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

namespace Showlicense
{
    internal static class AesHelper
    {
        /// <summary>
        /// "Vinno.vCloud.CurrentLicense" two MD5
        /// </summary>
        private const string Key = "2A4A2B05EFD02D5BDEBB55711213BBBD";
        /// <summary>
        ///  Gets Decrypt text
        /// </summary>
        /// <param name="inputText"></param>
        /// <returns></returns>
        internal static string Decrypt(string inputText)
        {
            return AesDecrypt(inputText, Key);
        }
        /// <summary>
        /// AES algorithm  Decrypt string
        /// </summary>
        /// <param name="cipherText"></param>
        /// <param name="keyString">AES Key</param>
        /// <returns></returns>
        private static string AesDecrypt(string cipherText, string keyString)
        {
            var fullCipher = Convert.FromBase64String(cipherText);

            byte[] iv = new byte[16];

            var cipher = new byte[fullCipher.Length - iv.Length];

            Buffer.BlockCopy(fullCipher, 0, iv, 0, iv.Length);
            Buffer.BlockCopy(fullCipher, iv.Length, cipher, 0, fullCipher.Length - iv.Length);
            var key = Encoding.UTF8.GetBytes(keyString);

            using (var aesAlg = Aes.Create())
            {
                using (var decryptor = aesAlg.CreateDecryptor(key, iv))
                {
                    string result;
                    using (var msDecrypt = new MemoryStream(cipher))
                    {
                        using (var csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
                        {
                            using (var srDecrypt = new StreamReader(csDecrypt))
                            {
                                result = srDecrypt.ReadToEnd();
                            }
                        }
                    }
                    return result;
                }
            }
        }
    }
}