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<?php
/**
* CPasswordHelper class file.
*
* @author Tom Worster <fsb@thefsb.org>
* @link http://www.yiiframework.com/
* @copyright 2008-2013 Yii Software LLC
* @license http://www.yiiframework.com/license/
*/
/**
* CPasswordHelper provides a simple API for secure password hashing and verification.
*
* CPasswordHelper uses the Blowfish hash algorithm available in many PHP runtime
* environments through the PHP {@link http://php.net/manual/en/function.crypt.php crypt()}
* built-in function. As of Dec 2012 it is the strongest algorithm available in PHP
* and the only algorithm without some security concerns surrounding it. For this reason,
* CPasswordHelper fails when run in an environment that does not have
* crypt() with its Blowfish option and $2y hash fix. Compatible system is:
*
* (1) Most *nix systems since PHP 4 (the algorithm is part of the library function crypt(3));
* (2) Any PHP since 5.3.7 or PHP with the {@link http://www.hardened-php.net/suhosin/ Suhosin patch} including
* $2y fix backported. Note that Debian's 5.3.3 is not supported.
*
* For more information about password hashing, crypt() and Blowfish, please read
* the Yii Wiki article
* {@link http://www.yiiframework.com/wiki/425/use-crypt-for-password-storage/ Use crypt() for password storage}.
* and the
* PHP RFC {@link http://wiki.php.net/rfc/password_hash Adding simple password hashing API}.
*
* CPasswordHelper throws an exception if the Blowfish hash algorithm is not
* available in the runtime PHP's crypt() function. It can be used as follows
*
* Generate a hash from a password:
* <pre>
* $hash = CPasswordHelper::hashPassword($password);
* </pre>
* This hash can be stored in a database (e.g. CHAR(60) CHARACTER SET latin1). The
* hash is usually generated and saved to the database when the user enters a new password.
* But it can also be useful to generate and save a hash after validating a user's
* password in order to change the cost or refresh the salt.
*
* To verify a password, fetch the user's saved hash from the database (into $hash) and:
* <pre>
* if (CPasswordHelper::verifyPassword($password, $hash))
* // password is good
* else
* // password is bad
* </pre>
*
* @author Tom Worster <fsb@thefsb.org>
* @package system.utils
* @since 1.1.14
*/
class CPasswordHelper
{
/**
* Check for availability of PHP crypt() with the Blowfish hash option.
* @throws CException if the runtime system does not have PHP crypt() or its Blowfish hash option.
*/
protected static function checkBlowfish()
{
if(!function_exists('crypt'))
throw new CException(Yii::t('yii','{class} requires the PHP crypt() function. This system does not have it.',
array('{class}'=>__CLASS__)));
if(!defined('CRYPT_BLOWFISH') || !CRYPT_BLOWFISH)
throw new CException(Yii::t('yii',
'{class} requires the Blowfish option of the PHP crypt() function. This system does not have it.',
array('{class}'=>__CLASS__)));
}
/**
* Generate a secure hash from a password and a random salt.
*
* Uses the
* PHP {@link http://php.net/manual/en/function.crypt.php crypt()} built-in function
* with the Blowfish hash option.
*
* @param string $password The password to be hashed.
* @param int $cost Cost parameter used by the Blowfish hash algorithm.
* The higher the value of cost,
* the longer it takes to generate the hash and to verify a password against it. Higher cost
* therefore slows down a brute-force attack. For best protection against brute for attacks,
* set it to the highest value that is tolerable on production servers. The time taken to
* compute the hash doubles for every increment by one of $cost. So, for example, if the
* hash takes 1 second to compute when $cost is 14 then then the compute time varies as
* 2^($cost - 14) seconds.
* @return string The password hash string, always 60 ASCII characters.
* @throws CException on bad password parameter or if crypt() with Blowfish hash is not available.
*/
public static function hashPassword($password,$cost=13)
{
self::checkBlowfish();
$salt=self::generateSalt($cost);
$hash=crypt($password,$salt);
if(!is_string($hash) || (function_exists('mb_strlen') ? mb_strlen($hash, '8bit') : strlen($hash))<32)
throw new CException(Yii::t('yii','Internal error while generating hash.'));
return $hash;
}
/**
* Verify a password against a hash.
*
* @param string $password The password to verify. If password is empty or not a string, method will return false.
* @param string $hash The hash to verify the password against.
* @return bool True if the password matches the hash.
* @throws CException on bad password or hash parameters or if crypt() with Blowfish hash is not available.
*/
public static function verifyPassword($password, $hash)
{
self::checkBlowfish();
if(!is_string($password) || $password==='')
return false;
if (!$password || !preg_match('{^\$2[axy]\$(\d\d)\$[\./0-9A-Za-z]{22}}',$hash,$matches) ||
$matches[1]<4 || $matches[1]>31)
return false;
$test=crypt($password,$hash);
if(!is_string($test) || strlen($test)<32)
return false;
return self::same($test, $hash);
}
/**
* Check for sameness of two strings using an algorithm with timing
* independent of the string values if the subject strings are of equal length.
*
* The function can be useful to prevent timing attacks. For example, if $a and $b
* are both hash values from the same algorithm, then the timing of this function
* does not reveal whether or not there is a match.
*
* NOTE: timing is affected if $a and $b are different lengths or either is not a
* string. For the purpose of checking password hash this does not reveal information
* useful to an attacker.
*
* @see http://blog.astrumfutura.com/2010/10/nanosecond-scale-remote-timing-attacks-on-php-applications-time-to-take-them-seriously/
* @see http://codereview.stackexchange.com/questions/13512
* @see https://github.com/ircmaxell/password_compat/blob/master/lib/password.php
*
* @param string $a First subject string to compare.
* @param string $b Second subject string to compare.
* @return bool true if the strings are the same, false if they are different or if
* either is not a string.
*/
public static function same($a,$b)
{
if(!is_string($a) || !is_string($b))
return false;
$mb=function_exists('mb_strlen');
$length=$mb ? mb_strlen($a,'8bit') : strlen($a);
if($length!==($mb ? mb_strlen($b,'8bit') : strlen($b)))
return false;
$check=0;
for($i=0;$i<$length;$i+=1)
$check|=(ord($a[$i])^ord($b[$i]));
return $check===0;
}
/**
* Generates a salt that can be used to generate a password hash.
*
* The PHP {@link http://php.net/manual/en/function.crypt.php crypt()} built-in function
* requires, for the Blowfish hash algorithm, a salt string in a specific format:
* "$2y$" (in which the "y" may be replaced by "a" or "y" see PHP manual for details),
* a two digit cost parameter,
* "$",
* 22 characters from the alphabet "./0-9A-Za-z".
*
* @param int $cost Cost parameter used by the Blowfish hash algorithm.
* @return string the random salt value.
* @throws CException in case of invalid cost number
*/
public static function generateSalt($cost=13)
{
if(!is_numeric($cost))
throw new CException(Yii::t('yii','{class}::$cost must be a number.',array('{class}'=>__CLASS__)));
$cost=(int)$cost;
if($cost<4 || $cost>31)
throw new CException(Yii::t('yii','{class}::$cost must be between 4 and 31.',array('{class}'=>__CLASS__)));
if(($random=Yii::app()->getSecurityManager()->generateRandomString(22,true))===false)
if(($random=Yii::app()->getSecurityManager()->generateRandomString(22,false))===false)
throw new CException(Yii::t('yii','Unable to generate random string.'));
return sprintf('$2y$%02d$',$cost).strtr($random,array('_'=>'.','~'=>'/'));
}
}
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