title: Shared encrypted file but using different key to decrypt
body: <p>I just curious, if there any encryption algorithm that can support this scenario.</p>
  
  <p>A plain text file (T) was shared among two parties, this file was encrypted (let say symmetric AES) to become encrypted file (E). The Encrypted file will be stored in the server, and after encryption takes place, additional party can be added at any time. </p>
  
  <p>When first party wants to get the T file, he/she passes P1K to decrypt E file
  when second party wants to get the T file, he/she passed P2K to decrypt E file.</p>
  
  <p>Any idea how to achieve this using pure encryption algorithm only (without using database to store intermediary key) ?</p>