using System;
using System.IO;
using System.Security.Cryptography;
using System.Threading;
using System.Threading.Tasks;

class Program
{
    static void Main(string[] args)
    {
        // Set the path to the directory to encrypt
        string directoryPath = @"C:\MyFolder";

        // Generate a new RSA key pair for the master key
        using (var rsa = new RSACryptoServiceProvider())
        {
            // Save the public key to a file
            File.WriteAllText("public.key", rsa.ToXmlString(false));

            // Save the encrypted private key to a file
            byte[] encryptedPrivateKey = rsa.ExportEncryptedPkcs8PrivateKey(args[0], new PbeParameters(PbeEncryptionAlgorithm.Aes256Cbc, HashAlgorithmName.SHA512, 100000));
            File.WriteAllBytes("private.key", encryptedPrivateKey);
        }

        // Create a thread pool to encrypt files
        int workerThreads, completionPortThreads;
        ThreadPool.GetMaxThreads(out workerThreads, out completionPortThreads);
        ThreadPool.SetMaxThreads(workerThreads, completionPortThreads);

        // Recursively encrypt files in the directory and its subdirectories
        EncryptDirectory(directoryPath);

        Console.WriteLine("Encryption complete.");
        Console.ReadKey();
    }

    static void EncryptDirectory(string directoryPath)
    {
        // Get the files in the directory
        string[] fileNames = Directory.GetFiles(directoryPath);

        // Process each file in a thread pool thread
        foreach (string fileName in fileNames)
        {
            ThreadPool.QueueUserWorkItem(new WaitCallback(EncryptFile), fileName);
        }

        // Recursively process subdirectories in a thread pool thread
        string[] subdirectoryPaths = Directory.GetDirectories(directoryPath);
        foreach (string subdirectoryPath in subdirectoryPaths)
        {
            ThreadPool.QueueUserWorkItem(new WaitCallback(EncryptDirectory), subdirectoryPath);
        }
    }

    static void EncryptFile(object fileNameObject)
    {
        string fileName = (string)fileNameObject;

        // Generate a new AES session key
        using (var aes = new AesCryptoServiceProvider())
        {
            aes.GenerateKey();

            // Encrypt the file with the session key
            using (var inputStream = new FileStream(fileName, FileMode.Open))
            {
                string encryptedFileName = fileName + ".encrypted";
                using (var outputStream = new FileStream(encryptedFileName, FileMode.Create))
                {
                    // Write the encrypted session key to the output stream
                    byte[] encryptedSessionKey = EncryptSessionKey(aes.Key);
                    outputStream.Write(encryptedSessionKey, 0, encryptedSessionKey.Length);

                    // Encrypt the file contents with the session key
                    using (var encryptor = aes.CreateEncryptor())
                    {
                        using (var cryptoStream = new CryptoStream(outputStream, encryptor, CryptoStreamMode.Write))
                        {
                            inputStream.CopyTo(cryptoStream);
                        }
                    }
                }
            }
        }
    }

    static byte[] EncryptSessionKey(byte[] sessionKey)
    {
        // Load the master public key
        string publicKeyXml = File.ReadAllText("public.key");
        using (var rsa = new RSACryptoServiceProvider())
        {
            rsa.FromXmlString(publicKeyXml);

            // Encrypt the session key with the master public key
            return rsa.Encrypt(sessionKey, true);
        }
    }
}