调用未定义方法CI_Encrypt::sha1()

我从youtube教程codeigniter -插入但是，当我使用codeigniter 2的加密库时，我在浏览器的控制器文件中得到这个错误。
使用加密时出现错误代码。

$paramUsu['clave'] = $this->encrypt->sha1($this->input->post('txtClave'));

但是当我不加加密地传递它时，它工作得很好

$paramUsu['clave'] = $this->input->post('txtClave');

我的浏览器出现了这个错误:

致命错误:调用未定义的方法CI_Encrypt::sha1()在C:'xampp'htdocs'TRAINING'tutorialCI'application'controllers'cpersona.php第31行
遇到PHP错误严重性:错误消息:调用未定义方法CI_Encrypt::sha1()
文件名:控制器/cpersona.php
行号:31
回溯:

<?php
defined('BASEPATH') OR exit('No direct script access allowed');
class Cpersona extends CI_Controller {
    function __construct()
    {
        parent::__construct();
                //call model
                $this->load->model('mpersona');
                $this->load->model('musuario');
                //call encryption library for password at 'clave' textfield
                $this->load->library('encrypt');
    }
    public function index(){
        $this->load->view('persona/vpersona');
    }
    public function guardar(){
        //persona
        $param['dni'] = $this->input->post('txtDNI');
        $param['nombre'] = $this->input->post('txtNombre');
        $param['appaterno'] = $this->input->post('txtApPaterno');
        $param['apmaterno'] = $this->input->post('txtApMaterno');
        $param['email'] = $this->input->post('txtEmail');
        $param['fecnac'] = $this->input->post('datFecNac');
        //usuario
        $paramUsu['nomUsuario'] = $this->input->post('txtUsuario');
        //$paramUsu['clave'] = $this->input->post('txtClave');
        $paramUsu['clave'] = $this->encrypt->sha1($this->input->post('txtClave'));
        //call function name in model
        //call function variable '$param'
        //$this->mpersona->guardar($param);
        $lastId = $this->mpersona->guardar($param);
        //check if $lastId is filled in persona table
        if ($lastId > 0){
            $paramUsu['idPersona'] = $lastId;
            //$paramUsu value will be go also in usuario model
            $this->musuario->guardarUsuario($paramUsu);
        }
    }
}