gistfile1.cs

        private static readonly byte[] LastLoginSalt = new byte[] { 0x0c, 0x9d, 0x4a, 0xe4, 0x1e, 0x83, 0x15, 0xfc };
        private const string LastLoginPassword = "passwordfile";
        public static LastLogin DecryptLastLogin()
        {
            byte[] encryptedLogin = File.ReadAllBytes(Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), ".minecraft", "lastlogin"));
            PKCSKeyGenerator crypto = new PKCSKeyGenerator(LastLoginPassword, LastLoginSalt, 5, 1); // https://gist.github.com/bef81cd0bd456314f4d0
            ICryptoTransform cryptoTransform = crypto.Decryptor;
            byte[] decrypted = cryptoTransform.TransformFinalBlock(encryptedLogin, 0, encryptedLogin.Length);
            short userLength = IPAddress.HostToNetworkOrder(BitConverter.ToInt16(decrypted, 0));
            byte[] user = decrypted.Skip(2).Take(userLength).ToArray();
            short passLength = IPAddress.HostToNetworkOrder(BitConverter.ToInt16(decrypted, userLength + 2));
            byte[] password = decrypted.Skip(4 + userLength).ToArray();
            LastLogin result = new LastLogin();
            result.Username = Encoding.UTF8.GetString(user);
            result.Password = Encoding.UTF8.GetString(password);
            return result;
        }

        public class LastLogin
        {
            public string Username { get; set; }
            public string Password { get; set; }
        }