/// <summary>
/// Reads the PAK file metadata, including file list information and the file list
/// </summary>
/// <exception cref="NotSupportedException">Is thrown if the given PAK file does not have a valid signature</exception>
private void ReadMetadata()
{
using (BinaryReader reader = new BinaryReader(new MemoryStream(File.ReadAllBytes(FilePath))))
{
reader.BaseStream.Seek(-9L, SeekOrigin.End);
uint fileListOffset = reader.ReadUInt32();
uint fileCount = reader.ReadUInt32();
if ((reader.ReadByte()) != 0x12)
{
throw new NotSupportedException("The signature of this PAK file is invalid!");
}
reader.BaseStream.Seek(fileListOffset, SeekOrigin.Begin);
for (uint i = 0; i < fileCount; i++)
{
FileEntry fileEntry = new FileEntry();
fileEntry.FileNameLength = reader.ReadByte();
fileEntry.Compression = reader.ReadByte();
fileEntry.Offset = reader.ReadUInt32();
fileEntry.FileSize = reader.ReadUInt32();
fileEntry.RealFileSize = reader.ReadUInt32();
byte[] tempName = reader.ReadBytes(fileEntry.FileNameLength);
if (fileEntry.Compression < 4)
{
uint decryptionKey = (uint)Key;
reader.BaseStream.Seek(1L, SeekOrigin.Current);
fileEntry.FileName = Encoding.UTF8.GetString(XOR.Cipher(tempName, decryptionKey));
}
else
{
uint[] decryptionKey = (uint[])Key;
fileEntry.Compression ^= 0x20;
fileEntry.FileName = DecryptFileName(tempName, decryptionKey);
uint[] decryptionData =
{
fileEntry.Offset,
fileEntry.RealFileSize
};
uint[] resultData = XTEA.Decipher(16, decryptionData, decryptionKey);
fileEntry.Offset = resultData[0];
fileEntry.RealFileSize = resultData[1];
}
Entries.Add(fileEntry);
}
}
}
/// <summary>
/// Decrypts the name of a file using XTEA
/// </summary>
/// <param name="fileNameBuffer">Bytes of the file name</param>
/// <param name="key">Key to decrypt the filename with</param>
/// <returns>The decrypted filename</returns>
private static string DecryptFileName(byte[] fileNameBuffer, uint[] key)
{
Span <byte> nameSpan = fileNameBuffer;
for (int j = 0; j < nameSpan.Length; j = j + 8)
{
Span <byte> chunk = nameSpan.Slice(j, 8);
Span <uint> decrypted = XTEA.Decipher(16, MemoryMarshal.Cast <byte, uint>(chunk).ToArray(), key);
Span <byte> resource = MemoryMarshal.AsBytes(decrypted);
resource.CopyTo(chunk);
}
return(Encoding.UTF8.GetString(nameSpan.ToArray().TakeWhile(x => x != 0x00).ToArray()));
}
/// <summary>
/// Reads the file entries of the PAK file
/// </summary>
public void ReadFileEntries()
{
long Position = Reader.BaseStream.Position;
Reader.BaseStream.Seek(FileListOffset, SeekOrigin.Begin);
for (uint i = 0; i < FileCount; i++)
{
FileEntry fileEntry = new FileEntry();
fileEntry.FileNameLength = Reader.ReadByte();
fileEntry.Compression = Reader.ReadByte();
fileEntry.Offset = Reader.ReadUInt32();
fileEntry.FileSize = Reader.ReadUInt32();
fileEntry.RealFileSize = Reader.ReadUInt32();
byte[] tempName = Reader.ReadBytes(fileEntry.FileNameLength);
if (fileEntry.Compression < 4 && fileEntry.Compression > -1)
{
uint decryptionKey = (uint)Key;
fileEntry.Unknown1 = Reader.ReadByte();
fileEntry.FileName = Encoding.UTF8.GetString(XOR.Cipher(tempName, decryptionKey));
}
else
{
uint[] decryptionKey = (uint[])Key;
fileEntry.Compression ^= 0x20;
fileEntry.FileName = DecryptFileName(tempName, decryptionKey);
uint[] decryptionData = new uint[]
{
fileEntry.Offset,
fileEntry.RealFileSize
};
uint[] resultData = XTEA.Decipher(16, decryptionData, decryptionKey);
fileEntry.Offset = resultData[0];
fileEntry.RealFileSize = resultData[1];
}
Entries.Add(fileEntry);
}
Reader.BaseStream.Seek(Position, SeekOrigin.Begin);
}
/// <summary>
/// Decrypts and parses the updatelist file
///
/// Saves the parsed updatelist in the Document instance attribute
/// </summary>
public void Parse()
{
if (DecryptionKey == null)
{
throw new NullReferenceException("DecryptionKey needs to be set using the SetDecryptionKey instance method!");
}
Span <byte> updateList = File.ReadAllBytes(FilePath);
for (int i = 0; i < updateList.Length; i += 8)
{
Span <byte> chunk = updateList.Slice(i, 8);
Span <uint> decrypted = XTEA.Decipher(16, MemoryMarshal.Cast <byte, uint>(chunk).ToArray(), DecryptionKey);
Span <byte> resource = MemoryMarshal.AsBytes(decrypted);
resource.CopyTo(chunk);
}
Document = Encoding.UTF8.GetString(updateList.ToArray());
}
