/// <summary>
/// For traditional decryption
/// </summary>
/// <param name="inStream"></param>
/// <param name="outStream"></param>
/// <param name="seed"></param>
/// <param name="fileSize"></param>
/// <param name="offset"></param>
public void Decrypt(Stream inStream, Stream outStream, uint seed, ulong fileSize, ulong offset)
{
uint crc = ~CRC32.CRC32_0x04C11DB7(_keys.Magic, 0);
uint[] keys = PrepareKey(crc ^ seed, _keys.Key.Data);
byte[] table = GenerateBitsTable(keys);
byte[] buffer = ArrayPool <byte> .Shared.Rent(0x20000);
while (fileSize > 0)
{
ulong bufferSize = fileSize;
if (fileSize > 0x20000)
{
bufferSize = 0x20000;
}
inStream.Position = (long)offset;
inStream.Read(buffer);
DecryptBuffer(buffer, buffer, (int)bufferSize, table, offset);
outStream.Write(buffer.AsSpan(0, (int)bufferSize));
fileSize -= bufferSize;
offset += bufferSize;
}
ArrayPool <byte> .Shared.Return(buffer);
}
/// <summary>
/// Key computing GT5P JP Demo
/// </summary>
/// <param name="seed"></param>
/// <returns></returns>
private uint[] PrepareKeyOld(uint seed)
{
var keysetSeedCrc = ~CRC32.CRC32_0x04C11DB7(_keys.Magic, 0);
uint one = CRC32.CRC32UInt(seed ^ keysetSeedCrc);
uint two = CRC32.CRC32UInt(one);
uint three = CRC32.CRC32UInt(two);
uint four = CRC32.CRC32UInt(three);
uint[] keys = new uint[4];
keys[0] = one & 0x1FFFF;
keys[1] = two & 0x7ffff;
keys[2] = three & 0x7fffff;
keys[3] = four & 0x1fffffff;
return(keys);
}
