Find High Entropy Strings in Web Pages

Entropy.php

<?php

class Entropy {    
    protected $minEntropy = 30;
    protected $minStrLength = 12;
    protected $found = [];
    protected $chars = [];
    protected $fileContents = [];
    protected $plusWeight = 5;
    protected $prevChar = 5;
    protected $prevGroup = 2;

    public function __construct($minEntropy = 30, $minStrLength = 12) {
        $this->minEntropy = $minEntropy;
        $this->minStrLength = $minStrLength;

        $upperChars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
        $lowerChars = 'abcdefghijklmnopqrstuvwxyz';
        $digits = '0123456789';
        $special = '!"£$%^&*()_+-={}[]:@~;\'#<>,.?|\\';
        $hex = 'ABCDEF0123456789abcdef';

        $this->chars['upper'] = str_split($upperChars);
        $this->chars['lower'] = str_split($lowerChars);
        $this->chars['digits'] = str_split($digits);
        $this->chars['special'] = str_split($special);
        $this->chars['hex'] = str_split($hex);

        return $this;
    }

    public function loadFile($file) {
        if(strtolower(substr($file, 0, 4)) === 'http') {
            $ch = curl_init();
            curl_setopt($ch, CURLOPT_URL, $file);
            curl_setopt($ch, CURLOPT_FOLLOWLOCATION, $file);
            curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
            $data = curl_exec($ch);

            $this->fileContents[] = $data;
            
        } else {
            $this->fileContents[] = file_get_contents($file);
        }

        return $this;
    }

    public function findEntropy() {
        $final = [];
        if(!empty($this->fileContents)) {
            foreach($this->fileContents as $data) {
                $matches = [];
                preg_match_all('/([a-zA-Z0-9=._+-\/]{'.$this->minStrLength.',})/i', $data, $matches);
                if(!empty($matches)) {
                    foreach($matches[0] as $match) {
                        $entropy = 0;
                        $charEntropyArr = str_split($match);
                        foreach($charEntropyArr as $key => $char) {
                            $idx = ($key == 0 ? 0 : $key - 1);
                            $prev = $charEntropyArr[$idx];
                            foreach($this->chars as $key => $charGroup) {
                                if(in_array($char, $this->chars[$key])) {
                                    $entropy += $this->plusWeight;

                                    // Check if it was in the same as the previous character's group
                                    if(!in_array($prev, $this->chars[$key])) {
                                        if($prev == $char) {
                                            $entropy -= $this->prevChar;
                                        } else {
                                            $entropy -= $this->prevGroup;
                                        }
                                    }
                                }
                            }
                        }
                        $this->found[] = ['string' => $match, 'entropy' => $entropy];
                    }   
                }
            }
        }
        $return = [];
        if(!empty($this->found)) {
            foreach($this->found as $found) {
                if($found['entropy'] >= $this->minEntropy) {
                    $return[] = $found;
                }
            }
        }
        return $return;
    }
}
$entropy = new Entropy(220, 20);
$found = $entropy->loadFile('http://writing-backend.playground.easybib.com/config')->findEntropy();
foreach($found as $f) {
    printf("%s has the entropy of %d\n", $f['string'], $f['entropy']);
}