为什么 password_verify 返回 false？

Question

Why does password_verify return false?

_{This question is intended to be canonical and has been created simply based on the amount of questions that have been asked on this topic.}

Answer 1

There are a variety of reasons why password_verify could be returning false, it can range from the setup of your table to the actual comparing of the password, below are the common causes of it failing.

Column Setup

• The length of the password column in your table is too short:

  • If you are using PASSWORD_DEFAULT then it is recommended to store the result in a database column that can expand beyond 60 characters (255 characters would be a good choice).
  • If you are using PASSWORD_BCRYPT then it is recommended to store the result in a database column that is 60 characters because PASSWORD_BCRYPT will always result in a 60 character string or FALSE on failure.

Password Sanitization

Another common cause is when developers try to "clean" the user's password to prevent it from being malicious, as a result, this causes the input to be different to what is being stored in the table. It is not even necessary to escape the input, you should use prepared statements instead. You shouldn't even trim the passwords as that could change that which was originally provided.

Password Verification

When using password_verify you need to compare the plaintext password with the hash from the database/file/some-other-storage-method, not compare hashes (the implication here being that you need to have stored the hashed password of the user when they register):

<?php

$hashed = password_hash('test', PASSWORD_DEFAULT);
$password = 'test';

if (password_verify($password, $hashed)) {
  echo 'success';
} else {
  echo 'fail';
}

?>

Ensure that you are actually passing a hash to password_verify and not something else by dumping it.

Repl

Hardcoded Passwords

In the instance that you are using a hardcoded hash and you are facing issues, ensure that you are using single quotes instead of double quotes when storing the value in the variable as the $ will be interpreted in when using double quotes:

<?php
// Undefined variable: QHpfI0MfQWjvsVQWRdFHSOX6WqG8LSf0iFGiKs0Fz0RvqhpFOpAKu :1
$incorrect = "$2y$10$QHpfI0MfQWjvsVQWRdFHSOX6WqG8LSf0iFGiKs0Fz0RvqhpFOpAKu";

$correct = '$2y$10$QHpfI0MfQWjvsVQWRdFHSOX6WqG8LSf0iFGiKs0Fz0RvqhpFOpAKu';
?>

Repl - Comment out respectively.

Troubleshooting

var_dump() the hashed password on registration right before you insert it into your database, and var_dump() it again after you fetch it from your database when you are about to password_verify() it. Ensure both hashes are identical. If they are, and the plaintext passwords are identical too, there's no reason for password_verify to fail. It only fails if the hash gets modified in some way on its roundtrip through the database, or if the plaintext passwords aren't identical.

Ensure that you are passing a correct algorithm to password_hash has the second parameter.

Addendum

As per the documentation:

Caution It is strongly recommended that you do not generate your own salt for this function. It will create a secure salt automatically for you if you do not specify one.

As noted above, providing the salt option in PHP 7.0 will generate a deprecation warning. Support for providing a salt manually may be removed in a future PHP release.

Answer 2

Check the parameters order

Just to point something that happened to me, who was reading this same topic trying to solve my problem minutes ago, and can help you to solve the problem as well.
See if you are giving the parameters for password_verify() in the right order:

password_verify(string $password , string $hash )

password is the password you received by post or other method and are trying to validate.

hash is the hash that you want to compare the password to.(eg The password hash stored in your Data Base)

It happened to me that I inverted the order of the parameters, so the result wasn't coming as I expected to.