title: Use existing PEM private key to sign data on iOS
body: <p>I need to import an existing key into my app to use it with RSA encryption, I don't want to generate a new key.
  I've read the apple documentation <a href="http://developer.apple.com/library/ios/#documentation/Security/Conceptual/CertKeyTrustProgGuide/iPhone_Tasks/iPhone_Tasks.html" rel="nofollow">http://developer.apple.com/library/ios/#documentation/Security/Conceptual/CertKeyTrustProgGuide/iPhone_Tasks/iPhone_Tasks.html</a>
  But it doesn't seem to provide a way to import an existing PEM private key, it talks about creating them, but not about how to use an existing key.</p>
  
  <p>Is this actually possible? Are there any API or Lib to do this? I don't need this for appstore, so don't be shy with responses if they are against the appstore rules.</p>