title: Encrypt with GPG without adding stuff to the encrypted file?
body: <pre><code>$ echo "helloworld" &gt; text.txt
  $ cat text.txt
  helloworld
  
  $ gpg --cipher-algo AES256 --symmetric --armor text.txt
  gpg: gpg-agent is not available in this session
  $ ls
  text.txt text.txt.asc
  
  $ cat text.txt.asc
  -----BEGIN PGP MESSAGE-----
  Version: GnuPG v1
  
  jA0ECQMCnGyzh+mRmpBg0kgBfcqLbdAhLc+xwZDta3/kudi/f6MmjXUzFUbNFr3H
  IoXgqzjRqbeNESHd+nFSTxHQc8tXF80vXMdDzTy3HmD6ZWk3BvVx5Vo=
  =EviP
  -----END PGP MESSAGE-----
  </code></pre>
  
  <p>So, how can I avoid adding GPG stuff? I want only the encrypted bytes.  </p>
  
  <p>As AES256 is symmetric, I'd like to do something like this:  </p>
  
  <pre><code>1. Apply AES with keyA to "file_original.txt" and produce "file_keyA.txt"
  2. Apply AES with keyB to "file_keyA.txt" and get "file_keyA_keyB.txt"
  3. Apply AES with keyA to "file_keyA_keyB.txt" and get "file_keyB.txt"
  4. Apply AES with keyB to "file_keyB" and get "file_original.txt"
  </code></pre>
  
  <p>So, if I'm A, and want to send "sometext" to my friend B:  </p>
  
  <ol>
  <li>I send "sometext" encrypted with GPG with keyA to my friend.  </li>
  <li>He send back to me his text encrypted with his keyB too.  </li>
  <li>I decrypt with my keyA and send back to him.  </li>
  <li>He should apply keyB and get "sometext".  </li>
  </ol>
  
  <p>It should be possible if I use gpg with AES and my friend another software or another symmetric algorithm without knowing my keyA. But it's only possible if gpg (or his software) doesn't add stuff to the encrypted file. I want to apply only the algorithm AES, so I can encrypt multiple times with the same key and get the original.  </p>