I was wondering if there is a smart way for a user to only encrypt a subset of a plaintext.
I'll try to be more specific. Let's suppose the user U wants to use a special cipher such that given a plaintext P and some additional information, it only encrypts the subset requested by the user, the rest of the plaintext is not modified.
Does it exist such a cipher? If so, where can I find it and how does it work? If not, how would you do design such a cipher?
EDIT: I've read about selective encryption but it looks like it's mainly meant for images and video streams