Crypto.php

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<?php

namespace Elgg\Security;

use Elgg\Exceptions\RangeException;

class Crypto {

    const CHARS_PASSWORD = 'bcdfghjklmnpqrstvwxyz2346789';

    const CHARS_HEX = '0123456789abcdef';

    public function getRandomString($length, $chars = null) {
        if ($length < 1) {
            throw new RangeException('Length should be >= 1');
        }

        if (empty($chars)) {
            $numBytes = ceil($length * 0.75);
            $bytes = random_bytes($numBytes);
            $string = substr(rtrim(base64_encode($bytes), '='), 0, $length);

            // Base64 URL
            return strtr($string, '+/', '-_');
        }

        if ($chars == self::CHARS_HEX) {
            // hex is easy
            $bytes = random_bytes(ceil($length / 2));
            return substr(bin2hex($bytes), 0, $length);
        }

        $listLen = strlen($chars);

        if ($listLen == 1) {
            return str_repeat($chars, $length);
        }

        $bytes  = random_bytes($length);
        $pos    = 0;
        $result = '';
        for ($i = 0; $i < $length; $i++) {
            $pos     = ($pos + ord($bytes[$i])) % $listLen;
            $result .= $chars[$pos];
        }

        return $result;
    }

    public function areEqual($str1, $str2) {
        $len1 = $this->strlen($str1);
        $len2 = $this->strlen($str2);
        if ($len1 !== $len2) {
            return false;
        }

        $status = 0;
        for ($i = 0; $i < $len1; $i++) {
            $status |= (ord($str1[$i]) ^ ord($str2[$i]));
        }

        return $status === 0;
    }

    protected function strlen($binary_string) {
        if (function_exists('mb_strlen')) {
            return mb_strlen($binary_string, '8bit');
        }
        
        return strlen($binary_string);
    }
}