Encrypt.cs

// See https://aka.ms/new-console-template for more information

using System.Reflection;
using System.Runtime.CompilerServices;
using System.Runtime.Loader;
using System.Security.Cryptography;

internal class Program
{
    private static async Task Main(string[] args)
    {
        EncryptFile();

        do
        {
            ExecuteInline(out var asmWRef);
            int gcCount = 0;

            while(asmWRef.IsAlive && (++gcCount < 10))
            {
                GC.Collect();
                GC.WaitForPendingFinalizers();
            }
            Console.WriteLine($"assembly unloaded [{gcCount}]");
            await Task.Delay(60_000);
            
        } while(true);
    }

    [MethodImpl(MethodImplOptions.NoInlining)]
    private static void ExecuteInline(out WeakReference asmWRef)
    {
        var ctx = new EncryptedLoadContext();
        var asm = ctx.LoadFromAssemblyName(new AssemblyName
        {
            Name = "impl"
        });

        var type = asm.DefinedTypes.First(x => x.Name.Contains("MyClass"));
        Console.WriteLine(type);
        var method = type.GetMethod("Execute", BindingFlags.Static | BindingFlags.Public);
        Console.WriteLine(method);


        method!.Invoke(null, Array.Empty<object>());

        asmWRef = new WeakReference(ctx, trackResurrection: true);
        ctx.Unload();
    }

    private static void EncryptFile()
    {
        using var aes = Aes.Create();

        // TODO: use real key and IV
        aes.KeySize = 256;
        aes.IV = Convert.FromHexString("392822A5BCFC47ABED338F8745C9F5DD");
        aes.Key = Convert.FromHexString("2B3E5DDB832115976DC416D09A371E95B6698D5E7AEE906C7946C6AD16939140");

        using var fs = File.OpenRead(@"C:\dev\sleep\impl\bin\Debug\net7.0\impl.dll");
        using var outFs = File.Open(@"C:\temp\dll.bin", FileMode.Truncate, FileAccess.ReadWrite);
        using var cs = new CryptoStream(outFs, aes.CreateEncryptor(), CryptoStreamMode.Write);

        fs.CopyTo(cs);
        cs.Flush();
    }
}

public class EncryptedLoadContext : AssemblyLoadContext
{
    public EncryptedLoadContext() : base(isCollectible: true)
    {
    }

    protected override Assembly? Load(AssemblyName name)
    {
        if (!name.Name.Contains("impl")) return base.Load(name);

        using var aes = Aes.Create();

        aes.KeySize = 256;
        aes.IV = Convert.FromHexString("392822A5BCFC47ABED338F8745C9F5DD");
        aes.Key = Convert.FromHexString("2B3E5DDB832115976DC416D09A371E95B6698D5E7AEE906C7946C6AD16939140");

        using var fs = File.OpenRead(@"C:\temp\dll.bin");
        using var cs = new CryptoStream(fs, aes.CreateDecryptor(), CryptoStreamMode.Read);
        using var ms = new MemoryStream();
        cs.CopyTo(ms);

        ms.Seek(0, SeekOrigin.Begin);

        return LoadFromStream(ms);
    }

}