Timing attack safe string comparison

Descrierea

bool hash_equals ( string $known_string , string $user_string )

Compares two strings using the same time whether they're equal or not.

This function should be used to mitigate timing attacks; for instance, when testing crypt() password hashes.

Parametri

known_string: The string of known length to compare against
user_string: The user-supplied string

Valorile întoarse

Returns TRUE when the two strings are equal, FALSE otherwise.

Erori/Excepții

Emits an E_WARNING message when either of the supplied parameters is not a string.

Exemple

Example #1 example


<?php
$expected  = crypt('12345', '$2a$07$usesomesillystringforsalt$');
$correct   = crypt('12345', '$2a$07$usesomesillystringforsalt$');
$incorrect = crypt('apple',  '$2a$07$usesomesillystringforsalt$');

var_dump(hash_equals($expected, $correct));
var_dump(hash_equals($expected, $incorrect));
?>

Exemplul de mai sus va afișa:

bool(true)
bool(false)

Note

Notă:
Both arguments must be of the same length to be compared successfully. When arguments of differing length are supplied, FALSE is returned immediately and the length of the known string may be leaked in case of a timing attack.

Notă:
It is important to provide the user-supplied string as the second parameter, rather than the first.