Google TOTP Two-factor Authentication(两次验证密码) for PHP

谷歌在今年年初公布的2因子认证(2FA)的G-邮件提供了一个为Android,iPhone和黑莓的应用程序名为Google的Authenticator生成一个时间登录令牌。 这篇文章将展示如何实现谷歌2FA Web应用程序,以防止被盗的凭据。

谷歌验证器是基于RFC 4226 -基于时间的一次性密码(TOTP)这是使用16位基32( RFC 4648 )编码的种子值初始化。 TOTP使用的初始种子可以进入谷歌通过使用QR码相机或通过键盘的Authenticator。 谷歌还提供了一个PAM模块,允许用户集成的sshd 2FA。

可以写一个模块,以支持在任何语言的Google TOTP - 写PHP库唯一需要注意的是缺乏一个RFC 4648兼容的基地32解码功能。 32基本功能是需要解码的初始种子。 这可能是最棘手的部分实施谷歌的2FA。 可以使用以下功能:

<?php
function base32_decode($b32) {
  $lut = array("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
  );

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

  for ($i = 0; $i < $l; $i++) {

       $n = $n << 5;
       $n = $n + $lut[$b32[$i]];
       $j = $j + 5;

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

  return $binary;
}
?>

这个二进制的数据值将被用来生成一个时间标记,以及当前的Unix时间戳在一个SHA1哈希。除以30,口令每30秒改变的Unix时间戳记(基于计数器的当然就是一次换一个啦)。

<?php
function get_timestamp() {
   return floor(microtime(true)/30);
}
?>

但是不能只是直入SHA1功能从get_timestamp传递的数量,首先需要的时间戳记将减少到8个字节的二进制字符串,由于数据包不支持64位的整数,我们用两个32位无符号整数,以弥补二进制形式。

<?php
$binary_timestamp = pack('N*', 0) . pack('N*', $timestamp);
?>

一旦你有二进制的seed和你有二进制时间戳传递到他们的“hash_mhac”功能。这给你一个20字节的SHA1字符串。

<?php
$hash = hash_hmac ('sha1', $binary_timestamp, $binary_key, true);
?>

进行哈希处理根据RFC4226获得一次性密码。

<?php
$offset = ord($hash[19]) & 0xf;

$OTP = (
   ((ord($hash[$offset+0]) & 0x7f) << 24 ) |
    ((ord($hash[$offset+1]) & 0xff) << 16 ) |
    ((ord($hash[$offset+2]) & 0xff) << 8 ) |
    (ord($hash[$offset+3]) & 0xff)
   ) % pow(10, 6);

?>

现在TOTP应该包含您的一次性密码。但是仍然有些小问题,如果你想使用这个应用程序,可能有以下的小问题:

您的客户端和服务器的时钟可能不同步 - 这可能意味着,当你来检查您的令牌生成的用户,它会失败。这是你可以规定,客户端和服务器的时钟必须是在完美的同步,或者你需要创建一个函数,检查对那些令牌+ / - 当前服务器时间2分钟。这将允许您的客户端和服务器出长达2分钟,但显然增加了机会,使攻击者能够正确猜测一个时间令牌。

如果没有次数上限,用户可以在猜测令牌,它可能会以蛮力一次性令牌。

如果seed太小了,攻击者可以拦截一些令牌,它可能会蛮力的种子值,允许攻击者产生新的一次性令牌。出于这个原因,谷歌执行最低的16个字符或80位的种子长度。

如果令牌没有标记为无效,因为它已被用于尽快截获令牌的攻击者可能能够快速重新获得。

Google Authenticator: Seed value 'PEHMPSDNLXIOG65U'

在这里有一个PHP类,实现谷歌TOTP。针对蛮力攻击其失踪的保护,但其他功能齐全。

<?php
<?
/**
 * 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
 **/

class Google2FA {

    const keyRegeneration   = 30;   // Interval between key regeneration
    const otpLength     = 6;    // Length of the Token generated

    private static $lut = array(    // 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
     * @return string
     **/
    public static function generate_secret_key($length = 16) {
        $b32    = "234567QWERTYUIOPASDFGHJKLZXCVBNM";
        $s  = "";

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

        return $s;
    }

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

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

        return $binary;
    }

    /**
     * Takes the secret key and the timestamp and returns the one time
     * password.
     *
     * @param binary $key - Secret key in binary form.
     * @param integer $counter - Timestamp as returned by get_timestamp.
     * @return string
     **/
    public static function oath_hotp($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);
    }

    /**
     * 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 $useTimeStamp
     * @return boolean
     **/
    public static function verify_key($b32seed, $key, $window = 4, $useTimeStamp = true) {

        $timeStamp = self::get_timestamp();

        if ($useTimeStamp !== true) $timeStamp = (int)$useTimeStamp;

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

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

        return false;

    }

    /**
     * Extracts the OTP from the SHA1 hash.
     * @param binary $hash
     * @return integer
     **/
    public static function oath_truncate($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);
    }

}

$InitalizationKey = "PEHMPSDNLXIOG65U";                   // Set the inital key

$TimeStamp    = Google2FA::get_timestamp();
$secretkey    = Google2FA::base32_decode($InitalizationKey);    // Decode it into binary
$otp          = Google2FA::oath_hotp($secretkey, $TimeStamp);   // Get current token

echo("Init key: $InitalizationKey\n");
echo("Timestamp: $TimeStamp\n");
echo("One time password: $otp\n");

// Use this to verify a key as it allows for some time drift.

$result = Google2FA::verify_key($InitalizationKey, "123456");

var_dump($result);
?>

你可以检查其工作由安装谷歌的Authenticator应用QR码和扫描的权利 - 由应用程序生成的代码应匹配类生成的代码。

这个function Google2FA::verify_key 应该用来验证用户一次令牌,因为它允许客户端时钟漂移2分钟服务器时间两侧。

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