title: How to change git-crypt key
body: <p>I forked a repo using <a href="https://github.com/AGWA/git-crypt/" rel="nofollow noreferrer">git-crypt</a> and I need to update the git-crypt key so that the upstream git-crypt key can't decrypt the new repo.</p>
  
  <p>The <code>git-crypt help</code> documentation and <a href="https://github.com/AGWA/git-crypt/blob/master/README.md" rel="nofollow noreferrer">README</a> don't appear to explain how to change a git-crypt key.</p>
  
  <p>I tried various ways of wiping the git-crypt config and re-initializing.  Unfortunately, all attempts at doing so seem to break various things like git diff showing errors like <code>smudge filter git-crypt failed</code>.  Some of this behavior is documented at <a href="https://github.com/AGWA/git-crypt/issues/78" rel="nofollow noreferrer">Running <code>git-crypt init</code> on an already initialized repository renders the data unreadable</a>.  None of the suggestions in the comments at <a href="https://github.com/AGWA/git-crypt/issues/47" rel="nofollow noreferrer">https://github.com/AGWA/git-crypt/issues/47</a> prevent the git diff fatal errors. (I am fine with git diff showing useless output from unencrypted binary file history, but it is <em>not</em> ok for <code>git diff</code> across some commits to give fatal errors preventing diffing even non-encrypted files.)</p>
  
  <p>This seems like a major requirement of git-crypt, so I can't believe this isn't supported, e.g. if you need to rotate a git-crypt key because someone leaves a company.</p>