hash_hmac() undefined function error on new install

This is a completely new install, and I'm getting:

Fatal error: Call to undefined function hash_hmac() in Session.php on line 677.

I even downloaded Codeigniter and unzipped it again, just to be sure.  I got the Welcome page, and made these changes:

1.  Added a Constructor to the Welcome page, with the $this->load->library('session') included:

public function __construct()
 {
     
parent::__construct();
           
$this->load->library('session');
     
}

2.  Added an encryption key in config.php:

$config['encryption_key'] = 'asdfasfd';

That's it!  Generates the error.

mcrypt is enables per phpinfo.

No doubt I'm missing something, but I can't spot it.  

Any suggestions?

TIA

John