using System;

using System.Security.Cryptography;

using System.IO;

​

public class Program

{

    public static void Main()

    {

        var decrypter = new Decrypter();

        Console.WriteLine(decrypter.Decrypt(""));

    }

}

public class Decrypter

{

    public string Decrypt(string encryptedString)

    {

        var iv = Convert.FromBase64String(encryptedString.Split('$')[0]);

        var encrypted = Convert.FromBase64String(encryptedString.Split('$')[1]);

        var base64Key = "/3oaB4CloWM7kI5navVllNsDK076d9C1aaFBInGCI04=";

        var key = Convert.FromBase64String(base64Key);

        var decryptedString = DecryptStringFromBytesAes(encrypted, key, iv);

        return decryptedString;

    }

​

    private string DecryptStringFromBytesAes(byte[] cipherText, byte[] Key, byte[] IV)

    {

        // Check arguments.

        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");

        }

​

        // Declare the string used to hold

        // the decrypted text.

        string plaintext = null;

​

        // Create an Aes object

        // with the specified key and IV.

        using (Aes aesAlg = Aes.Create())

        {

            aesAlg.Key = Key;

            aesAlg.IV = IV;

​

            // Create a decryptor to perform the stream transform.

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

​

            // Create the streams used for decryption.

            using (MemoryStream msDecrypt = new MemoryStream(cipherText))

            {

                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();

                    }

                }

            }

        }

​

        return plaintext;

    }

}

​

​