title: Where 2x prefix are used in BCrypt?
body: <p>The question is the same title, Where $2x$ is used in BCrypt?</p>
  
  <p>The following scenario is right?</p>
  
  <p>We have a set of passwords that hashed with <code>$2a$</code> prefix already, when the Server PHP version was earlier <code>5.3.7</code>. Now we upgraded the PHP to <code>5.3.7+</code>, now we must firstly verify previous passwords with <code>$2x$</code> algorithm then rehash the password with <code>$2y$</code> prefix. That's right?</p>