title: Encrypt, decrypt using Rails
body: <p>I saw a while ago the possibility to decrypt and encrypt strings in rails without including any library, but I can't find the blog post.</p>
  
  <p>I want to be able to encrypt and decrypt strings without including anything.
  Using the same key has for the everything else in rails, signed cookies for example.</p>
  
  <p>Any ideas?</p>