using System;

using System.Security.Cryptography;

using System.Text;

​

public class Program

{

    public static string Decrypt(string inputStr)

    {

        string str = "";

        if (inputStr.Length > 16)

        {

            byte[] inputBuffer = Convert.FromBase64String(inputStr);

            byte[] buffer = new byte[16];

            for (int index = 0; index < 16; ++index)

                buffer[index] = inputBuffer[index];

            SHA256CryptoServiceProvider cryptoServiceProvider1 = new SHA256CryptoServiceProvider();

            byte[] hash = cryptoServiceProvider1.ComputeHash(buffer);

            cryptoServiceProvider1.Clear();

            AesCryptoServiceProvider cryptoServiceProvider2 = new AesCryptoServiceProvider();

            cryptoServiceProvider2.Key = hash;

            cryptoServiceProvider2.Mode = CipherMode.ECB;

            cryptoServiceProvider2.Padding = PaddingMode.PKCS7;

            byte[] bytes = cryptoServiceProvider2.CreateDecryptor().TransformFinalBlock(inputBuffer, 16, inputBuffer.Length - 16);

            cryptoServiceProvider2.Clear();

            str = Encoding.UTF8.GetString(bytes);

        }

​

        return str;

    }

​

    public static void Main()

    {

        var encrypted = "base64-style-hash";

        Console.WriteLine($"Decrypted: `{Decrypt(encrypted)}`");

    }

}