using System;

using System.Text ;

using System.IO;

using  System.Web;

using System.Security.Cryptography;     

public class Program

{

    public static void Main(String[] args)

    {

         byte[] iv = { 1, 2, 3, 4, 5, 6, 6, 5, 4, 3, 2, 1, 7, 7, 7, 7 };

        Teste(128 , 256 , new byte[1] , iv);

    }

    public static void Teste(int BLockSize , int keySize, byte[] key , byte[] iv){

        RijndaelManaged aes = new RijndaelManaged();

        aes.BlockSize = BLockSize;

        string json = @"{ ""cod_contrato"" : ""10"", ""DataInicio"" : ""2018-08-28"", ""DataFinal"": ""2018-08-29"" }";

        string chave = "078348529648661693abf264311a8e56";

        aes.Mode = CipherMode.CBC;

        aes.Padding =  PaddingMode.PKCS7;

        aes.Key = System.Text.Encoding.UTF8.GetBytes(chave);

        aes.IV = iv;

        ICryptoTransform encryptor = aes.CreateEncryptor(aes.Key , aes.IV);

        byte[] encript = encryptor.TransformFinalBlock(ASCIIEncoding.ASCII.GetBytes(json),0,json.Length);

        string str = Convert.ToBase64String(encript);

        Console.WriteLine("Vetor inicial: {0}", iv);

        Console.WriteLine("Encrypted (b64-encode): {0}", str);

        RijndaelManaged aesd = new RijndaelManaged();

        aesd.Mode = CipherMode.CBC;

        aesd.Padding =  PaddingMode.PKCS7;

        aesd.Key = System.Text.Encoding.UTF8.GetBytes(chave);

        aesd.IV = iv;

        ICryptoTransform decryptor = aesd.CreateDecryptor(aesd.Key , aesd.IV);

        byte[] decript = Convert.FromBase64String("y6F0nbQcg3YrO+cMueWnMdTTOCVKYLEtmA7QZT4iNtqmOipRhBsQvcX3VO5sHIz7bK46dnFAvfPf6uAJRA54g0E12Etkf4zMYpW2IgFvyWr5DpZ81QSbI25KO+KgdFxJW1LBY2j8rooDqPxPASiDuQ==");

        string plaintext = null;

        using (MemoryStream msDecrypt = new MemoryStream(decript))

                {

                    using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))

                    {

                        using (StreamReader srDecrypt = new StreamReader(csDecrypt))

                        {

                            // Read the decrypted bytes from the decrypting stream

                            // and place them in a string.

                            plaintext = srDecrypt.ReadToEnd();

                        }

                    }

                }

        Console.WriteLine("Removendo cifragem (b64-encode): {0}", plaintext);

    }

}