php[tek] 2017: Atlanta


(PHP 5 >= 5.5.0, PHP 7)

password_needs_rehashÜberprüft, ob der übergebene Hash mit den übergebenen Optionen übereinstimmt


boolean password_needs_rehash ( string $hash , string $algo [, string $options ] )

Diese Funktion überprüft, ob der übergebene Hash den gleichen Algorithmus und die gleichen Optionen nutzt, wie in den übergebenen Optionen abgegeben. Falls nicht, wird angenommen, dass erneutes Hashen notwendig ist.



Ein Hash, der durch password_hash() erzeugt wurde.


Eine Konstante für den Passwort-Algorithmus, die den Algorithmus zum hashen des Passwortes angibt.


Ein assoziatives Array mit Optionen. Siehe auch Konstanten für Passwort-Algorithmen für Informationen zu den von dein jeweiligen Algorithmen unterstützten Optionen.


Gibt TRUE zurück, falls der Hash erneut gehasht werden muss, damit die übergebenen Parameter algo und options übereinstimmen, sonst FALSE.

add a note add a note

User Contributed Notes 5 notes

admin at torntech dot com
2 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:


= [
'options' => ['cost' => 11],
'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']);

The above example will output something similar to:
nick at nickstallman dot net
3 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.
php dot net at muer dot nl
2 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.
smartclashcoc at gmail dot com
15 days ago
The PHP function checks whether it is required to rehash the password or not. It does not give us a new hash whenever we request it to do so. Is there any other function that generates a new hash when we call that function ?
ydroneaud at opteya dot com
3 years ago
According to the documentation, it's checking if the given hashed password string is compatible with the provided algorithm (and options, but not salt), eg. it's checking if the hashed password string was generated with the provided algorithm (and options, but not salt).

There's nothing to 'rehash' in its parameters ... especially not the already hashed password string, and the password "stored" in the hashed password string is not supposed to be known, it's not in clear, it's a secret.

The name of the function seems misleading, this function should have been called "password_hash_compatible()" instead.

This function could be use to check if a password database/a hashed password string (hashed by function "password_hash()") need to be upgraded to a stronger password hashing/storage scheme: if the function returns false,  a new password will have to be set for the user, hashed with the new, stronger, algorithm/options.

One should carefully think before using this function to support multiple algorithms/options in one database, eg. support "legacy scheme" passwords + "new scheme" ...
To Top