using System;

using System.IO;

using System.Text;

using System.Security.Cryptography;

​

public class Program

{

    public static void Main()

    {

        var keyString = "EkRnG6OK9Zju6fWT86pIal1iKEPnD9E7";

        var decode = false;

        var stringToDecrypt = "z2Oage4aycnP8JZ19BqfmhopYpUUiFrBk075+v/IbOz90+2RWCWMi2lYPizTa/PpSfvwyY8mF5BHSiWy8NegIsFYl5vTtTZpFPTBAAhl/GX/Dd4UhOl0K6svcPNgpa6vjl4NwtIY2zPvcSDdoiio6cKf8ryqwJR1jxOeva6kHrm2v0B1DIniGYj/3VMm6X+MDdj9XPBfZbw73LMLUn1tWbBxiPPRAS/zUwJwsWhCr7I=";

        // Decode URL encoded string if decode is true

        if (decode)

        {

            stringToDecrypt = System.Net.WebUtility.UrlDecode(stringToDecrypt);

        }

​

        // Decrypt the string and print the result

        Console.WriteLine(Decrypt(keyString, stringToDecrypt));

    }

​

    public static string Decrypt(string keyString, string stringToDecrypt)

    {

        // Convert the key string to bytes

        var key = Encoding.UTF8.GetBytes(keyString);

​

        // Replace characters and pad if necessary

        stringToDecrypt = stringToDecrypt.Replace('-', '+').Replace('_', '/');

        switch (stringToDecrypt.Length % 4)

        {

            case 2: stringToDecrypt += "=="; break;

            case 3: stringToDecrypt += "="; break;

        }

​

        // Convert the string to bytes

        var bytes = Convert.FromBase64String(stringToDecrypt);

​

        // Extract IV and text

        var iv = new byte[16];

        var text = new byte[bytes.Length - 16];

        Array.Copy(bytes, iv, 16);

        Array.Copy(bytes, 16, text, 0, text.Length);

​

        // Initialize the plaintext string

        string plaintext = null;

​

        // Decrypt the text

        using (var aes = Aes.Create())

        {

            aes.Padding = PaddingMode.PKCS7;

            aes.IV = iv;

            aes.Key = key;

            aes.Mode = CipherMode.CBC;

​

            // Create a decryptor

            var decryptor = aes.CreateDecryptor(aes.Key, aes.IV);

​

            // Decrypt the text using a CryptoStream

            using (var msDecrypt = new MemoryStream(text))

            {

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

                {

                    using (var srDecrypt = new StreamReader(csDecrypt))

                    {

                        // Read the decrypted text

                        plaintext = srDecrypt.ReadToEnd();

                    }

                }

            }

        }

​

        // Return the decrypted plaintext

        return plaintext;

    }

}

​