Here Star Student Project give some limitation to the receiver; they are only downloading the file or having read only permission from the cloud, because they didn’t know the private key for this file. And there is possible to do a forgery operation by the receiver with the help of cloud public key.
https://www.blogger.com/blogger.g?blogID=8455578136612679850#editor/target=post;postID=7856665667426268842