password_needs_rehash checks whether a stored password hash should be regenerated because the selected algorithm or options changed.
The examples explain the data format, expected results and the difference between this API and nearby cryptographic operations.
What It Does
The operation is intended for: password_needs_rehash checks whether a stored password hash should be regenerated because the selected algorithm or options changed.
Part of core PHP or a normally bundled standard extension; check your deployment configuration.
Syntax and Return Value
password_needs_rehash(string $hash, string|int|null $algo, array $options = ...): bool| Parameter | Purpose |
|---|---|
| $hash (string) | Previously stored hash or digest to inspect or compare. |
| $algo (string|int|null) | The exact algorithm identifier supported by this API. |
| $options (array) | Driver or algorithm-specific options; avoid unchecked user-controlled settings. |
The declared return type is shown above. Errors can include false results or exceptions depending on this API: Never store plaintext passwords or compare password hashes with ==; salts and hash algorithm metadata belong in the stored hash.
Example 1: Basic Operation
Inspect the expected result: do not print secrets or reuse illustrative credentials in production.
<?php
$hash = password_hash("demo-password", PASSWORD_BCRYPT, ["cost" => 10]);
var_dump(password_needs_rehash($hash, PASSWORD_BCRYPT, ["cost" => 12]));Example 2: A Different Use Case
Compare a matching hashing policy against a stronger new work factor.
<?php
$hash = password_hash('example', PASSWORD_BCRYPT, ['cost' => 10]);
var_dump(password_needs_rehash($hash, PASSWORD_BCRYPT, ['cost' => 10]) === false);Practical Example: Checking the Result
Compare a matching hashing policy against a stronger new work factor.
<?php
$hash = password_hash('example', PASSWORD_BCRYPT, ['cost' => 10]);
var_dump(password_needs_rehash($hash, PASSWORD_BCRYPT, ['cost' => 12]));Important Behavior and Edge Cases
Never store plaintext passwords or compare password hashes with ==; salts and hash algorithm metadata belong in the stored hash.
Password storage requires purpose-built salted, slow hashes; a fast cryptographic digest must never be used as a substitute.
Comparison with Related Functions
| Approach | Key distinction |
|---|---|
| password_needs_rehash | password_needs_rehash checks whether a stored password hash should be regenerated because the selected algorithm or options changed. |
| Related technique | password_hash and password_verify are the preferred pair for new PHP password authentication. |
Common Beginner Mistakes
| Mistake | Correct approach |
|---|---|
| Confusing this operation with a neighboring cryptographic or security mechanism | password_hash and password_verify are the preferred pair for new PHP password authentication. |
| Ignoring a security prerequisite or failure case | Never store plaintext passwords or compare password hashes with ==; salts and hash algorithm metadata belong in the stored hash. |
Key Takeaways
- password_needs_rehash checks whether a stored password hash should be regenerated because the selected algorithm or options changed.
- Never store plaintext passwords or compare password hashes with ==; salts and hash algorithm metadata belong in the stored hash.
- password_hash and password_verify are the preferred pair for new PHP password authentication.
Apply this behavior to a real application only after confirming the required extension, configuration and failure handling on the deployment runtime.