How to use PHP's password_hash to hash and verify passwords

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When it comes to secure password storage, it is essential to use a hashing algorithm. PHP provides the built-in function password_hash() specifically designed for this purpose. In this article, we will explore how to effectively use password_hash() to hash and verify passwords in PHP.

Understanding password hashing

Before diving into password_hash(), let's have a brief understanding of password hashing and why it is crucial for proper security.

Password hashing is the process of converting a plain-text password into a fixed-length string of characters, known as the hash. The primary purpose of hashing is to protect user passwords in case of a data breach.

When a user creates an account or updates their password, the password provided is transformed into a hash and stored in a database. During login attempts, the provided password is hashed again, and the generated hash is compared with the stored hash. If they match, the password is considered valid.

Using password_hash() in PHP

In PHP, the password_hash() function simplifies the process of password hashing by abstracting all the details. This function uses the secure bcrypt algorithm under the hood, ensuring that the resulting hashes are strong and resistant to various attacks.

Let's take a look at the basic usage of password_hash():

$password = "mySecurePassword";
$hash = password_hash($password, PASSWORD_DEFAULT);

In the above example, we pass the original plain-text password to password_hash(), along with the PASSWORD_DEFAULT constant. The constant tells PHP to use the default hashing algorithm, which is currently bcrypt.

The function will generate a hash of the password, which can be stored in a database or any other persistent storage. It is essential to note that every time you hash the same password, the resulting hash will be different due to the random salt generated by bcrypt.

Verifying passwords with password_verify()

To validate a user's password, we need to compare the provided password with the stored hash. PHP provides the password_verify() function for this task:

$password = "mySecurePassword";
$hash = "theSavedHashFromTheDatabase";

if (password_verify($password, $hash)) {
    // Password is correct
} else {
    // Password is incorrect
}

In the example above, we pass both the plain-text password and the stored hash to password_verify(). The function will compare the provided password with the saved hash and return true if they match, or false otherwise. This way, you can easily determine whether the password is valid or not.

Why use password_hash() instead of custom hashing?

When it comes to password hashing, it is highly recommended to use a secure and well-tested algorithm like bcrypt provided by password_hash() over creating custom hashing logic.

  • Strength and Efficiency: The bcrypt algorithm used by password_hash() is designed to be slow and computationally expensive, which makes it resistant to brute-force attacks. It automatically handles the complexity of salting and stretching the passwords, providing a secure solution without the need for additional coding.
  • Future-proof: By relying on password_hash(), you can benefit from any future security improvements and algorithm updates without modifying your code explicitly.
  • Easy to use: The password_hash() function is simple to implement and provides a consistent and secure approach for password hashing.

Handling password upgrades with password_needs_rehash()

As technology evolves, so do the best practices for password hashing. It might be necessary to update the hashing algorithm or increase the cost factor of the existing algorithm used by password_hash().

PHP provides the password_needs_rehash() function to check if a saved hash needs to be rehashed:

$hash = "theSavedHashFromTheDatabase";

if (password_needs_rehash($hash, PASSWORD_DEFAULT)) {
    $newHash = password_hash($password, PASSWORD_DEFAULT);
    // save $newHash to the database
}

In the example above, we pass the stored hash and the hashing algorithm constant to password_needs_rehash(). If the hash needs an upgrade, based on the current settings defined in PHP, you can generate a new and more secure hash using password_hash() and update the saved hash with the new one.

This way, you can ensure that older passwords are gradually upgraded to the latest hashing algorithms without causing any inconvenience to your users.

Conclusion

Implementing secure password storage is a crucial aspect of web development. By using PHP's password_hash() function, you can easily hash and verify passwords without worrying about the low-level implementation details.

Remember to always use the default PASSWORD_DEFAULT algorithm, as it ensures the use of the strongest algorithm available at the time.

By following best practices like hashing with bcrypt, comparing hashes with password_verify(), and adapting the hashing algorithm with password_needs_rehash(), you can build a robust authentication system that protects your users' passwords.

For more information, you can refer to the official PHP documentation on password_hash() and password_verify().

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