title: What does the "stretches" of database_authenticatable of devise mean?
body: <p>I see in the config/initializers/devise.rb, there is a configuration called "config.stretches".</p>
  
  <pre><code># ==&gt; Configuration for :database_authenticatable
  # For bcrypt, this is the cost for hashing the password and defaults to 10. If
  # using other encryptors, it sets how many times you want the password re-encrypted.
  
  config.stretches = 10
  </code></pre>
  
  <p>I don't understand what does the <code>stretches</code> mean. It says it is the times I want the password "re-encrypted". Why and we the password will be re-encrypted? And why I should specify a "times"?</p>