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Use crypt() for password storage
Revision #10 has been created by samdark on Mar 29, 2013, 10:20:24 AM with the memo:
trying to fix github link
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Title unchanged
Use crypt() for password storage
Category unchanged
Tutorials
Yii version unchanged
Tags unchanged
Authentication, security, password, hash, hashing
Content changed
Storing passwords in web apps
----
> There is now a `CPasswordHelper` class in `system.utils` <a href="https://github.com/yiisoft/yii/blob/master/framework/utils/CPasswordHelper.php">at GitHub</a>
> that provides an API to simplify the use of `crypt()` for password storage.
> While this wiki article remains valid, it will in due course be rewritten
> to refer to the new class as well as explain how it works.
There are many tutorials and examples that show storage of passwords in a table.
Often the methods used are substandard and very easy to crack. There are many web pages and tutorials that show how to do it wrong.
crypt('EgzamplPassword', '$2a$10$1qAz2wSx3eDc4rFv5tGb5t')
>> '$2a$10$1qAz2wSx3eDc4rFv5tGb5e4jVuld5/KF2Kpy.B8D2XoC031sReFGi'
```
crypt('EgzamplPassword', '$2a$10$1qAz2wSx3eDc4rFv5tGb5t12345678901234567890')
>> '$2a$10$1qAz2wSx3eDc4rFv5tGb5e4jVuld5/KF2Kpy.B8D2XoC031sReFGi'
crypt('EgzamplPassword', '$2a$10$1qAz2wSx3eDc4rFv5tGb5t$2a$10$1qAz2wSx3eDc4rFv5tGb5t')
>> '$2a$10$1qAz2wSx3eDc4rFv5tGb5e4jVuld5/KF2Kpy.B8D2XoC031sReFGi'
```
crypt('EgzamplPassword', '$2a$10$1qAz2wSx3eDc4rFv5tGb5e4jVuld5/KF2Kpy.B8D2XoC031sReFGi')
>> '$2a$10$1qAz2wSx3eDc4rFv5tGb5e4jVuld5/KF2Kpy.B8D2XoC031sReFGi'
```
```php
$hash === crypt($password, $hash)
```Compare the strings `$hash` and `crypt($password, $hash)`.
**NOTE:** We should use a constant-time string comparison algorithm to defeat
the possibility of
[timing attacks](http://blog.astrumfutura.com/2010/10/nanosecond-scale-remote-timing-attacks-on-php-applications-time-to-take-them-seriously/)
learning the result of validation. See below for an example.
$rand = array();
for ($i = 0; $i < 8;++$i += 1) {
$rand[] = pack('S', mt_rand(0, 0xffff));
}
create table user (
id int not null auto_increment primary key,
username varchar(255) not null,
password_hash char(64) not null,
unique key (email)
)
~~~
if ($password_hash === crypt($form->password, $record->passwordHash))
// password is correct
else
// password is wrong
```
## Constant-time string comparison.
This function is based on
[this](http://codereview.stackexchange.com/questions/13512/constant-time-string-comparision-in-php-to-prevent-timing-attacks)
and
[this](https://github.com/ircmaxell/password_compat/blob/master/lib/password.php).
```php
function same($a, $b) {
/**
* @see http://codereview.stackexchange.com/questions/13512
*/
if (!is_string($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;
}
```
## Availability of `crypt()`'s Blowfish option
The `crypt()` function has ben part of PHP for a long time but not all PHP installations
Be careful of slow hash function implementations in PHP. The important thing is that the hash takes a lot of compute time *on the attackers equipment* and takes the minimum possible on yours. A hash implemented in PHP puts you at a disadvantage relative to the attacker. For example, imagine you iterate SHA-1 in in PHP for one second on a Micro instance on Amazon EC2 while the attacker has the same algorithm optimized to run on $5k's worth of modern GPUs. I don't know how many orders of magnitude faster the attacker's algorithm is than yours but I think its enough so that you should feel unsafe with such an implementation.
> that provides an API to simplify the use of `crypt()` for password storage.
> While this wiki article remains valid, it will in due course be rewritten
> to refer to the new class as well as explain how it works.
There are many tutorials and examples that show storage of passwords in a table.
Often the methods used are substandard and very easy to crack. There are many web pages and tutorials that show how to do it wrong.
[...]
```phpcrypt('EgzamplPassword', '$2a$10$1qAz2wSx3eDc4rFv5tGb5t')
```
[...]
```phpcrypt('EgzamplPassword', '$2a$10$1qAz2wSx3eDc4rFv5tGb5t12345678901234567890')
```
[...]
```phpcrypt('EgzamplPassword', '$2a$10$1qAz2wSx3eDc4rFv5tGb5e4jVuld5/KF2Kpy.B8D2XoC031sReFGi')
```
[...]
**Validate password against a stored hash**```php
$hash === crypt($password, $hash)
```
**NOTE:** We should use a constant-time string comparison algorithm to defeat
the possibility of
[timing attacks](http://blog.astrumfutura.com/2010/10/nanosecond-scale-remote-timing-attacks-on-php-applications-time-to-take-them-seriously/)
learning the result of validation. See below for an example.
[...]
}$rand = array();
for ($i = 0; $i < 8;
$rand[] = pack('S', mt_rand(0, 0xffff));
}
[...]
[sql]create table user (
)
~~~
[...]
```phpif ($password_hash === crypt($form->password, $record->passwordHash))
```
[...]
```## Constant-time string comparison.
This function is based on
[this](http://codereview.stackexchange.com/questions/13512/constant-time-string-comparision-in-php-to-prevent-timing-attacks)
and
[this](https://github.com/ircmaxell/password_compat/blob/master/lib/password.php).
```php
function same($a, $b) {
/**
* @see http://codereview.stackexchange.com/questions/13512
*/
if (!is_string($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;
}
```
## Availability of `crypt()`'s Blowfish option
The `crypt()` function has ben part of PHP for a long time but not all PHP installations
[...]
move to a host with an up-to-date PHP.Be careful of slow hash function implementations in PHP. The important thing is that the hash takes a lot of compute time *on the attackers equipment* and takes the minimum possible on yours. A hash implemented in PHP puts you at a disadvantage relative to the attacker. For example, imagine you iterate SHA-1 in in PHP for one second on a Micro instance on Amazon EC2 while the attacker has the same algorithm optimized to run on $5k's worth of modern GPUs. I don't know how many orders of magnitude faster the attacker's algorithm is than yours but I think its enough so that you should feel unsafe with such an implementation.
20 followers
Viewed: 179 403 times
Version: 1.1
Category: Tutorials
Written by: fsb
Last updated by: fsb
Created on: Nov 27, 2012
Last updated: 10 years ago
Revisions
View all history-
10 years ago by
fsb missing base64_encode()
-
11 years ago by
fsb Rewritten to accomodate 1.1.14
-
11 years ago by
samdark another try
-
11 years ago by
samdark trying to fix github link
-
11 years ago by
Ivo Renkema fixed a minor typo