title: Cipher.init() required for each message?
body: <p>Assume two clients are exchanging secure messages back and forth.</p>
  
  <p>Must this block be run every time for each message, or can any step(s) be done just once at start:</p>
  
  <pre><code>cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
  cipher.init(Cipher.ENCRYPT_MODE, keySpec);
  output = cipher.doFinal(content);
  </code></pre>
  
  <p>I guess to lend some context- although I don't (yet) understand the internals completely, it is my understanding that for security purposes it's important to change the IV for each message. So I think the answer to this question will depend on whether that step happens under the hood at the doFinal() stage or init()....?</p>