<?php
/**
 * sysPass
 *
 * @author nuxsmin
 * @link http://syspass.org
 * @copyright 2012-2017, Rubén Domínguez nuxsmin@$syspass.org
 *
 * This file is part of sysPass.
 *
 * sysPass is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * sysPass is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 *  along with sysPass.  If not, see <http://www.gnu.org/licenses/>.
 */

/**
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * PHP Google two-factor authentication module.
 *
 * See http://www.idontplaydarts.com/2011/07/google-totp-two-factor-authentication-for-php/
 * for more details
 *
 * @author Phil
 **/

namespace Plugins\Authenticator;

/**
 * Class Google2FA
 *
 * @package SP\Auth
 */
class Google2FA
{
    /**
     * Interval between key regeneration
     */
    const keyRegeneration = 30;
    /**
     * Length of the Token generated
     */
    const otpLength = 6;

    /**
     * Lookup needed for Base32 encoding
     *
     * @var array
     */
    private static $lut = [    // Lookup needed for Base32 encoding
        'A' => 0, 'B' => 1,
        'C' => 2, 'D' => 3,
        'E' => 4, 'F' => 5,
        'G' => 6, 'H' => 7,
        'I' => 8, 'J' => 9,
        'K' => 10, 'L' => 11,
        'M' => 12, 'N' => 13,
        'O' => 14, 'P' => 15,
        'Q' => 16, 'R' => 17,
        'S' => 18, 'T' => 19,
        'U' => 20, 'V' => 21,
        'W' => 22, 'X' => 23,
        'Y' => 24, 'Z' => 25,
        '2' => 26, '3' => 27,
        '4' => 28, '5' => 29,
        '6' => 30, '7' => 31
    ];

    /**
     * Generates a 16 digit secret key in base32 format
     *
     * @param int $length
     * @return string
     */
    public static function generate_secret_key($length = 16)
    {
        $b32 = '234567QWERTYUIOPASDFGHJKLZXCVBNM';
        $s = '';

        for ($i = 0; $i < $length; $i++) {
            $s .= $b32[mt_rand(0, 31)];
        }

        return $s;
    }

    /**
     * Verifys a user inputted key against the current timestamp. Checks $window
     * keys either side of the timestamp.
     *
     * @param string  $b32seed
     * @param string  $key - User specified key
     * @param integer $window
     * @param boolean $useTimeStamp
     * @return boolean
     * @throws \Exception
     **/
    public static function verify_key($b32seed, $key, $window = 4, $useTimeStamp = true)
    {

        $timeStamp = ($useTimeStamp !== true) ? (int)$useTimeStamp : self::get_timestamp();

        $binarySeed = self::base32_decode($b32seed);

        for ($ts = $timeStamp - $window; $ts <= $timeStamp + $window; $ts++) {
            if (self::oath_totp($binarySeed, $ts) == $key) {
                return true;
            }
        }

        return false;

    }

    /**
     * Returns the current Unix Timestamp devided by the keyRegeneration
     * period.
     *
     * @return integer
     **/
    public static function get_timestamp()
    {
        return floor(microtime(true) / self::keyRegeneration);
    }

    /**
     * Decodes a base32 string into a binary string.
     **/
    public static function base32_decode($b32)
    {

        $b32 = strtoupper($b32);

        if (!preg_match('/^[ABCDEFGHIJKLMNOPQRSTUVWXYZ234567]+$/', $b32, $match)) {
            throw new \Exception('Invalid characters in the base32 string.');
        }

        $l = strlen($b32);
        $n = 0;
        $j = 0;
        $binary = '';

        for ($i = 0; $i < $l; $i++) {
            $n <<= 5; // Move buffer left by 5 to make room
            $n += self::$lut[$b32[$i]]; // Add value into buffer
            $j += 5; // Keep track of number of bits in buffer

            if ($j >= 8) {
                $j -= 8;
                $binary .= chr(($n & (0xFF << $j)) >> $j);
            }
        }

        return $binary;
    }

    /**
     * Takes the secret key and the timestamp and returns the one time
     * password.
     *
     * @param string $key     - Secret key in binary form.
     * @param int    $counter - Timestamp as returned by get_timestamp.
     * @return string
     * @throws \Exception
     */
    public static function oath_totp($key, $counter)
    {
        if (strlen($key) < 8) {
            throw new \Exception('Secret key is too short. Must be at least 16 base 32 characters');
        }

        $bin_counter = pack('N*', 0) . pack('N*', $counter); // Counter must be 64-bit int
        $hash = hash_hmac('sha1', $bin_counter, $key, true);

        return str_pad(self::oath_truncate($hash), self::otpLength, '0', STR_PAD_LEFT);
    }

    /**
     * Extracts the OTP from the SHA1 hash.
     *
     * @param string $hash
     * @return integer
     **/
    public static function oath_truncate($hash)
    {
        $offset = ord($hash[19]) & 0xf;

        return (
                ((ord($hash[$offset + 0]) & 0x7f) << 24) |
                ((ord($hash[$offset + 1]) & 0xff) << 16) |
                ((ord($hash[$offset + 2]) & 0xff) << 8) |
                (ord($hash[$offset + 3]) & 0xff)
            ) % pow(10, self::otpLength);
    }
}