I have a  login and sign-up form and use the encrypt library to encrypt the password. login and sign up form and use the encrypt library to encrypt the password. 
Code to encrypt the password:
$this->encrypt->encode('my password'); 
Add encrypt library
 $autoload['libraries'] = array('encrypt');
Setting the secret key in config:
$config['encryption_key'] = 'nmsc encrypt secret key';
 when I try to upload it to my website to the ubuntu server I've got an error that says
The Encrypt library requires the Mcrypt extension
How can I fix this?