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

namespace FileEncryption
{
    class Program
    {
        static void Main(string[] args)
        {
            string inputDirectoryPath = "path/to/input/directory";
            string outputDirectoryPath = "path/to/output/directory";
            string password = "mysecret";

            EncryptDirectory(inputDirectoryPath, outputDirectoryPath, password);
        }

        static void EncryptDirectory(string inputDirectoryPath, string outputDirectoryPath, string password)
        {
            // Get all files in the input directory
            string[] inputFilePaths = Directory.GetFiles(inputDirectoryPath);

            // Create the output directory if it doesn't exist
            if (!Directory.Exists(outputDirectoryPath))
            {
                Directory.CreateDirectory(outputDirectoryPath);
            }

            // Create an array of tasks to encrypt each file in parallel
            Task[] tasks = new Task[inputFilePaths.Length];
            for (int i = 0; i < inputFilePaths.Length; i++)
            {
                string inputFilePath = inputFilePaths[i];
                string outputFilePath = Path.Combine(outputDirectoryPath, Path.GetFileName(inputFilePath));
                tasks[i] = Task.Run(() => EncryptFile(inputFilePath, outputFilePath, password));
            }

            // Wait for all tasks to complete
            Task.WaitAll(tasks);
        }

        static void EncryptFile(string inputFilePath, string outputFilePath, string password)
        {
            using (FileStream inputStream = File.OpenRead(inputFilePath))
            using (FileStream outputStream = File.OpenWrite(outputFilePath))
            using (Aes aes = Aes.Create())
            {
                aes.KeySize = 256;
                aes.BlockSize = 128;
                aes.Mode = CipherMode.CBC;
                aes.Padding = PaddingMode.PKCS7;

                byte[] salt = new byte[16];
                using (RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider())
                {
                    rng.GetBytes(salt);
                }
                aes.GenerateIV();
                byte[] key = new Rfc2898DeriveBytes(password, salt, 10000).GetBytes(32);

                outputStream.Write(salt, 0, salt.Length);
                outputStream.Write(aes.IV, 0, aes.IV.Length);

                using (CryptoStream cryptoStream = new CryptoStream(outputStream, aes.CreateEncryptor(key, aes.IV), CryptoStreamMode.Write))
                {
                    inputStream.CopyTo(cryptoStream);
                }
            }
        }
    }
}