Function DecryptFileChunk

src/External/CascLib/src/common/FileStream.cpp:1946–2057

}

static void DecryptFileChunk(
    DWORD * ChunkData,
    LPBYTE pbKey,
    ULONGLONG ByteOffset,
    DWORD dwLength)
{
    ULONGLONG ChunkOffset;
    DWORD KeyShuffled[0x10];
    DWORD KeyMirror[0x10];
    DWORD RoundCount = 0x14;

    // Prepare the key
    ChunkOffset = ByteOffset / ENCRYPTED_CHUNK_SIZE;
    memcpy(KeyMirror, pbKey, ENCRYPTED_CHUNK_SIZE);
    BSWAP_ARRAY32_UNSIGNED(KeyMirror, ENCRYPTED_CHUNK_SIZE);
    KeyMirror[0x05] = (DWORD)(ChunkOffset >> 32);
    KeyMirror[0x08] = (DWORD)(ChunkOffset);

    while(dwLength >= ENCRYPTED_CHUNK_SIZE)
    {
        // Shuffle the key - part 1
        KeyShuffled[0x0E] = KeyMirror[0x00];
        KeyShuffled[0x0C] = KeyMirror[0x01];
        KeyShuffled[0x05] = KeyMirror[0x02];
        KeyShuffled[0x0F] = KeyMirror[0x03];
        KeyShuffled[0x0A] = KeyMirror[0x04];
        KeyShuffled[0x07] = KeyMirror[0x05];
        KeyShuffled[0x0B] = KeyMirror[0x06];
        KeyShuffled[0x09] = KeyMirror[0x07];
        KeyShuffled[0x03] = KeyMirror[0x08];
        KeyShuffled[0x06] = KeyMirror[0x09];
        KeyShuffled[0x08] = KeyMirror[0x0A];
        KeyShuffled[0x0D] = KeyMirror[0x0B];
        KeyShuffled[0x02] = KeyMirror[0x0C];
        KeyShuffled[0x04] = KeyMirror[0x0D];
        KeyShuffled[0x01] = KeyMirror[0x0E];
        KeyShuffled[0x00] = KeyMirror[0x0F];

        // Shuffle the key - part 2
        for(DWORD i = 0; i < RoundCount; i += 2)
        {
            KeyShuffled[0x0A] = KeyShuffled[0x0A] ^ Rol32((KeyShuffled[0x0E] + KeyShuffled[0x02]), 0x07);
            KeyShuffled[0x03] = KeyShuffled[0x03] ^ Rol32((KeyShuffled[0x0A] + KeyShuffled[0x0E]), 0x09);
            KeyShuffled[0x02] = KeyShuffled[0x02] ^ Rol32((KeyShuffled[0x03] + KeyShuffled[0x0A]), 0x0D);
            KeyShuffled[0x0E] = KeyShuffled[0x0E] ^ Rol32((KeyShuffled[0x02] + KeyShuffled[0x03]), 0x12);

            KeyShuffled[0x07] = KeyShuffled[0x07] ^ Rol32((KeyShuffled[0x0C] + KeyShuffled[0x04]), 0x07);
            KeyShuffled[0x06] = KeyShuffled[0x06] ^ Rol32((KeyShuffled[0x07] + KeyShuffled[0x0C]), 0x09);
            KeyShuffled[0x04] = KeyShuffled[0x04] ^ Rol32((KeyShuffled[0x06] + KeyShuffled[0x07]), 0x0D);
            KeyShuffled[0x0C] = KeyShuffled[0x0C] ^ Rol32((KeyShuffled[0x04] + KeyShuffled[0x06]), 0x12);

            KeyShuffled[0x0B] = KeyShuffled[0x0B] ^ Rol32((KeyShuffled[0x05] + KeyShuffled[0x01]), 0x07);
            KeyShuffled[0x08] = KeyShuffled[0x08] ^ Rol32((KeyShuffled[0x0B] + KeyShuffled[0x05]), 0x09);
            KeyShuffled[0x01] = KeyShuffled[0x01] ^ Rol32((KeyShuffled[0x08] + KeyShuffled[0x0B]), 0x0D);
            KeyShuffled[0x05] = KeyShuffled[0x05] ^ Rol32((KeyShuffled[0x01] + KeyShuffled[0x08]), 0x12);

            KeyShuffled[0x09] = KeyShuffled[0x09] ^ Rol32((KeyShuffled[0x0F] + KeyShuffled[0x00]), 0x07);
            KeyShuffled[0x0D] = KeyShuffled[0x0D] ^ Rol32((KeyShuffled[0x09] + KeyShuffled[0x0F]), 0x09);