, 0xAC, 0xE6, 0xDD, 0x30, 0xEE, 0xFD, 0xC9, 0x8A, 0x2A, 0xB0, 0x93, 0xCD, 0x3C}}, {0xDEE3A0521EFF6F03ULL, {0xAD, 0x74, 0x0C, 0xE3, 0xFF, 0xFF, 0x92, 0x31, 0x46, 0x81, 0x26, 0x98, 0x57, 0x08, 0xE1, 0xB9}}, {0x8C9106108AA84F07ULL, {0x53, 0xD8, 0x59, 0xDD, 0xA2, 0x63, 0x5A, 0x38, 0xDC, 0x32, 0xE7, 0x2B, 0x11, 0xB3, 0x2F, 0x29}}, {0x49166D358A34D815ULL, {0x66, 0x78, 0x68, 0xCD, 0x94, 0xEA, 0x01, 0x35, 0xB9, 0xB1, 0x6C, 0x93, 0xB1, 0x12, 0x4A, 0xBA}}, {0, {0}} }; static const char * szKeyConstant16 = "expand 16-byte k"; static const char * szKeyConstant32 = "expand 32-byte k"; //----------------------------------------------------------------------------- // Local functions static DWORD Rol32(DWORD dwValue, DWORD dwRolCount) { return (dwValue << dwRolCount) | (dwValue >> (32 - dwRolCount)); } static LPBYTE FindCascKey(ULONGLONG KeyName) { // Search the known keys for(size_t i = 0; CascKeys[i].KeyName != 0; i++) { if(CascKeys[i].KeyName == KeyName) return CascKeys[i].Key; } // Key not found return NULL; } static void Initialize(PCASC_SALSA20 pState, LPBYTE pbKey, DWORD cbKeyLength, LPBYTE pbVector) { const char * szConstants = (cbKeyLength == 32) ? szKeyConstant32 : szKeyConstant16; DWORD KeyIndex = cbKeyLength - 0x10; memset(pState, 0, sizeof(CASC_SALSA20)); pState->Key[0] = *(PDWORD)(szConstants + 0x00); pState->Key[1] = *(PDWORD)(pbKey + 0x00); pState->Key[2] = *(PDWORD)(pbKey + 0x04); pState->Key[3] = *(PDWORD)(pbKey + 0x08); pState->Key[4] = *(PDWORD)(pbKey + 0x0C); pState->Key[5] = *(PDWORD)(szConstants + 0x04); pState->Key[6] = *(PDWORD)(pbVector + 0x00); pState->Key[7] = *(PDWORD)(pbVector + 0x04); pState->Key[8] = 0; pState->Key[9] = 0; pState->Key[10] = *(PDWORD)(szConstants + 0x08); pState->Key[11] = *(PDWORD)(pbKey + KeyIndex + 0x00); pState->Key[12] = *(PDWORD)(pbKey + KeyIndex + 0x04); pState->Key[13] = *(PDWORD)(pbKey + KeyIndex + 0x08); pState->Key[14] = *(PDWORD)(pbKey + KeyIndex + 0x0C); pState->Key[15] = *(PDWORD)(szConstants + 0x0C); pState->dwRounds = 20; } static int Decrypt(PCASC_SALSA20 pState, LPBYTE pbOutBuffer, LPBYTE pbInBuffer, size_t cbInBuffer) { LPBYTE pbXorValue; DWORD KeyMirror[0x10]; DWORD XorValue[0x10]; DWORD BlockSize; DWORD i; // Repeat until we have data to read while(cbInBuffer > 0) { // Create the copy of the key memcpy(KeyMirror, pState->Key, sizeof(KeyMirror)); // Shuffle the key for(i = 0; i < pState->dwRounds; i += 2) { KeyMirror[0x04] ^= Rol32((KeyMirror[0x00] + KeyMirror[0x0C]), 0x07); KeyMirror[0x08] ^= Rol32((KeyMirror[0x04] + KeyMirror[0x00]), 0x09); KeyMirror[0x0C] ^= Rol32((KeyMirror[0x08] + KeyMirror[0x04]), 0x0D); KeyMirror[0x00] ^= Rol32((KeyMirror[0x0C] + KeyMirror[0x08]), 0x12); KeyMirror[0x09] ^= Rol32((KeyMirror[0x05] + KeyMirror[0x01]), 0x07); KeyMirror[0x0D] ^= Rol32((KeyMirror[0x09] + KeyMirror[0x05]), 0x09); KeyMirror[0x01] ^= Rol32((KeyMirror[0x0D] + KeyMirror[0x09]), 0x0D); KeyMirror[0x05] ^= Rol32((KeyMirror[0x01] + KeyMirror[0x0D]), 0x12); KeyMirror[0x0E] ^= Rol32((KeyMirror[0x0A] + KeyMirror[0x06]), 0x07); KeyMirror[0x02] ^= Rol32((KeyMirror[0x0E] + KeyMirror[0x0A]), 0x09); KeyMirror[0x06] ^= Rol32((KeyMirror[0x02] + KeyMirror[0x0E]), 0x0D); KeyMirror[0x0A] ^= Rol32((KeyMirror[0x06] + KeyMirror[0x02]), 0x12); KeyMirror[0x03] ^= Rol32((KeyMirror[0x0F] + KeyMirror[0x0B]), 0x07); KeyMirror[0x07] ^= Rol32((KeyMirror[0x03] + KeyMirror[0x0F]), 0x09); KeyMirror[0x0B] ^= Rol32((KeyMirror[0x07] + KeyMirror[0x03]), 0x0D); KeyMirror[0x0F] ^= Rol32((KeyMirror[0x0B] + KeyMirror[0x07]), 0x12); KeyMirror[0x01] ^= Rol32((KeyMirror[0x00] + KeyMirror[0x03]), 0x07); KeyMirror[0x02] ^= Rol32((KeyMirror[0x01] + KeyMirror[0x00]), 0x09); KeyMirror[0x03] ^= Rol32((KeyMirror[0x02] + KeyMirror[0x01]), 0x0D); KeyMirror[0x00] ^= Rol32((KeyMirror[0x03] + KeyMirror[0x02]), 0x12); KeyMirror[0x06] ^= Rol32((KeyMirror[0x05] + KeyMirror[0x04]), 0x07); KeyMirror[0x07] ^= Rol32((KeyMirror[0x06] + KeyMirror[0x05]), 0x09); KeyMirror[0x04] ^= Rol32((KeyMirror[0x07] + KeyMirror[0x06]), 0x0D); KeyMirror[0x05] ^= Rol32((KeyMirror[0x04] + KeyMirror[0x07]), 0x12); KeyMirror[0x0B] ^= Rol32((KeyMirror[0x0A] + KeyMirror[0x09]), 0x07); KeyMirror[0x08] ^= Rol32((KeyMirror[0x0B] + KeyMirror[0x0A]), 0x09); KeyMirror[0x09] ^= Rol32((KeyMirror[0x08] + KeyMirror[0x0B]), 0x0D); KeyMirror[0x0A] ^= Rol32((KeyMirror[0x09] + KeyMirror[0x08]), 0x12); KeyMirror[0x0C] ^= Rol32((KeyMirror[0x0F] + KeyMirror[0x0E]), 0x07); KeyMirror[0x0D] ^= Rol32((KeyMirror[0x0C] + KeyMirror[0x0F]), 0x09); KeyMirror[0x0E] ^= Rol32((KeyMirror[0x0D] + KeyMirror[0x0C]), 0x0D); KeyMirror[0x0F] ^= Rol32((KeyMirror[0x0E] + KeyMirror[0x0D]), 0x12); } // Set the number of remaining bytes pbXorValue = (LPBYTE)XorValue; BlockSize = (DWORD)CASCLIB_MIN(cbInBuffer, 0x40); // Prepare the XOR constants for(i = 0; i < 16; i++) { XorValue[i] = KeyMirror[i] + pState->Key[i]; } // Decrypt the block for(i = 0; i < BlockSize; i++) { pbOutBuffer[i] = pbInBuffer[i] ^ pbXorValue[i]; } pState->Key[8] = pState->Key[8] + 1; if(pState->Key[8] == 0) pState->Key[9] = pState->Key[9] + 1; // Adjust buffers pbOutBuffer += BlockSize; pbInBuffer += BlockSize; cbInBuffer -= BlockSize; } return ERROR_SUCCESS; } static int Decrypt_Salsa20(LPBYTE pbOutBuffer, LPBYTE pbInBuffer, size_t cbInBuffer, LPBYTE pbKey, DWORD cbKeySize, LPBYTE pbVector) { CASC_SALSA20 SalsaState; Initialize(&SalsaState, pbKey, cbKeySize, pbVector); return Decrypt(&SalsaState, pbOutBuffer, pbInBuffer, cbInBuffer); } //----------------------------------------------------------------------------- // Public functions int CascDecrypt(LPBYTE pbOutBuffer, PDWORD pcbOutBuffer, LPBYTE pbInBuffer, DWORD cbInBuffer, DWORD dwFrameIndex) { ULONGLONG KeyName = 0; LPBYTE pbBufferEnd = pbInBuffer + cbInBuffer; LPBYTE pbKey; DWORD KeyNameSize; DWORD dwShift = 0; DWORD IVSize; BYTE Vector[0x08]; BYTE EncryptionType; int nError; // Verify and retrieve the key name size if(pbInBuffer >= pbBufferEnd) return ERROR_FILE_CORRUPT; if(pbInBuffer[0] != 0 && pbInBuffer[0] != 8) return ERROR_NOT_SUPPORTED; KeyNameSize = *pbInBuffer++; // Copy the key name if((pbInBuffer + KeyNameSize) >= pbBufferEnd) return ERROR_FILE_CORRUPT; memcpy(&KeyName, pbInBuffer, KeyNameSize); pbInBuffer += KeyNameSize; // Verify and retrieve the Vector size if(pbInBuffer >= pbBufferEnd) return ERROR_FILE_CORRUPT; if(pbInBuffer[0] != 4 && pbInBuffer[0] != 8) return ERROR_NOT_SUPPORTED; IVSize = *pbInBuffer++; // Copy the initialization vector if((pbInBuffer + IVSize) >= pbBufferEnd) return ERROR_FILE_CORRUPT; memset(Vector, 0, sizeof(Vector)); memcpy(Vector, pbInBuffer, IVSize); pbInBuffer += IVSize; // Verify and retrieve the encryption type if(pbInBuffer >= pbBufferEnd) return ERROR_FILE_CORRUPT; if(pbInBuffer[0] != 'S' && pbInBuffer[0] != 'A') return ERROR_NOT_SUPPORTED; EncryptionType = *pbInBuffer++; // Do we have enough space in the output buffer? if((DWORD)(pbBufferEnd - pbInBuffer) > pcbOutBuffer[0]) return ERROR_INSUFFICIENT_BUFFER; // Check if we know the key pbKey = FindCascKey(KeyName); if(pbKey == NULL) return ERROR_FILE_ENCRYPTED; // Shuffle the Vector with the block index // Note that there's no point to go beyond 32 bits, unless the file has // more than 0xFFFFFFFF frames. for(int i = 0; i < sizeof(dwFrameIndex); i++) { Vector[i] = Vector[i] ^ (BYTE)((dwFrameIndex >> dwShift) & 0xFF); dwShift += 8; } // Perform the decryption-specific action switch(EncryptionType) { case 'S': // Salsa20 nError = Decrypt_Salsa20(pbOutBuffer, pbInBuffer, (pbBufferEnd - pbInBuffer), pbKey, 0x10, Vector); if(nError != ERROR_SUCCESS) return nError; // Supply the size of the output buffer pcbOutBuffer[0] = (DWORD)(pbBufferEnd - pbInBuffer); return ERROR_SUCCESS; // case 'A': // return ERROR_NOT_SUPPORTED; } assert(false); return ERROR_NOT_SUPPORTED; } int CascDirectCopy(LPBYTE pbOutBuffer, PDWORD pcbOutBuffer, LPBYTE pbInBuffer, DWORD cbInBuffer) { // Check the buffer size if((cbInBuffer - 1) > pcbOutBuffer[0]) return ERROR_INSUFFICIENT_BUFFER; // Copy the data memcpy(pbOutBuffer, pbInBuffer, cbInBuffer); pcbOutBuffer[0] = cbInBuffer; return ERROR_SUCCESS; }