What is the the point of an "online" mode for an authenticated cipher?
I understand what "online" means in this context. However, I have trouble coming up with applications that would benefit from such a feature.
Usually, the "messages" that are encrypted and authenticated are not too long and I think that this is due to people not wanting to decrypt "big messages" completely only to throw them away if the tag is finally invalid. So, at least for network protocols, it seems like a very good idea to insert authentication tags more frequently.
But this strategy makes the "online" feature of some AE implementation seem irrelevant especially since support for online modes makes the implementation more complicated.