像google一样加一个两步密码验证

 

google的两步密码验证出来已经相当一段时间了，相信很多同学都用过，其工作原理是:

两步验证为您的 Google 帐户多加了一道安全防线

除了用户名和密码外，您还需要输入登录时 Google 通过短信或语音留言向您发送的验证码。

实际上这个东西就是类似网银口令卡的东西，但是这个实现起来更为简单，你在google账户开启了两步密码验证以后，你先得正确输入了密码，再拿出手机，查出当前的第二步密码，正确输入后才能访问你的账户，这个密码每30秒就过期并且会生成一个新密码，对了，这个东西叫做google authenticator,google是把他开源出来了的，并且有了IOS客户端，Android客户端，Blackberry客户端，甚至有Nokia客户端（这个非官方出品），有算法用啥语言来实现，实际上已经不重要了！因此，用PHP来实现google authenticator算法根本不是问题,请看老外的代码 。

对！我们有了这些资源，就可以实现自己的两步密码验证了，实际上这个算法是一个叫做HOTP的东西，算法的核心根据密钥和时间戳或者计数器来算出一个一次性密码，像google authenticator是30秒一换（基于计数器的当然就是一次换一个啦），密钥只有google authenticator和服务器知道，暴露出来的仅仅是一个每30秒（或每次）换一次的token，也就是一次性密码。

 

截图是通过二维码扫描进手机的，生成二维码直接用的google charts里的qr code生成工具，这个很好用的啦！个人觉着比直接PHP gd去画来的方便啊。

这里附上一个小小的基于时间的demo，点进去玩玩（我发现时间过期很不准确，待日后再改）。

<?
/**
 * 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);