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password_needs_rehash

(PHP 5 >= 5.5.0, PHP 7)

password_needs_rehashVerifica se o hash recebido corresponde com as opções recebidas

Descrição

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

Esta função verifica se o hash fornecido implementa o algoritmo e as opções indicadas. Se não, ela assume que o hash precisa ser regenerado.

Parâmetros

hash

Um hash criado por password_hash().

algo

Uma constante de algoritmo de senha indicando qual algoritmo utilizar no hash de senha.

options

Um array associativo contendo opções. Veja as constantes de algoritmo de senha sobre detalhes das opções suportadas por cada algoritmo.

Exemplos

Exemplo #1 Utilização de password_needs_rehash()

<?php

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

// The cost parameter can change over time as hardware improves
$options = array('cost' => 11);

// Verify stored hash against plain-text password
if (password_verify($password$hash)) {
    
// Check if a newer hashing algorithm is available
    // or the cost has changed
    
if (password_needs_rehash($hashPASSWORD_DEFAULT$options)) {
        
// If so, create a new hash, and replace the old one
        
$newHash password_hash($passwordPASSWORD_DEFAULT$options);
    }

    
// Log user in
}
?>

Valor Retornado

Retorna TRUE se o hash deve ser regenerado para corresponder ao algo e options indicados, ou FALSE caso contrário.

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User Contributed Notes 3 notes

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20
nick at nickstallman dot net
4 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.
up
12
admin at torntech dot com
3 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
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10
php dot net at muer dot nl
3 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.
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