title: Encrypt an existing zip file
body: <p>I have an existing zip file, I want to use AESManaged class to encrypt it, but I don't find where I can set the password to the zip file in that class. After researching, I found some libaries such as 'DotNetZip' can complete the task. But my file is already a .zip, I needn't to compress again, I only want to encrypt it. Anyone can help me to use AESManaged class to ahieve the purpose?</p>
  
  <p>Thanks</p>