Simple password validator for PHP using mb_ereg_match()

phpmberegpasswd.php

<?php
/*
 * Simple password construct validator for PHP
 * This code uses mb_ereg_match()
 * Joaquim Homrighausen <joho@webbplatsen.se>
 * Mar 19, 2024
 *
 * Do whatever you want with this snippet :)
 *
 * This may not necessarily agree with the section "Strength of Memorized
 * Secrets" in the document from NIST:
 *
 * NIST Special Publication 800-63B
 * Digital Identity Guidelines
 * Authentication and Lifecycle Management
 * https://pages.nist.gov/800-63-3/sp800-63b.html
 */


/*
 * Requires that password is at least $min_length characters long (default 8).
 * Requires that password contains at least one UPPERCASE character.
 * Requires that password contains at least one lowercase character.
 * Requires that password contains at least one digit.
 * Requires that password contains at least one of the following:
 *   ^ ! @ # $ % & * _ - \ / { } [ ] .
 */

function password_mb_ereg_test( $password_string, $min_length = 8 ) {
    if ($min_length < 8) {
        // We want at least eight characters, but probably 64 ;-)
        $min_length = 8;
    }                                   
    $match_rules = '^(?=.+[\.\^\!\@\#\$\%\^\&\*\-\_\\\/\[\]\{\}])(?=.+[[:digit:]])(?=.+[[:upper:]])(?=.+[[:lower:]]).{' . (int)$min_length . ',}$';
    return ( mb_ereg_match( $match_rules, $password_string ) );
}