public static bool DecryptNisasyst(FileInfo input, string path, FileInfo output)
{
using (FileStream fileStream = input.OpenRead())
using (StreamReader streamReader = new StreamReader(fileStream))
{
// Test the file length
if (fileStream.Length <= 8)
{
// This can't be a valid file
return(false);
}
// Seek to the magic numbers
fileStream.Seek(-8, SeekOrigin.End);
// Verify the magic numbers
if (streamReader.ReadToEnd() != MagicNumbers)
{
// This isn't a valid file
return(false);
}
// Generate a CRC32 over the game path
Crc32 crc32 = new Crc32();
uint seed = crc32.Get(Encoding.ASCII.GetBytes(path));
// Create a new SeadRandom instance using the seed
SeadRandom seadRandom = new SeadRandom(seed);
// Create the encryption key and IV
byte[] encryptionKey = CreateSequence(seadRandom);
byte[] iv = CreateSequence(seadRandom);
using (MemoryStream memoryStream = new MemoryStream())
using (AesManaged cryptor = new AesManaged())
{
cryptor.Mode = CipherMode.CBC;
cryptor.Padding = PaddingMode.PKCS7;
cryptor.KeySize = 128;
cryptor.BlockSize = 128;
using (CryptoStream cryptoStream = new CryptoStream(memoryStream, cryptor.CreateDecryptor(encryptionKey, iv), CryptoStreamMode.Write))
{
// Seek to the beginning of the file
fileStream.Seek(0, SeekOrigin.Begin);
// Copy the encrypted data
CopyStream(fileStream, cryptoStream, (int)fileStream.Length - 8);
}
// Write out the new file
byte[] outputBytes = memoryStream.ToArray();
output.Directory.Create();
using (FileStream outputStream = output.Create())
outputStream.Write(outputBytes, 0, outputBytes.Length);
return(true);
}
}
}
private static byte[] CreateSequence(SeadRandom random)
{
// Create byte array
byte[] sequence = new byte[16];
// Create each byte
for (int i = 0; i < sequence.Length; i++)
{
// Create empty byte string
string byteString = "";// "0x";
// Get characters from key material
byteString += KeyMaterialString[(int)(random.GetUInt32() >> 24)];
byteString += KeyMaterialString[(int)(random.GetUInt32() >> 24)];
// Parse the resulting byte
sequence[i] = Convert.ToByte(byteString, 16);
}
// Return the sequence
return(sequence);
}