Can I play Encrypted Movie File

Question

I'm developing a mobile app with a full movie, and I want this movie to be encrypted so that they wont copy my movie. I got problem with decryption cause some mobile don't have enough memory and gets some lags

My question is can I play my movie even its still encrypted and without doing some decryption?

Answer 1

You cannot play the encrypted video (that's the point of the encryption after all), but you can instead only decrypt and hold in memory the part of the movie that the playback library needs to access in this moment. There are block cipher modes like CTR that allow you to decrypt the stream at arbitrary positions so you can even seek in the video playback.

Be warned though that if your application can decrypt the video then the key has to be accessible to it somehow and is thus accessible to a dedicated attacker analyzing and possible reverse engineering your program. In the end there is no secure DRM scheme.