Encrypt-Decrypt String, C#

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using System;
using System.Text;
using System.Security.Cryptography;
using System.IO;
using System.Linq;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var key = "z20ds5898a4e5523bbce3ea1025a1916";  
                
            var encryptedString = EncryptString(key, "enter your string here");  
            Console.WriteLine($"encrypted string = {encryptedString}");  
  
            Console.WriteLine("--------------------------------------------------------------------------------------------");  
            var decryptedString = DecryptString(key, encryptedString);  
            Console.WriteLine($"decrypted string = {decryptedString}");  
   
        }
        public static string EncryptString(string key, string plainText)  
        {  
            byte[] iv = new byte[16];  
            byte[] array;  
  
            using (Aes aes = Aes.Create())  
            {  
                aes.Key = Encoding.UTF8.GetBytes(key);  
                aes.IV = iv;  
  
                ICryptoTransform encryptor = aes.CreateEncryptor(aes.Key, aes.IV);  
  
                using (MemoryStream memoryStream = new MemoryStream())  
                {  
                    using (CryptoStream cryptoStream = new CryptoStream((Stream)memoryStream, encryptor, CryptoStreamMode.Write))  
                    {  
                        using (StreamWriter streamWriter = new StreamWriter((Stream)cryptoStream))  
                        {  
                            streamWriter.Write(plainText);  
                        }  
  
                        array = memoryStream.ToArray();  
                    }  
                }  
            }  
  
            return Convert.ToBase64String(array);  
        }  
  
        public static string DecryptString(string key, string cipherText)  
        {  
            byte[] iv = new byte[16];  
            byte[] buffer = Convert.FromBase64String(cipherText);  
  
            using (Aes aes = Aes.Create())  
            {  
                aes.Key = Encoding.UTF8.GetBytes(key);  
                aes.IV = iv;  
                ICryptoTransform decryptor = aes.CreateDecryptor(aes.Key, aes.IV);  
  
                using (MemoryStream memoryStream = new MemoryStream(buffer))  
                {  
                    using (CryptoStream cryptoStream = new CryptoStream((Stream)memoryStream, decryptor, CryptoStreamMode.Read))  
                    {  
                        using (StreamReader streamReader = new StreamReader((Stream)cryptoStream))  
                        {  
                            return streamReader.ReadToEnd();  
                        }  
                    }  
                }  
            }  
        }

private static byte[] Generate256BitsOfRandomEntropy()
        {
            var randomBytes = new byte[32]; // 32 Bytes will give us 256 bits.
            using (var rngCsp = new RNGCryptoServiceProvider())
            {
                // Fill the array with cryptographically secure random bytes.
                rngCsp.GetBytes(randomBytes);
            }
            return randomBytes;
        }
        
    }
}

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Compilation time: 0,25 sec, absolute running time: 0,13 sec, cpu time: 0,12 sec, average memory usage: 14 Mb, average nr of threads: 2, absolute service time: 0,4 sec