Cheat Engine CETRAINER file unpacking

CETRAINER_Unpack.cs

// LinqPad file

// Does not include code initial archive unpacking (CET_Archive.dat)
// File has file names + inflated data chunks, just use offzip - https://aluigi.altervista.org/mytoolz.htm#offzip

void Main()
{
	string baseFolder = "folder";
	
	var data = File.ReadAllBytes(baseFolder + "CET_TRAINER.CETRAINER");
	Decrypt(data);
	
	var magic = Encoding.ASCII.GetString(data.AsSpan(0, 7));
	if (magic != "BRICKES")
		throw new InvalidDataException("Invalid magic");
	
	File.WriteAllBytes(baseFolder + "CET_TRAINER.CETRAINER.dec", data);
	
	byte[] decomp = DecompressFile(data.Skip(7).ToArray()); // Skip magic
	File.WriteAllBytes(baseFolder + "CET_TRAINER.CETRAINER.dec.decomp", decomp);
	
	ProcessCTFile(decomp, baseFolder);
	
}

void ProcessCTFile(byte[] data, string outputDir)
{
	XmlDocument doc = new XmlDocument();

	using var xmlStream = new MemoryStream(data);
	doc.Load(xmlStream);
	var root = doc["CheatTable"];

	// Extract forms and files
	// Forms can be openned with MiTeC DFM Editor - https://www.mitec.cz/dfm.html
	foreach (XmlElement file in root.SelectNodes("Forms")[0])
	{
		var textContent = file.InnerText;
		var fileName = file.Name;
		
		byte[] decodedDataBuffer = new byte[(textContent.Length / 5) * 4 + (textContent.Length % 5)];
		Base85ToBin(textContent, decodedDataBuffer);
		
		byte[] actualFileData = DecompressFile(decodedDataBuffer);
		File.WriteAllBytes(outputDir + ("FORM_" + fileName), actualFileData);
	}

	foreach (XmlElement file in root.SelectNodes("Files")[0])
	{
		var textContent = file.InnerText;
		var fileName = file.Name;

		byte[] decodedDataBuffer = new byte[(textContent.Length / 5) * 4 + (textContent.Length % 5)];
		Base85ToBin(textContent, decodedDataBuffer);

		byte[] actualFileData = DecompressFile(decodedDataBuffer);
		File.WriteAllBytes(outputDir + fileName, actualFileData);
	}
}

// https://github.com/cheat-engine/cheat-engine/blob/dd1f2f83d45d61f7ff692038e322e32bae7fb96e/Cheat%20Engine/OpenSave.pas#L1420
void Decrypt(byte[] data)
{
	int v11 = 2;
	if (data.Length >= 2)
	{
		--v11;
		do
		{
			++v11;
			data[v11] ^= data[v11 - 2];
		}
		while (data.Length - 1 > v11);
	}

	v11 = data.Length - 2;
	if (v11 >= 0)
	{
		++v11;
		do
		{
			--v11;
			data[v11] ^= data[v11 + 1];
		}
		while (v11 > 0);
	}

	byte v10 = 0xCD;
	int v3 = data.Length - 1;
	v11 = 0;
	if (v3 >= 0)
	{
		--v11;
		do
		{
			data[++v11] ^= v10;
			v10 += 2;
		}
		while (v3 > v11);
	}
}

byte[] DecompressFile(byte[] data)
{
	using var ms = new MemoryStream(data.ToArray());
	using var output = new MemoryStream();
	
	using (var ds = new DeflateStream(ms, CompressionMode.Decompress))
	{
		byte[] sizeBuf = new byte[sizeof(int)];
		ds.Read(sizeBuf);
		int uncompSize = BinaryPrimitives.ReadInt32LittleEndian(sizeBuf);
		
		byte[] uncompData = new byte[uncompSize];
		ds.Read(uncompData);
		return uncompData;
	}

}

// https://github.com/cheat-engine/cheat-engine/blob/dd1f2f83d45d61f7ff692038e322e32bae7fb96e/Cheat%20Engine/custombase85.pas#L97
void Base85ToBin(string inputStringBase85, byte[] outData)
{
	const string customBase85 = "0123456789" +
				"ABCDEFGHIJKLMNOPQRSTUVWXYZ" +
				"abcdefghijklmnopqrstuvwxyz" +
				"!#$%()*+,-./:;=?@[]^_{}";
				
	var size = inputStringBase85.Length; 
	var i = 0;
	var j = 0;
	
	var testt = "Hello world".IndexOf("o");
	while (i < size)
	{
		var a = (customBase85.IndexOf(inputStringBase85[i])) * 85 * 85 * 85 * 85;
		i++;
		
		if (i < size)
		{
			a = a + (customBase85.IndexOf(inputStringBase85[i])) * 85 * 85 * 85;
			i++;
		}

		if (i < size)
		{
			a = a + (customBase85.IndexOf(inputStringBase85[i])) * 85 * 85;
			i++;
		}

		if (i < size)
		{
			a = a + (customBase85.IndexOf(inputStringBase85[i])) * 85;
			i++;
		}

		if (i < size)
		{
			a = a + (customBase85.IndexOf(inputStringBase85[i]));
			i++;
			
			outData[j + 0] = (byte)((a >> 24) & 0xFF);
			outData[j + 1] = (byte)((a >> 16) & 0xFF);
			outData[j + 2] = (byte)((a >> 8) & 0xFF);
			outData[j + 3] = (byte)(a & 0xFF);
			j += 4;
		}
		
		switch (size % 5)
		{
			case 2:
				a = a + 84 * 85 * 85 + 84 * 85 * 84;
				outData[j + 0] = (byte)((a >> 24) & 0xFF);
				break;

			case 3:
				a = a 				 + 84 * 85 * 84;
				outData[j + 0] = (byte)((a >> 24) & 0xFF);
				outData[j + 1] = (byte)((a >> 16) & 0xFF);
				break;

			case 4:
				a = a + 						 84;
				outData[j + 0] = (byte)((a >> 24) & 0xFF);
				outData[j + 1] = (byte)((a >> 16) & 0xFF);
				outData[j + 1] = (byte)((a >> 8) & 0xFF);
				break;
		}
	}
}

void GetBytecode()
{
	// Encoding from CE + lua's "encodeFunction" 
	// From https://github.com/cheat-engine/cheat-engine/blob/dd1f2f83d45d61f7ff692038e322e32bae7fb96e/Cheat%20Engine/LuaHandler.pas#L13180
	string luabytecode = "c-n1]%{T;S5XWcf9FpJ^/fMgq6HkJoM]1(3ip4^r!E4!=RTko:Bx$O+6)sTE$yexuY/u#t95w32fnk2k$A4zJS939j-M39_(qD[t:iwUu;}O(uoDrOpGr%r_2sjM5g[;f,Icp4Oua;i,fv2C@z+yLa74($:L[C1n1hBFUmZXyKRs,@BH0$Rtw!{QFf7yo30T_e!eYkO/?@W%I3Bn-8=XW,{v%6dt#Z:[S:#H^Nl]7LdYj5]7TR=A=ipOy[+9mUjDxJh*n#xF{5{iui94$nJF3AZk)-XuvoB6iWj#55W[mUPkef;F;)D({8E?fVc*PM26]xyLZA63Lj.^";

	byte[] decodedDataBuffer = new byte[(luabytecode.Length / 5) * 4 + (luabytecode.Length % 5)];
	Base85ToBin(luabytecode, decodedDataBuffer);

	// Skip 2 bytes and decompress "zlib" to get LuaC bytecode
	// Use LuaDec (might need to compile to the correct version afterwards or you will get a precompiled header chunk error)
	// Check 0x05 once decompressed, indicates the version of the lua compiler i.e 0x53 = 5.3
	// May also need to compile it as x64 if you get a size_t mismatch error
}