password_needs_rehash

(PHP 5 >= 5.5.0, PHP 7)

password_needs_rehash — Sprawdza czy podany hash pasuje do podanych opcji

Opis

password_needs_rehash ( string $hash , integer $algorytm [, array $opcje ] ) : boolean

Ta funkcja sprawdza czy podany hash implementuje podany algorytm i opcje. Jeżeli nie, przyjmuje się, że hash powinien zostać wygenerowany ponownie.

Parametry

hash: Skrót wygenerowany przez password_hash().
algorytm: Stała algorytmu hasła wyznaczająca algorytm stosowany przy generowaniu skrótu hasła.
opcje: Tablica asocjacyjna zawierająca opcje. Zobacz stałe algorytmów haseł, aby poznać opcje wspierane przez każdy z algorytmów.

Przykłady

Przykład #1 Przykład użycia password_needs_rehash()


<?php

$password = 'rasmuslerdorf';
$hash = '$2y$10$YCFsG6elYca568hBi2pZ0.3LDL5wjgxct1N8w/oLR/jfHsiQwCqTS';

// Parametr cost może zmieniać się z czasem, wraz z poprawą sprzętu
$options = array('cost' => 11);

// Porównaj trzymany hash z hasłem w czystym tekście
if (password_verify($password, $hash)) {
    // Sprawdź czy jest dostępny nowszy algorytm hashujący
    // lub czy zmienił się parametr cost
    if (password_needs_rehash($hash, PASSWORD_DEFAULT, $options)) {
        // Jeśli tak, stwórz nowy hash i zamień stary
        $newHash = password_hash($password, PASSWORD_DEFAULT, $options);
    }

    // Zaloguj użytkownika
}
?>

Zwracane wartości

Zwraca TRUE jeżeli wymagany jest rehash, aby spełnić podany algorytm i opcje lub FALSE w przeciwnym wypadku.

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User Contributed Notes 4 notes

down

php dot net at muer dot nl ¶

9 years ago


nick, this function cannot check if a string is a MD5 or SHA1 hash. It can only tell you if a password, hashed using the password_hash function, needs to be put through the hashing function again to keep up to date with the new defaults.

The only time you can use this function is when your user logs in and you have already checked by means of password_verify that the password entered is actually correct. At that point, if password_needs_rehash returns true, you can put the plain text password through the password_hash function.

down

nick at nickstallman dot net ¶

10 years ago


ydroneaud this would be used on a login page, not at any other time.

So if you have a site with MD5 passwords for example, and wish to upgrade to SHA256 for additional security you would put this check in the login script.

This function will take a user's hash and say if it is SHA256, if it isn't then you can take the user's password which you still have as plaintext and rehash it as SHA256.

This lets you gradually update the hashes in your database without disrupting any features or resetting passwords.

down

admin at torntech dot com ¶

9 years ago


Some other use-cases for the password_needs_rehash function is when you have specified using the PASSWORD_DEFAULT algorithm for password_hash.
As mentioned on the Password Hashing Predefined Constants and password_hash pages, the algorithm used by PASSWORD_DEFAULT is subject to change as different versions of PHP are released.
Additionally password_needs_rehash would be used if you have changed the optional cost or static salt (DO NOT USE A STATIC SALT) requirements of your password_hash options.

Full example:

<?php

$new = [
    'options' => ['cost' => 11],
    'algo' => PASSWORD_DEFAULT,
    'hash' => null
];

$password = 'rasmuslerdorf';

//stored hash of password
$oldHash = '$2y$07$BCryptRequires22Chrcte/VlQH0piJtjXl.0t1XkA8pw9dMXTpOq';

//verify stored hash against plain-text password
if (true === password_verify($password, $oldHash)) {
    //verify legacy password to new password_hash options
    if (true === password_needs_rehash($oldHash, $new['algo'], $new['options'])) {
        //rehash/store plain-text password using new hash
        $newHash = password_hash($password, $new['algo'], $new['options']);
        echo $newHash;
    }
}
?>

The above example will output something similar to:
$2y$11$Wu5rN3u38.g/XWdUeA6Wj.PD.F0fLXXmZrMNFyzzg2UxkVmxlk41W

down

geekasylum at google mail ¶

5 years ago


This function can indeed be used to assist in transparently updating legacy passwords (those not using the password_hash() function - eg: perhaps something using MD5 or SHA1)

In legacy sites, when authenticating a user (during login) first check the password using password_verify(). If that fails it may simply be because the user's password hash was created long ago by a legacy or home-brew password algorithm.

You can then re-check the password against the site's legacy password algorithm.  If that fails too, then the login fails, since the supplied password did not authenticate against either the new, or the old password tests.

If any one of those two test was successfull, you know that the password is good so you would then call password_needs_rehash() on the stored hash, and it will properly indicate if the password hash needs to be re-computed, either because it's an unrecognised (legacy) hash or it's a modern hash created by password_hash(), which may just need its cost index updated.

Simply store the recomputed hash in the database and you now have a password_verify() compatible password for that user and the second test can be skipped in future logins (but still check if it needs rehashing).

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