Yii Password Strategies

Password strategies are specifications for how passwords should be encoded and verified and how complicated user supplied passwords should be. Out of the box it contains strategies for bcrypt and multiple rounds of hash functions e.g. sha1, as well as support for legacy password hashes like unsalted md5 and unsalted sha1. The aim is to allow multiple different password strategies to co-exist and to upgrade users from legacy hashes to new hashes when they login.

Why do I want this?

Imagine that you have a legacy application that uses simple, unsalted md5 based password hashing, which, in 2012 is considered completely insecure. You want to upgrade your password hashes, but you don't have access to the plain text passwords. In this scenario you can configure two password strategies, your old legacy one that uses md5, and your new shiney one that uses bcrypt. Then when users login to their accounts, their password will be verified using the legacy strategy, and if it matches, they will be seamlessly upgraded to the new bcrypt password strategy. For example:

class User extends \yii\db\ActiveRecord
{
  public function behaviors()
  {
    return [
      [
					"class" => "YiiPassword\Behavior",
				"defaultStrategyName" => "bcrypt",
				"strategies" => array(
					"bcrypt" => array(
						"class" => "YiiPassword\Strategies\Bcrypt",
						"workFactor" => 14
					),
					"legacy" => array(
						"class" => "YiiPassword\Strategies\LegacyMd5",
					)
				),
			)
		);
	}

	....
}

$user = User::model()->findByPK(1); // a user using the legacy password strategy
echo $user->password; // unsalted md5, horrible
$user->verifyPassword("password"); // verifies the password using the legacy strategy, and rehashes based on bcrypt strategy
echo $user->password; // now hashed with bcrpt

But this is also useful for modern applications, let's say you have a new webapp and you're doing The Right Thing and using bcrypt for your password hashing. You start off with a work factor of 12, but after a few months you decide you'd like to increase it to 15. Normally this would be quite difficult to accomplish because of all the users who've already signed up using the less secure hashes, but with password strategies, you can simply add another bcrpyt strategy with the desired work factor, set it to the default, and your users will be upgraded to the new strategy next time they login.

By default, YiiPassword\Behavior assumes that your model contains the following fields:

* *salt* - holds the per user salt used for hashing passwords
* *username* - holds the username
* *password* - holds the hashed password
* *passwordStrategy* - holds the name of the current password strategy for this user
* *requiresNewPassword* - a boolean field that determines whether the user should change their password or not

You can configure the field names on the behavior.

Also info: Using Bcrypt Strategy For New Application? - phpnode#10