Password Hashing and Verification

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Password Hashing and Verification

Most applications use passwords to login users. These passwords should be hashed to securely store them. Symfony's PasswordHasher component provides all utilities to safely hash and verify passwords.

Make sure it is installed by running:

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$ composer require symfony/password-hasher

Configuring a Password Hasher

Before hashing passwords, you must configure a hasher using the password_hashers option. You must configure the hashing algorithm and optionally some algorithm options:

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# config/packages/security.yaml
security:
    # ...

    password_hashers:
        # auto hasher with default options for the User class (and children)
        App\Entity\User: 'auto'

        # auto hasher with custom options for all PasswordAuthenticatedUserInterface instances
        Symfony\Component\Security\Core\User\PasswordAuthenticatedUserInterface:
            algorithm: 'auto'
            cost:      15

In this example, the "auto" algorithm is used. This hasher automatically selects the most secure algorithm available on your system. Combined with password migration, this allows you to always secure passwords in the safest way possible (even when new algorithms are introduced in future PHP releases).

Further in this article, you can find a full reference of all supported algorithms.

Tip

Hashing passwords is resource intensive and takes time in order to generate secure password hashes. In general, this makes your password hashing more secure.

In tests however, secure hashes are not important, so you can change the password hasher configuration in test environment to run tests faster:

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# config/packages/test/security.yaml
security:
    # ...

    password_hashers:
        # Use your user class name here
        App\Entity\User:
            algorithm: plaintext # disable hashing (only do this in tests!)

        # or use the lowest possible values
        App\Entity\User:
            algorithm: auto # This should be the same value as in config/packages/security.yaml
            cost: 4 # Lowest possible value for bcrypt
            time_cost: 3 # Lowest possible value for argon
            memory_cost: 10 # Lowest possible value for argon

Hashing the Password

After configuring the correct algorithm, you can use the UserPasswordHasherInterface to hash and verify the passwords:

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// src/Controller/RegistrationController.php
namespace App\Controller;

// ...
use
Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException;
use Symfony\Component\PasswordHasher\Hasher\UserPasswordHasherInterface;

class UserController extends AbstractController
{
    public function registration(UserPasswordHasherInterface $passwordHasher)
    {
        // ... e.g. get the user data from a registration form
        $user = new User(...);
        $plaintextPassword = ...;

        // hash the password (based on the security.yaml config for the $user class)
        $hashedPassword = $passwordHasher->hashPassword(
            $user,
            $plaintextPassword
        );
        $user->setPassword($hashedPassword);

        // ...
    }

    public function delete(UserPasswordHasherInterface $passwordHasher, UserInterface $user)
    {
        // ... e.g. get the password from a "confirm deletion" dialog
        $plaintextPassword = ...;

        if (!$passwordHasher->isPasswordValid($user, $plaintextPassword)) {
            throw new AccessDeniedHttpException();
        }
    }
}

Reset Password

Using MakerBundle and SymfonyCastsResetPasswordBundle, you can create a secure out of the box solution to handle forgotten passwords. First, install the SymfonyCastsResetPasswordBundle:

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$ composer require symfonycasts/reset-password-bundle

Then, use the make:reset-password command. This asks you a few questions about your app and generates all the files you need! After, you'll see a success message and a list of any other steps you need to do.

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$ php bin/console make:reset-password

You can customize the reset password bundle's behavior by updating the reset_password.yaml file. For more information on the configuration, check out the SymfonyCastsResetPasswordBundle guide.

Password Migration

In order to protect passwords, it is recommended to store them using the latest hash algorithms. This means that if a better hash algorithm is supported on your system, the user's password should be rehashed using the newer algorithm and stored. That's possible with the migrate_from option:

  1. Configure a new Hasher Using "migrate_from"
  2. Upgrade the Password
  3. Optionally, Trigger Password Migration From a Custom Hasher

Configure a new Hasher Using "migrate_from"

When a better hashing algorithm becomes available, you should keep the existing hasher(s), rename it, and then define the new one. Set the migrate_from option on the new hasher to point to the old, legacy hasher(s):

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# config/packages/security.yaml
security:
    # ...

    password_hashers:
        # a hasher used in the past for some users
        legacy:
            algorithm: sha256
            encode_as_base64: false
            iterations: 1

        App\Entity\User:
            # the new hasher, along with its options
            algorithm: sodium
            migrate_from:
                - bcrypt # uses the "bcrypt" hasher with the default options
                - legacy # uses the "legacy" hasher configured above

With this setup:

  • New users will be hashed with the new algorithm;
  • Whenever a user logs in whose password is still stored using the old algorithm, Symfony will verify the password with the old algorithm and then rehash and update the password using the new algorithm.

Tip

The auto, native, bcrypt and argon hashers automatically enable password migration using the following list of migrate_from algorithms:

  1. PBKDF2 (which uses hash_pbkdf2);
  2. Message digest (which uses hash)

Both use the hash_algorithm setting as the algorithm. It is recommended to use migrate_from instead of hash_algorithm, unless the auto hasher is used.

Upgrade the Password

Upon successful login, the Security system checks whether a better algorithm is available to hash the user's password. If it is, it'll hash the correct password using the new hash. When using a custom authenticator, you must use the PasswordCredentials in the security passport.

You can enable the upgrade behavior by implementing how this newly hashed password should be stored:

After this, you're done and passwords are always hashed as securely as possible!

Note

When using the PasswordHasher component outside a Symfony application, you must manually use the PasswordHasherInterface::needsRehash() method to check if a rehash is needed and PasswordHasherInterface::hash() method to rehash the plaintext password using the new algorithm.

Upgrade the Password when using Doctrine

When using the entity user provider, implement PasswordUpgraderInterface in the UserRepository (see the Doctrine docs for information on how to create this class if it's not already created). This interface implements storing the newly created password hash:

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// src/Repository/UserRepository.php
namespace App\Repository;

// ...
use Symfony\Component\Security\Core\User\PasswordUpgraderInterface;

class UserRepository extends EntityRepository implements PasswordUpgraderInterface
{
    // ...

    public function upgradePassword(UserInterface $user, string $newHashedPassword): void
    {
        // set the new hashed password on the User object
        $user->setPassword($newHashedPassword);

        // execute the queries on the database
        $this->getEntityManager()->flush();
    }
}

Upgrade the Password when using a Custom User Provider

If you're using a custom user provider, implement the PasswordUpgraderInterface in the user provider:

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// src/Security/UserProvider.php
namespace App\Security;

// ...
use Symfony\Component\Security\Core\User\PasswordUpgraderInterface;

class UserProvider implements UserProviderInterface, PasswordUpgraderInterface
{
    // ...

    public function upgradePassword(UserInterface $user, string $newHashedPassword): void
    {
        // set the new hashed password on the User object
        $user->setPassword($newHashedPassword);

        // ... store the new password
    }
}

Trigger Password Migration From a Custom Hasher

If you're using a custom password hasher, you can trigger the password migration by returning true in the needsRehash() method:

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// src/Security/CustomPasswordHasher.php
namespace App\Security;

// ...
use Symfony\Component\PasswordHasher\Hasher\UserPasswordHasherInterface;

class CustomPasswordHasher implements UserPasswordHasherInterface
{
    // ...

    public function needsRehash(string $hashed): bool
    {
        // check whether the current password is hashed using an outdated hasher
        $hashIsOutdated = ...;

        return $hashIsOutdated;
    }
}

Named Password Hashers

Usually, the same password hasher is used for all users by configuring it to apply to all instances of a specific class. Another option is to use a "named" hasher and then select which hasher you want to use dynamically.

By default (as shown at the start of the article), the auto algorithm is used for App\Entity\User.

This may be secure enough for a regular user, but what if you want your admins to have a stronger algorithm, for example auto with a higher cost. This can be done with named hashers:

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# config/packages/security.yaml
security:
    # ...
    password_hashers:
        harsh:
            algorithm: auto
            cost: 15

This creates a hasher named harsh. In order for a User instance to use it, the class must implement PasswordHasherAwareInterface. The interface requires one method - getPasswordHasherName() - which should return the name of the hasher to use:

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// src/Entity/User.php
namespace App\Entity;

use Symfony\Component\PasswordHasher\Hasher\PasswordHasherAwareInterface;
use Symfony\Component\Security\Core\User\PasswordAuthenticatedUserInterface;
use Symfony\Component\Security\Core\User\UserInterface;

class User implements
    UserInterface,
    PasswordAuthenticatedUserInterface,
    PasswordHasherAwareInterface
{
    // ...

    public function getPasswordHasherName(): ?string
    {
        if ($this->isAdmin()) {
            return 'harsh';
        }

        return null; // use the default hasher
    }
}

If you created your own password hasher implementing the PasswordHasherInterface, you must register a service for it in order to use it as a named hasher:

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# config/packages/security.yaml
security:
    # ...
    password_hashers:
        app_hasher:
            id: 'App\Security\Hasher\MyCustomPasswordHasher'

This creates a hasher named app_hasher from a service with the ID App\Security\Hasher\MyCustomPasswordHasher.

Supported Algorithms

The "auto" Hasher

It automatically selects the best available hasher (currently Bcrypt). If PHP or Symfony adds new password hashers in the future, it might select a different hasher.

Because of this, the length of the hashed passwords may change in the future, so make sure to allocate enough space for them to be persisted (varchar(255) should be a good setting).

The Bcrypt Password Hasher

It produces hashed passwords with the bcrypt password hashing function. Hashed passwords are 60 characters long, so make sure to allocate enough space for them to be persisted. Also, passwords include the cryptographic salt inside them (it's generated automatically for each new password) so you don't have to deal with it.

Its only configuration option is cost, which is an integer in the range of 4-31 (by default, 13). Each single increment of the cost doubles the time it takes to hash a password. It's designed this way so the password strength can be adapted to the future improvements in computation power.

You can change the cost at any time — even if you already have some passwords hashed using a different cost. New passwords will be hashed using the new cost, while the already hashed ones will be validated using a cost that was used back when they were hashed.

Tip

A simple technique to make tests much faster when using BCrypt is to set the cost to 4, which is the minimum value allowed, in the test environment configuration.

The Sodium Password Hasher

It uses the Argon2 key derivation function. Argon2 support was introduced in PHP 7.2 by bundling the libsodium extension.

The hashed passwords are 96 characters long, but due to the hashing requirements saved in the resulting hash this may change in the future, so make sure to allocate enough space for them to be persisted. Also, passwords include the cryptographic salt inside them (it's generated automatically for each new password) so you don't have to deal with it.

The PBKDF2 Hasher

Using the PBKDF2 hasher is no longer recommended since PHP added support for Sodium and BCrypt. Legacy application still using it are encouraged to upgrade to those newer hashing algorithms.

Creating a custom Password Hasher

If you need to create your own, it needs to follow these rules:

  1. The class must implement PasswordHasherInterface (you can also implement LegacyPasswordHasherInterface if your hash algorithm uses a separate salt);

  2. The implementations of hash() and verify() must validate that the password length is no longer than 4096 characters. This is for security reasons (see CVE-2013-5750).

    You can use the isPasswordTooLong() method for this check.

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// src/Security/Hasher/CustomVerySecureHasher.php
namespace App\Security\Hasher;

use Symfony\Component\PasswordHasher\Exception\InvalidPasswordException;
use Symfony\Component\PasswordHasher\Hasher\CheckPasswordLengthTrait;
use Symfony\Component\PasswordHasher\PasswordHasherInterface;

class CustomVerySecureHasher implements PasswordHasherInterface
{
    use CheckPasswordLengthTrait;

    public function hash(string $plainPassword): string
    {
        if ($this->isPasswordTooLong($plainPassword)) {
            throw new InvalidPasswordException();
        }

        // ... hash the plain password in a secure way

        return $hashedPassword;
    }

    public function verify(string $hashedPassword, string $plainPassword): bool
    {
        if ('' === $plainPassword || $this->isPasswordTooLong($plainPassword)) {
            return false;
        }

        // ... validate if the password equals the user's password in a secure way

        return $passwordIsValid;
    }
}

Now, define a password hasher using the id setting:

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# config/packages/security.yaml
security:
    # ...
    password_hashers:
        app_hasher:
            # the service ID of your custom hasher (the FQCN using the default services.yaml)
            id: 'App\Security\Hasher\MyCustomPasswordHasher'
This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.
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