ok4

using System.Security.Cryptography;
using System.Text;

namespace Aes_Example
{
   class AesExample
   {
      public static void Main()
      {
         Console.WriteLine("Enter password");
         string password = Console.ReadLine(), encrypted64, iv64;
         byte[] hashValue;
         var iv = RandomNumberGenerator.GetBytes(16);
         string text = File.ReadAllText("text.txt");

         hashValue = SHA256.Create().ComputeHash(Encoding.ASCII.GetBytes(password));

         Console.WriteLine("Do you want to <1>encrypt <2>decrypt");
         switch(Convert.ToInt32(Console.ReadLine()))
         {
            case 1:
            {
                try
                {
                    byte[] encrypted = Encrypt(text, hashValue, iv);
                    encrypted64 = Convert.ToBase64String(encrypted, 0, encrypted.Length);
                    iv64 = Convert.ToBase64String(iv, 0, iv.Length);
                    File.WriteAllText("encryptedtext.txt", encrypted64);
                    File.WriteAllText("iv.txt", iv64);
                }
                catch(FileNotFoundException ex)
                {
                    Console.WriteLine($"{ex}");
                }
                break;
            }
            case 2:
            {
                try
                {
                    encrypted64 = File.ReadAllText("encryptedtext.txt");
                    iv64 = File.ReadAllText("iv.txt");
                    byte[] encrypted2 = Convert.FromBase64String(encrypted64);
                    byte[] iv2 = Convert.FromBase64String(iv64);
                    string roundtrip = Decrypt(encrypted2, hashValue, iv2);
                    Console.WriteLine("Decoded text:\n{0}", roundtrip);
                }
                catch(FileNotFoundException ex)
                {
                    Console.WriteLine($"{ex}");
                }
                break;
            }
            default:
            {
                Console.WriteLine("Unknown command");
                break;
            }
         }
      }



      static byte[] Encrypt(string plainText, byte[] Key, byte[] IV)
      {
         if (plainText == null || plainText.Length <= 0)
            throw new ArgumentNullException("plainText");
         if (Key == null || Key.Length <= 0)
            throw new ArgumentNullException("Key");
         if (IV == null || IV.Length <= 0)
            throw new ArgumentNullException("IV");
         byte[] encrypted;

         using (Aes aesAlg = Aes.Create())
         {
            aesAlg.Key = Key;
            aesAlg.IV = IV;
            aesAlg.Mode = CipherMode.CBC;
            aesAlg.Padding = PaddingMode.PKCS7;
            ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);
            using (MemoryStream msEncrypt = new MemoryStream())
            {
               using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
               {
                  using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
                  {
                     swEncrypt.Write(plainText);
                  }
                  encrypted = msEncrypt.ToArray();
               }
            }
         }
         return encrypted;
      }


      static string Decrypt(byte[] cipherText, byte[] Key, byte[] IV)
      {
         if (cipherText == null || cipherText.Length <= 0)
            throw new ArgumentNullException("cipherText");
         if (Key == null || Key.Length <= 0)
            throw new ArgumentNullException("Key");
         if (IV == null || IV.Length <= 0)
            throw new ArgumentNullException("IV");
         string plaintext = null;
         using (Aes aesAlg = Aes.Create())
         {
            aesAlg.Key = Key;
            aesAlg.IV = IV;
            aesAlg.Mode = CipherMode.CBC;
            aesAlg.Padding = PaddingMode.PKCS7;
            ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);
            using (MemoryStream msDecrypt = new MemoryStream(cipherText))
            {
               using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
               {
                  using (StreamReader srDecrypt = new StreamReader(csDecrypt))
                  {
                     plaintext = srDecrypt.ReadToEnd();
                  }
               }
            }
         }

         return plaintext;
      }
   }
}