using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.IO;
using System.Security.Cryptography;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            //Your code goes here
            Console.WriteLine(AESEncryption.Decrypt("1", "2", "3", "4")); //Пароль (шифруемый текст), пароль для шифрации(ключ), соль, вектор
        }

        public static class AESEncryption
        {
#region Static Functions
            public static string Decrypt(string CipherText, string Password,
                string Salt, string InitialVector,
                string HashAlgorithm = "SHA1", int PasswordIterations = 2,
                int KeySize = 256)
            {
                //if (string.IsNullOrEmpty(CipherText))
                  //  return "";
                byte[] InitialVectorBytes = Encoding.ASCII.GetBytes(InitialVector);
                byte[] SaltValueBytes = Encoding.ASCII.GetBytes(Salt);
                byte[] CipherTextBytes = Convert.FromBase64String(CipherText);

                PasswordDeriveBytes DerivedPassword = new PasswordDeriveBytes(Password, SaltValueBytes, HashAlgorithm, PasswordIterations);
                byte[] KeyBytes = DerivedPassword.GetBytes(KeySize / 8);
                RijndaelManaged SymmetricKey = new RijndaelManaged();
                SymmetricKey.Mode = CipherMode.CBC;
                byte[] PlainTextBytes = new byte[CipherTextBytes.Length];
                int ByteCount = 0;
                using (ICryptoTransform Decryptor = SymmetricKey.CreateDecryptor(KeyBytes, InitialVectorBytes))
                {
                    using (MemoryStream MemStream = new MemoryStream(CipherTextBytes))
                    {
                        using (CryptoStream CryptoStream = new CryptoStream(MemStream, Decryptor, CryptoStreamMode.Read))
                        {

                            ByteCount = CryptoStream.Read(PlainTextBytes, 0, PlainTextBytes.Length);
                            MemStream.Close();
                            CryptoStream.Close();
                        }
                    }
                }
                SymmetricKey.Clear();
                return Encoding.UTF8.GetString(PlainTextBytes, 0, ByteCount);
            }

            #endregion
        }
    }
}