Gazelle/classes/twofa.class.php

<?php
#declare(strict_types=1);

class TwoFactorAuth
{
    private $algorithm;
    private $period;
    private $digits;
    private $issuer;
    private static $_base32dict = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567=';
    private static $_base32;
    private static $_base32lookup = [];
    private static $_supportedalgos = array('sha1', 'sha256', 'sha512', 'md5');

    public function __construct($issuer = null, $digits = 6, $period = 30, $algorithm = 'sha1')
    {
        $this->issuer = $issuer;
        $this->digits = $digits;
        $this->period = $period;

        $algorithm = strtolower(trim($algorithm));
        if (!in_array($algorithm, self::$_supportedalgos)) {
            $algorithm = 'sha1';
        }
        $this->algorithm = $algorithm;

        self::$_base32 = str_split(self::$_base32dict);
        self::$_base32lookup = array_flip(self::$_base32);
    }

    public function createSecret($bits = 210)
    {
        $secret = '';
        $bytes = ceil($bits / 5); //We use 5 bits of each byte (since we have a 32-character 'alphabet' / BASE32)
        $rnd = random_bytes($bytes);

        for ($i = 0; $i < $bytes; $i++) {
            $secret .= self::$_base32[ord($rnd[$i]) & 31]; //Mask out left 3 bits for 0-31 values
        }
        return $secret;
    }

    // Calculate the code with given secret and point in time
    public function getCode($secret, $time = null)
    {
        $secretkey = $this->base32Decode($secret);

        $timestamp = "\0\0\0\0" . pack('N*', $this->getTimeSlice($this->getTime($time)));  // Pack time into binary string
        $hashhmac = hash_hmac($this->algorithm, $timestamp, $secretkey, true);             // Hash it with users secret key
        $hashpart = substr($hashhmac, ord(substr($hashhmac, -1)) & 0x0F, 4);               // Use last nibble of result as index/offset and grab 4 bytes of the result
        $value = unpack('N', $hashpart);                                                   // Unpack binary value
        $value = $value[1] & 0x7FFFFFFF;                                                   // Drop MSB, keep only 31 bits

        return str_pad($value % pow(10, $this->digits), $this->digits, '0', STR_PAD_LEFT);
    }

    // Check if the code is correct. This will accept codes starting from now +/- ($discrepancy * period) seconds
    public function verifyCode($secret, $code, $discrepancy = 1, $time = null)
    {
        $result = false;
        $timetamp = $this->getTime($time);

        // Always iterate all possible codes to prevent timing-attacks
        for ($i = -$discrepancy; $i <= $discrepancy; $i++) {
            $result |= hash_equals($this->getCode($secret, $timetamp + ($i * $this->period)), $code);
        }

        return (bool)$result;
    }

    // Get data-uri of QRCode
    public function getQRCodeImageAsDataUri($label, $secret, $size = 300)
    {
        if (exec('which qrencode')) {
            $QRCodeImage = shell_exec("qrencode -s ".(int)($size/40)." -m 3 -o - '".$this->getQRText($label, $secret)."'");
        } else {
            $curlhandle = curl_init();

            curl_setopt_array($curlhandle, array(
            CURLOPT_URL => 'https://chart.googleapis.com/chart?cht=qr&chs='.$size.'x'.$size.'&chld=L|1&chl='.rawurlencode($this->getQRText($label, $secret)),
            CURLOPT_RETURNTRANSFER => true,
            CURLOPT_CONNECTTIMEOUT => 10,
            CURLOPT_DNS_CACHE_TIMEOUT => 10,
            CURLOPT_TIMEOUT => 10,
            CURLOPT_SSL_VERIFYPEER => false,
            CURLOPT_USERAGENT => 'TwoFactorAuth'
            ));

            $QRCodeImage = curl_exec($curlhandle);
            curl_close($curlhandle);
        }
        return 'data:image/png;base64,'.base64_encode($QRCodeImage);
    }

    private function getTime($time)
    {
        return ($time === null) ? time() : $time;
    }

    private function getTimeSlice($time = null, $offset = 0)
    {
        return (int)floor($time / $this->period) + ($offset * $this->period);
    }

    // Builds a string to be encoded in a QR code
    public function getQRText($label, $secret)
    {
        $QRText = 'otpauth://totp/'.rawurlencode($label).'?secret='.rawurlencode($secret);
        $QRText .= ($this->issuer) ? '&issuer='.rawurlencode($this->issuer) : '';
        $QRText .= ($this->period != 30) ? '&period='.intval($this->period) : '';
        $QRText .= ($this->algorithm != 'sha1') ? '&algorithm='.rawurlencode(strtoupper($this->algorithm)) : '';
        $QRText .= ($this->digits != 6) ? '&digits='.intval($this->digits) : '';
        return $QRText;
    }

    private function base32Decode($value)
    {
        if (strlen($value)==0) {
            return '';
        }

        $buffer = '';
        foreach (str_split($value) as $char) {
            if ($char !== '=') {
                $buffer .= str_pad(decbin(self::$_base32lookup[$char]), 5, 0, STR_PAD_LEFT);
            }
        }
        
        $length = strlen($buffer);
        $blocks = trim(chunk_split(substr($buffer, 0, $length - ($length % 8)), 8, ' '));

        $output = '';
        foreach (explode(' ', $blocks) as $block) {
            $output .= chr(bindec(str_pad($block, 8, 0, STR_PAD_RIGHT)));
        }

        return $output;
    }
}