| LICENSE.txt | ||
| README.org | ||
OcapPub: Towards networks of consent
- Conceptual overview
- Key concepts
- Limitations
- Future work
- Conclusions
This paper released under the Apache License version 2.0; see LICENSE.txt for details.
For a broader overview of various anti-spam techniques, see AP Unwanted Messages, which is in many ways informed this document but currently differs in some implementation rollout differs. (These two documents may converge.)
Conceptual overview
ActivityPub
ActivityPub is a federated social network protocol. It is generally fairly easily understood by reading the Overview section of the standard. In short, just as anyone can host their own email server, anyone can host their own ActivityPub server, and yet different users on different servers can interact. At the time of writing, ActivityPub is seeing major uptake, with several thousand nodes and several million registered users (with the caveat that registered users is not the same as active users). The wider network of ActivityPub-using programs is often called "the fediverse" (though this term predates ActivityPub, and was also used to describe adoption of its predecessor, OStatus).
ActivityPub defines both a client-to-server and server-to-server protocol, but at this time the server-to-server protocol is what is most popular and is the primary concern of this article.
ActivityPub's core design is fairly clean, following the actor model. Different entities on the network can create other actors/objects (such as someone writing a note) and communicate via message passing. A core set of behaviors are defined in the spec for common message types, but the system is extensible so that implementations may define new terms with minimal ambiguity. If two instances both understand the same terms, they may be able to operate using behaviors not defined in the original protocol. This is called an "open world assumption" and is necessary for a protocol as general as ActivityPub; it would be extremely egotistical of the ActivityPub authors to assume that we could predict all future needs of users.1
Unfortunately (mostly due to time constraints and lack of consensus), even though most of what is defined in ActivityPub is fairly clean/simple, ActivityPub needed to be released with "holes in the spec". Certain key aspects critical to a functioning ActivityPub server are not specified:
- Authentication is not specified. Authentication is important to verify "did this entity really say this thing".2 However, the community has mostly converged on using HTTP Signatures to sign requests when delivering posts to other users. The advantage of HTTP Signatures is that they are extremely simple to implement and require no normalization of message structure; simply sign the body (and some headers) as-you-are-sending-it. The disadvantage of HTTP Signatures is that this signature does not "stick" to the original post and so cannot be "carried around" the network. A minority of implementations have implemented some early versions of Linked Data Proofs (formerly known as "Lined Data Signatures"), however this requires access to a normalization algorithm that not all users have a library for in their language, so Linked Data Proofs have not as of yet caught on as popularly as HTTP Signatures.
- Authorization is also not specified. (Authentication and authorization are frequently confused (especially because in English, the words are so similar) but mean two very different things: the former is checking who said/did a thing, the latter is checking whether they are allowed to do a thing.) As of right now, authorization tends to be extremely ad-hoc in ActivityPub systems, sometimes as ad-hoc as unspecified heuristics from tracking who received messages previously, who sent a message the first time, and so on. The primary way this is worked around is sadly that interactions which require richer authorization simply have not been rolled out onto the ActivityPub network.
Compounding this situation is the general confusion/belief that autorization must stem from authentication. This document aims to show that not only is this not true, it is also a dangerous assumption with unintended consequences. An alternative approach based on "object capabilities" is demonstrated, showing that the actor model itself, if we take it at its purest form, is itself already a sufficient authorization system.
Unfortunately there is a complication.
At the last minute of ActivityPub's standardization, sharedInbox was
added as a form of mutated behavior from the previously described
publicInbox (which was a place for servers to share public content).
The motivation of sharedInbox is admirable: while ActivityPub is based
on explicit message sending to actors' inbox endpoints, if an actor
on server A needs to send a message to 1000 followers on server B,
why should server A make 1000 separate requests when it could do it
in one?
A good point, but the primary mistake in how this one request is made;
rather than sending one message with a listing of all 1000 recipients
on that server (which would preserve the actor model integrity),
it was advocated that servers are already tracking follower information,
so the receiving server can decide whom to send the message to.
Unfortunately this decision breaks the actor model and also our suggested
solution to authorization; see MultiBox for a suggestion on how we
can solve this.
Despite these issues, ActivityPub has achieved major adoption. ActivityPub has the good fortune that its earliest adopters tended to be people who cared about human rights and the needs of marginalized groups, and spam has been relatively minimal.
The mess we're in
Mastodon Is Like Twitter Without Nazis, So Why Are We Not Using It? – Article by Sarah Jeong, which drove much interest in adoption of Mastodon and the surrounding "fediverse"
At the time this article was written about Mastodon (by far the most popular implementation of ActivityPub, and also largely responsible for driving interest in the protocol amongst other projects), its premise was semi-true; while it wasn't that there were no neo-nazis on the fediverse, the primary group which had driven recent adoption were themselves marginalized groups who felt betrayed by ther larger centralized social networks. They decided it was time for them to make homes for themselves. The article participated in an ongoing narrative that (from the author's perspective) helped reinforce these community norms for the better.
However, there nothing about Mastodon or the fediverse at large (including the core of ActivityPub) specifically prevented nazis or other entities conveying undesirable messages (including spam) from entering the network; they just weren't there or were in small enough numbers that instance administrators could block them. However, the fediverse no longer has the luxury of claiming to be neo-nazi free (if it ever could). The risk that people from marginalized groups, which the fediverse has in recent history appealed to, are now at risk from targeted harassment from these groups. Even untargeted messages, such as general hate speech, may have a severe negative impact on one's well being. Spam, likewise, is an increasing topic of administrators and implementors (as it has historically been for other federated social protocols, such as email/SMTP and OStatus during its heyday). It appears that the same nature of decentralized social networks in allowing marginalized communities to make communities for themselves also means that harassment, hate speech, and spam are not possible to wholly eject from the system.
Must all good things come to an end?
Unwanted messages, from spam to harassment
One thing that spam and harassment have in common is that they are the delivery of messages that are not desired by their recipient. However, it would be a mistake to claim that the impact of the two are the same: spam is an annoyance, and mostly wastes time. Harassment wastes time, but may also cause trauma.
Nonetheless, despite the impact of spam and harassment being very different, the solutions are likely very similar. Unwanted messages tend to come from unwanted social connections. If the problem is users receiving unwanted messages, perhaps the solution comes in making intentional social connections. But how can we get from here to there?
Did we borrow the wrong assumptions?
"What if we're making the wrong assumptions about our social networks? What if we're focusing on breadth, when we really should be focusing on depth?" – from a conversation with Evan Prodromou, initial designer of both ActivityPub and OStatus' protcol designs
Freedom of speech also means freedom to filter
Don't pretend we can prevent what we can't
Anti-solutions
(Note that things in the anti-solutions category aren't necessarily "things that aren't useful", but rather "things that end up causing problems if they're the foundation".)
Blocklists, allow-lists, and perimeter security
Access Control Lists
Content-centric filtering
Reputation scoring
Going back to centralization
A way forward: networks of consent
Must we boil the ocean?
Key concepts
Object capabilities (ocaps)
Ocaps meet ActivityPub objects/actors
True names, public profiles, private profiles
Accountability and revocation in an ocap system
Rights amplification and group-style permissions
multiBox vs sharedInbox
Limitations
Future work
Petnames
Conclusions
The technology that ActivityPub uses to accomplish this is called json-ld and admittedly has been one of the most controvercial decisions in the ActivityPub specification. Most of the objections have surrounded the unavailability of json-ld libraries in some languages or the difficulty of mapping an open-world assumption onto strongly typed systems without an "other data" bucket. Since a project like ActivityPub must allow for the possibility of extensions, we cannot escape open-world assumptions. However, there may be things that can be done to improve happiness about what extension mechanism is used; these discussions are out of scope for this particular document, however.
Or more accurately, since users may appoint someone else to manage posting for them, "was this post really made by someone who is authorized to speak on behalf of this entity".