title: How practical would it be to repeatedly encrypt a given file?
body: <p>I'm currently experimenting with both public-key and personal file encryption. The programs I use have 2048 bit RSA and 256 bit AES level encryption respectively. As a newbie to this stuff (I've only been a cypherpunk for about a month now - and am a little new to information systems) I'm not familiar with RSA algorithms, but that's not relevant here. </p>
  
  <p>I know that unless some secret lab or NSA program happens to have a quantum computer, it is currently impossible to brute force hack the level of security these programs provide, but I was wondering how much more secure it would be to encrypt a file over and over again.</p>
  
  <p>In a nutshell, what I would like to know is this: </p>
  
  <ol>
  <li>When I encrypt a file using 256-bit AES, and then encrypt the already encrypted file once more (using 256 again), do I now have the equivalent of 512-bit AES security? This is pretty much a question of whether or not the the number of possible keys a brute force method would potentially have to test would be <strong><em>2</em></strong> x 2 to the 256th power or 2 to the 256th power <strong><em>squared</em></strong>. Being pessimistic, I think it is the former but I was wondering if 512-AES really is achievable by simply encrypting with 256-AES twice?</li>
  <li>Once a file is encrypted several times so that you must keep using different keys or keep putting in passwords at each level of encryption, would someone** even recognize if they have gotten through the first level of encryption? I was thinking that perhaps - if one were to encrypt a file several times requiring several different passwords - a cracker would not have any way of knowing if they have even broken through the first level of encryption since all they would have would still be an encrypted file.  </li>
  </ol>
  
  <p>Here's an example:</p>
  
  <ul>
  <li>Decrypted file</li>
  <li>DKE$jptid UiWe</li>
  <li>oxfialehv u%uk</li>
  </ul>
  
  <p>Pretend for a moment that the last sequence is what a cracker had to work with - to brute-force their way back to the original file, the result they would have to get (prior to cracking through the next level of encryption) would still appear to be a totally useless file (the second line) once they break through the first level of encryption. Does this mean that anyone attempting to use brute-force would have no way of getting back to the original file since they presumably would still see nothing but encrypted files?</p>
  
  <p>These are basically two questions that deal with the same thing: the effect of encrypting the same file over and over again. I have searched the web to find out what effect repeated encryption has on making a file secure, but aside from reading an anecdote somewhere that the answer to the first question is no, I have found nothing that pertains to the second spin on the same topic. I am especially curious about that last question.</p>
  
  <p>**Assuming hypothetically that they somehow brute-forced their way through weak passwords - since this appears to be a technological possibility with 256-AES right now if you know how to make secure ones...</p>