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。