using ICSharpCode.SharpZipLib.Zip.Compression.Streams;
using Microsoft.Win32;
using System.Security.Cryptography;
using System.Text;

class Program
{
    static void Main()
    {
        var regBytes = (byte[])Registry.GetValue(@"HKEY_CURRENT_USER\Software\Project64", "user", null)!;

        // Back up
        Registry.SetValue(@"HKEY_CURRENT_USER\Software\Project64", "user.bak", regBytes);

        // "Decrypt"
        for (int i = 0; i < regBytes.Length; i++)
        {
            regBytes[i] ^= 0xAA;
        }

        // Expand
        byte[] plainBytes;
        using (var inpStream = new MemoryStream(regBytes))
        using (var outStream = new MemoryStream())
        using (var infStream = new InflaterInputStream(inpStream))
        {
            infStream.CopyTo(outStream);
            plainBytes = outStream.ToArray();
        }

        // As per 2022-02-07, SupportInfo::Validated offset is 1,224
        plainBytes[1224] = 1;

        // Compute Hash
        var md5 = HashAlgorithm.Create("MD5")!;
        var hash = md5.ComputeHash(plainBytes, 0, plainBytes.Length - 32)!;
        var hashString = BitConverter.ToString(hash).Replace("-", "");
        var hashStringBytes = Encoding.ASCII.GetBytes(hashString);
        hashStringBytes.CopyTo(plainBytes, plainBytes.Length - hashStringBytes.Length);

        // Compress
        using (var outStream = new MemoryStream())
        using (var defStream = new DeflaterOutputStream(outStream))
        {
            defStream.Write(plainBytes, 0, plainBytes.Length);
            defStream.Flush();
            defStream.Dispose(); // Else, risk getting an incomplete stream below.

            regBytes = outStream.ToArray();
        }

        // "Encrypt"
        for (int i = 0; i < regBytes.Length; i++)
        {
            regBytes[i] ^= 0xAA;
        }

        // Update registry
        Registry.SetValue(@"HKEY_CURRENT_USER\Software\Project64", "user", regBytes);
    }
}