Creates a unique hash value for use in time-dependent per-user URLs.
This hash is normally used to build a unique and secure URL that is sent to the user by email for purposes such as resetting the user's password. In order to validate the URL, the same hash can be generated again, from the same information, and compared to the hash value from the URL. The URL normally contains both the time stamp and the numeric user ID. The login name and hashed password are retrieved from the database as necessary. For a usage example, see user_cancel_url() and user_cancel_confirm().
$password: The hashed user account password value.
$timestamp: A unix timestamp.
$login: The user account login name.
A string that is safe for use in URLs and SQL statements.
function user_pass_rehash($password, $timestamp, $login) {
return drupal_hmac_base64($timestamp . $login, drupal_get_hash_salt() . $password);
}