using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

namespace ConsoleApp1
{
    class Program
    {
        public static String decrypt(String cipherText, String password)
        {
            byte[] bufIv = Encoding.UTF8.GetBytes("Kanxue2019CTF-Q1");
            byte[] bufCipher = Convert.FromBase64String(cipherText);
            byte[] bufKey = new PasswordDeriveBytes(password, null).GetBytes(0x20);
            ICryptoTransform transform = new RijndaelManaged { Mode = CipherMode.CBC }.CreateDecryptor(bufKey, bufIv);
            MemoryStream ms = new MemoryStream();
            CryptoStream cs = new CryptoStream(ms, transform, CryptoStreamMode.Write);
            cs.Write(bufCipher, 0, bufCipher.Length);
            cs.FlushFinalBlock();
            String plainText = Encoding.UTF8.GetString(ms.ToArray());
            ms.Close();
            cs.Close();
            return plainText;
        }

        static void Main(string[] args)
        {
            Console.WriteLine(decrypt("4RTlF9Ca2+oqExJwx68FiA==", "Kanxue2019"));
        }
    }
}