Revocable File Sharing?
swolchok: The general consensus is that DRM cannot be made secure. Why? You are delivering content and the means of playing it to the user. If the user can play it, the user can copy it. Game over.However, if the recipient of the shared document is also interested in the timed destruction of the document, you could encrypt the document and escrow the key on a web server. The host of the web server promises to erase the key after a certain time, and the recipient promises to delete all unencrypted copies of the document and temporary encryption keys.What I have just described above is a much simpler way to implement Vanish (http://vanish.cs.washington.edu/) if you allow the use of a trusted web server. Note that the full Vanish implementation is insecure (http://z.cs.utexas.edu/users/osa/unvanish/papers/vanish-brok...).