Who’s allowed to reply to your posts?
Truthfully, anyone who can see it (and nothing can prevent someone who wants to from seeing something you make public). If they have to, they can link, copy and paste or screenshot it, and fundamentally there’s no way of stopping them.
But that’s not really what we’re talking about when we talk about replies on social network’s. What we’re really talking about is who’s replies get to show up under your post; or, in other words, who gets to borrow your audience.
The Fediverse has a bit of a moderation problem. In fact, it’s had one for quite a while.
When I wrote the first draft of the ActivityPump spec back in 2014, it had an Authorization section which began like this:
Authorization This is a stub, to be expanded. OAuth 2.0 is an open question.
ActivityPump uses authorization for two purposes; first, to authenticate clients to servers, and secondly in federated implementations to authenticate servers to each other.
History For the past few decades, the block cipher has been the primary symmetric cryptographic primitive. Aside from the odd stream cipher (primarily RC-4), pretty much every common cryptographic primitive from before 2010 can be seen as built from a block cipher.
Quick note: How do we define a block cipher? A block cipher is a function with the form c = f(p, k) where c, p are an N-bit ciphertext and plaintext respectively, and k is an M-bit key.