How to fix Codeigniter error (PHP 7.2) - the Encrypt library requires the Mcrypt extension

I get this error when using encrypt library in codeigniter 3:
the Encrypt library requires the Mcrypt extension

when i try to install mcrypt plugin:
sudo apt-get install php7.2-mcrypt

i got this error:
Unable to locate package php7.2-mcrypt

This video will help you how to fix that error