AT Protocol

Last updated
AT Protocol
Communication protocol
AT Protocol Logo.svg
Bluesky-AT Protocol federation architecture.svg
A diagram of the AT Protocol federation architecture as of October 2024.
AbbreviationATProto
Purpose Decentralized social networking
Developer(s) Bluesky Social, PBC
IntroductionOctober 18, 2022;2 years ago (2022-10-18)
Port(s) 80, 443
Website atproto.com

The AT Protocol (Authenticated Transfer Protocol, pronounced "at-protocol" and commonly shortened to ATProto) [1] [2] is a protocol and open standard for decentralized social networking services. [3] It is under development by Bluesky Social PBC, a public benefit corporation originally created as an independent research group within Twitter to investigate the possibility of decentralizing the service. [4]

Contents

The AT Protocol aims to address perceived issues with other decentralized protocols, such as user experience, platform interoperability, discoverability, network scalability, and portability of user data and social graphs. [3] It employs a modular microservice architecture and a federated, server-agnostic user identity to enable movement between protocol services, with the goal of providing an integrated online experience. [5] Platforms can access and serve any user content within the network by fetching content formatted as predefined data schemas from federated network-wide data streams. [6] [7]

The AT Protocol powers the Bluesky social network, which was created as a proof of concept for the protocol, and is the main service in an ecosystem of platforms and services built on the AT Protocol referred to as the ATmosphere. [8] [9] [10] Bluesky Social has pledged to transfer the protocol's development to a standards body such as the Internet Engineering Task Force (IETF) in the near future. [11]

Design

The AT Protocol aims to create a decentralized, interoperable, and scalable online ecosystem where users can retain, manage, and customize a single federated online identity across various online platforms and services. Bluesky Social describes the protocol as being "modeled after the open web itself". [5]

Compared to other protocols for social networking such as ActivityPub, where implementations are typically designed as a monolithic server that hosts both user data and the application, it splits up these elements into smaller microservices, which can be used as needed. [12]

AT Protocol clients and services interoperate through an HTTP API called XRPC that primarily uses JSON for data serialization. [13] Additionally, all data within the protocol that must be authenticated, referenced, or stored is encoded in CBOR. [14]

User identity

The AT Protocol utilizes a dual identifier system: a mutable domain name handle and an immutable decentralized identifier (DID). Handles serve as user-end identifiers and are verified by querying a domain's resource records. DIDs resolve to DID documents, which contain references to key user metadata, such as the user's handle, public keys, and data repository. [15]

AT Protocol's identity infrastructure. AT Protocol Identity Architecture.svg
AT Protocol's identity infrastructure.

Services can assign handles to new users upon signup using subdomains (e.g. @username.bsky.social). Alternatively, users can set a custom domain or subdomain as their handle (e.g. @username.com or @username.wikipedia.org) by adding a TXT record to the domain's records or by responding a HTTP requests to a specific .well-known URL, associating the domain or subdomain to the user's DID. [16] [17]

The protocol's dual identifier system provides both user-friendly identifiers for use in end-user services and consistent cryptographic identities within the protocol, while also providing a robust TCP/IP-based account verification mechanism at the protocol level.

User data repositories

User data within the protocol is stored in dedicated data repositories, or "repos". Each user is associated with a single repository, over which they have exclusive management rights. Repositories contain mutable collections of user records, which log actions such as posts, likes, follows, and blocks. Records are persistent and can only be added or removed at the explicit request of the user. [18]

Each record within a repository's collection is assigned a unique record key, which is used by network agents to reference records within a user's repository. The current implementation of record keys is the timestamp identifier (TID), derived from the record's creation time. [19] Repositories store collections in a Merkle search tree, which sorts records chronologically based on their TID. [20]

Media files, along with their metadata, size, and media type, are stored separately from repositories as blobs, a type of unstructured binary data, in the user's host server. [21] This allows network agents to access and process arbitrary media files regardless of their original schema or upload context. [22]

Personal Data Servers

Personal Data Servers (PDSes) host user repositories and their associated media. They also serve as the network access point for users, facilitating repository updates, backups, data queries, and user requests. [5]

Platform clients access the protocol on the user's behalf by querying their PDS, which, in turn, fetches the requested data from other services within the network. This design differs from ActivityPub, where protocol interactions and services are handled by monolithic host servers. Since network events are resolved through the protocol's network-wide indexing infrastructure, the availability of any single PDS is, by design, potentially inconsequential to the user experience. [23]

The AT Protocol prioritizes data portability, enabling users to back up and migrate repositories and associated media without data loss, even in the event of an adversarial PDS. [24] The design of PDSes within the protocol results in low computational requirements for operation, allowing individuals or groups to run their own PDSes without the need for significant computational resources. [3]

Although most users' repositories reside in PDSes run by Bluesky Social, many independent PDSes exist within the network. [2]

Relays and the firehose

Relays are a key component of the protocol's indexing infrastructure, serving as the core indexers within the network. [5] Relays crawl the network by continuously fetching repository updates from PDSes before aggregating, indexing, and forwarding these updates into network-wide data streams, collectively called the firehose. [7] The firehose is available to all network agents, and can be consumed by any service within the network. [3] Relays can choose to index all or part of the network. [5]

By eliminating the need to crawl or store user data and providing a unified data stream, relays simplify the development of applications and services in the protocol and reduce their operational costs. [25]

Relays have been criticized as being the most centralized component in the protocol's design, given their near-indispensable role in the network and a lack of clear incentives for running a relay. [26] [27]

App Views

App Views, analogous to current-day social networking services, are end-user platforms and services within the protocol that consume, process, and deliver data from the relay to user clients in response to queries from users' PDSes. They utilize network-wide information from the firehose, such as posts, likes, follows, and replies, to create customized user experiences within their clients. [3]

The design of App Views within the protocol allows for significant variation in implementation. App Views can implement invite systems, custom algorithms, alternative clients, varying monetization and content moderation strategies, and off-protocol services. [28] Despite these differences, all App Views operate from the same data sourced from the firehose. This architecture reduces the computational load and storage requirements of App Views, and prevents user lock-in by enabling users to easily switch between App Views while retaining their posts, follows, likes, etc. [29]

The largest App View on the protocol is currently Bluesky, although other App Views, such as WhiteWind (a long-form blogging platform), Frontpage (a Hacker News-style social news website) and Smoke Signal (an RSVP management service) are also available within the protocol. [30] [31] [32]

Lexicons

All posts within the AT Protocol follow a specific global schema language called a lexicon to support different service and platform modalities. [33] App Views within the protocol have the flexibility to define their own unique lexicons, or utilize existing ones.

This approach allows App Views to create custom lexicons that are tailored to their specific use case while maintaining compatibility with the broader network. As an example, records displayed in an App View focused on microblogging would likely use a different lexicon than one focused on video-sharing, as their content types require different sets of attributes.

However, App Views can also choose to serve content using lexicons defined by other App Views, even if the content was originally posted elsewhere in the network. [6] For example, a new microblogging App View could choose to serve previously posted content using the lexicon defined by an established competitor, enabling them to provide novel features and services while maintaining compatibility with existing content.

This schema design is intended to eliminate user lock-in and foster user-centric innovation by forcing App Views to differentiate themselves through unique user experiences and additional functionality, rather than relying on exclusive access to content. [34]

Lexicons are referenced within records using Namespaced Identifiers (NSIDs), which consist of a domain authority in reverse domain-name order, followed by an arbitrary name segment. [35] For example, com.appview.foo is a valid NSID, where com.appview is the domain authority, and foo is the name segment.

The most popular lexicon in the protocol, app.bsky, defines Bluesky's microblogging schema. [6]

Opinionated services

Opinionated services are services within the protocol that process data from the firehose to provide subjective judgements on network data for the purposes of content moderation and curation. These services contrast with the intended "unopinionated" nature of relays and App Views. [3] Opinionated services enable users to customize their content consumption and moderation preferences within the protocol while maintaining the neutrality of the protocol's core components.

Users have the ability to subscribe and unsubscribe to these services at any time through their client app (unless they are hard-coded into the user's current App View.) [28] The modularity of these services allows for a customizable, stackable, user-centric approach to content curation and moderation within the protocol. [36]

Labelers

Labelers produce judgements about user-generated content, such as identifying spam or inappropriate material. These labels can be applied to various aspects of the network, including posts, images, or accounts. The output of labelers is consumed by App Views and PDSes, which can then provide various strategies to users for handling labeled content, such as hiding, labeling, or blurring. [37]

Bluesky Social has open-sourced its internal labeler moderation service "Ozone", allowing users to create custom moderation services for the network. [38] [36]

Although labelers can be used as a moderation service, they can also serve informational or entertainment purposes, such as labeling post topics, user pronouns, or adding positive or playful labels to user profiles and posts. [39]

Feed generators

Feed generators process posts within the firehose for inclusion in custom feeds. After a PDS query, they return a list of post IDs to the user's App View, which can then be used to create curated feeds. [40] [41]

Adoption

The protocol's reference implementation was first released to GitHub on May 4, 2022 under the name Authenticated Data Experiment (ADX), and is licensed under both the MIT and Apache licenses. [42] It rebranded to the AT Protocol in October 2022. [43]

The AT Protocol has been adopted for use by the Bluesky social network (also developed by Bluesky Social PBC), and is its most popular implementation. The social network itself opened federation with other Personal Data Servers in late February 2024, as it had launched without the ability to federate with other servers not run by Bluesky Social. [44] Additionally, the news aggregator Flipboard allows users to login with their Bluesky account to view and interact with posts from the service. [45] To aid adoption, Bluesky Social funds various projects that use the AT Protocol for federating and/or creating content via grants. [46] A notable application funded by the grants is a proxy server known as SkyBridge, which can convert API calls from Mastodon apps to their equivalent AT Protocol/Bluesky APIs, allowing users to have access to both networks even without official support. [47]

While the AT Protocol is a separate protocol with no major technical similarities to other protocols, there have been services developed that can bridge content across protocols. An example is the Bridgy Fed software, which can crosspost content between ActivityPub and the AT Protocol. [48] [49] Posts from Nostr can also be "double-bridged" to the AT Protocol via another bridge that can crosspost notes from Nostr to ActivityPub. [50]

Criticism

According to Christine Lemmer-Webber, co-author of the ActivityPub protocol and of an early internal proposal for an architecture eventually not adopted by Bluesky Social, "Bluesky is not meaningfully decentralized and that it is certainly not federated according to any technical definition of federation we have had in a decentralized social network context previously. However, 'credible exit' is a reasonable term to describe what Bluesky is aiming for". [51]

See also

Related Research Articles

Microblogging is a form of blogging using short posts without titles known as microposts. Microblogs "allow users to exchange small elements of content such as short sentences, individual images, or video links", which may be the major reason for their popularity. Some popular social networks such as X (Twitter), Threads, Tumblr, Mastodon, Bluesky and Instagram can be viewed as collections of microblogs.

The Facebook Platform is the set of services, tools, and products provided by the social networking service Facebook for third-party developers to create their own applications and services that access data in Facebook.

<span class="mw-page-title-main">GNU social</span> Microblogging social networking service

GNU social is a free and open-source microblogging social networking service that implements the OStatus and ActivityPub standards for interoperability between installations. While offering similar functionality to social networks such as Twitter, GNU social seeks to provide the ability for open and federated communication between different microblogging communities, known as 'instances'. Both enterprises and individuals can install and control their own instances and user data.

<span class="mw-page-title-main">Distributed Social Networking Protocol</span>

The Distributed Social Networking Protocol (DSNP) is an open-source social media protocol designed to decentralize data ownership, allow easier cross-platform interaction, and let users regain control over their personal data. This includes posts, connections, and messages. The decentralized approach allows users to retain ownership of their information and move it between platforms without relying on a single provider.

<span class="mw-page-title-main">Friendica</span> Free software for distributed social networks

Friendica is a free and open-source software distributed social network. It forms one part of the Fediverse, an interconnected and decentralized network of independently operated servers.

Distributed social network projects generally develop software, protocols, or both.

pump.io Decentralized social network and protocol

pump.io is a software package containing a social networking service and communication protocol that can be used as a federated social network. Started by Evan Prodromou, it is a follow-up to his previous microblogging software StatusNet and its OStatus protocol. It is designed to be more lightweight and usable for general activity streams instead of the predecessor's focus on microblogging timelines, with its goal being to achieve "most of what people want from a social network".

<span class="mw-page-title-main">InterPlanetary File System</span> Content-addressable, peer-to-peer hypermedia distribution protocol

The InterPlanetary File System (IPFS) is a protocol, hypermedia and file sharing peer-to-peer network for storing and sharing data in a distributed hash table. By using content addressing, IPFS uniquely identifies each file in a global namespace that connects IPFS hosts, creating a resilient system of file storage and sharing.

<span class="mw-page-title-main">Well-known URI</span>

A well-known URI is a Uniform Resource Identifier for URL path prefixes that start with /.well-known/. They are implemented in webservers so that requests to the servers for well-known services or information are available at URLs consistent well-known locations across servers.

<span class="mw-page-title-main">Mastodon (social network)</span> Open source, self-hosted, social media service

Mastodon is an open source, self-hosted, social networking service. Mastodon uses the ActivityPub protocol for federation which allows users to communicate between independent Mastodon instances and other ActivityPub compatible services. Mastodon has microblogging features similar to Twitter, and is generally considered to be a part of the Fediverse.

<span class="mw-page-title-main">Fediverse</span> Network of federated social media platforms

The Fediverse is a collection of social networking services that can communicate with each other using a common protocol. Users of different websites can send and receive status updates, multimedia files and other data across the network. The term Fediverse is a portmanteau of "federation" and "universe".

<span class="mw-page-title-main">ActivityPub</span> Decentralized social networking protocol

ActivityPub is a protocol and open standard for decentralized social networking. It provides a client-to-server API for creating and modifying content, as well as a federated server-to-server (S2S) protocol for delivering notifications and content to other servers. ActivityPub has become the main standard used in the fediverse, a popular network used for social networking that consists of software such as Mastodon, Pixelfed and PeerTube.

Secure Scuttlebutt (SSB) is a peer-to peer communication protocol, mesh network, and self-hosted social media ecosystem. Each user hosts their own content and the content of the peers they follow, which provides fault tolerance and eventual consistency. Messages are digitally signed and added to an append-only list of messages published by an author. SSB is primarily used for implementing distributed social networks, and utilizes cryptography to assure that content remains unforged as it is propagated through the network.

MeWe is a global social media and social networking service. As a company based in Los Angeles, California it is also known as Sgrouples, Inc., doing business as MeWe. The site has been described as a Facebook alternative due to its focus on data privacy.

<span class="mw-page-title-main">Pleroma (software)</span> Self-hosted social networking software

Pleroma is a free and open-source microblogging social networking service. Unlike popular microblogging services such as Twitter or Weibo, Pleroma can be self-hosted and operated by anyone with a server and a web domain, a combination commonly referred to as an instance. Instance administrators can manage their own code of conduct, terms of service, and content moderation policies, allowing users to have more control over the content they view as well as their experience. It was named after the religious concept of pleroma, or the totality of divine powers.

<span class="mw-page-title-main">Pixelfed</span> Open source photo-sharing platform

Pixelfed is a free and open-source image sharing social network service. The platform uses a decentralized architecture which is roughly comparable to e-mail providers, meaning user data is not stored on one central server. It uses the ActivityPub protocol, allowing users to interact with other social networks within the protocol, such as Mastodon, PeerTube, and Friendica. Pixelfed and other platforms utilizing this protocol are considered to be part of the Fediverse.

<span class="mw-page-title-main">Odysee</span> Decentralized video hosting platform

Odysee is an American decentralized video hosting platform built on the LBRY blockchain. It positions itself as an alternative to mainstream services like YouTube, but with a focus on free speech and decentralization.

<span class="mw-page-title-main">Bluesky</span> Social media service

Bluesky is a microblogging social media service. Similar to Twitter, users can share short text messages, images, and videos in short posts colloquially known as "skeets". It is owned by Bluesky Social PBC, a public benefit corporation based in the United States.

<span class="mw-page-title-main">Nostr</span> Decentralized social networking protocol

Nostr is an open protocol for decentralized message transmission, with the intention to be able to resist internet censorship while maintaining session integrity. The protocol achieves decentralization through users publishing content via a cryptographic key pair to various "relays", a WebSocket server which produces an activity stream of received content from users that subscribe to it. This allows the network to verify users and achieve account portability on Nostr, as users have to sign all posts using their key pair to utilize its identity. This requires users maintaining personal copies of their keys to have complete control over its identity, however services using Nostr can "remember" a private key for repeated use.

<span class="mw-page-title-main">Misskey</span> Open source, federated, social networking service

Misskey is an open source, federated, social networking service created in 2014 by Japanese software engineer Eiji "syuilo" Shinoda. Misskey uses the ActivityPub protocol for federation, allowing users to interact between independent Misskey instances, and other ActivityPub compatible platforms. Misskey is generally considered to be part of the Fediverse.

References

  1. ↑ "The AT Protocol". Bluesky. Retrieved 2024-07-30.
  2. 1 2 "2024 Protocol Roadmap | Bluesky". docs.bsky.app. 2024-05-06. Retrieved 2024-09-05.
  3. 1 2 3 4 5 6 Kleppmann, Martin; Frazee, Paul; Gold, Jake; Graber, Jay; Holmgren, Daniel; Ivy, Devin; Johnson, Jeromy; Newbold, Bryan; Volpert, Jaz (2024-02-05), Bluesky and the AT Protocol: Usable Decentralized Social Media, arXiv: 2402.03239
  4. ↑ Robertson, Adi (2022-10-29). "Will Elon Musk keep funding Twitter's most interesting side project?". The Verge. Retrieved 2024-07-31.
  5. 1 2 3 4 5 "Federation Architecture | Bluesky". docs.bsky.app. Retrieved 2024-09-05.
  6. 1 2 3 "Lexicon | AT Protocol". atproto.com. Retrieved 2024-09-05.
  7. 1 2 "Firehose | Bluesky". docs.bsky.app. Retrieved 2024-09-05.
  8. ↑ "Glossary of terms". AT Protocol. Retrieved 2024-09-10.
  9. ↑ Robertson, Adi (2019-12-11). "Twitter is funding research into a decentralized version of its platform". The Verge. Retrieved 2024-07-30.
  10. ↑ Conger, Kate (2022-03-02). "Twitter Wants to Reinvent Itself, by Merging the Old With the New". The New York Times. ISSN   0362-4331 . Retrieved 2024-07-31.
  11. ↑ Patel, Nilay (2024-03-25). "Bluesky CEO Jay Graber on breaking free from Twitter and competing with Threads and Mastodon". The Verge. Retrieved 2024-08-04.
  12. ↑ "ATProto for distributed systems engineers". atproto.com. 2024-09-03.
  13. ↑ "HTTP API (XRPC) | AT Protocol". atproto.com. Retrieved 2024-09-05.
  14. ↑ "Data Model - Protocol API Reference". atproto.com. Retrieved 2024-09-06.
  15. ↑ "Identity | AT Protocol". atproto.com. Retrieved 2024-09-05.
  16. ↑ "Domain Names as Handles in Bluesky". Bluesky. Retrieved 2024-09-05.
  17. ↑ "How to verify your Bluesky account". Bluesky. Retrieved 2024-11-26.
  18. ↑ "Personal Data Repositories | AT Protocol". atproto.com. Retrieved 2024-09-05.
  19. ↑ "Record Key - Protocol API Reference". atproto.com. Retrieved 2024-09-06.
  20. ↑ "Repository - Protocol API Reference". atproto.com. Retrieved 2024-09-06.
  21. ↑ "Protocol API Reference". atproto.com. Retrieved 2024-09-06.
  22. ↑ "HTTP API (XRPC) - Protocol API Reference". atproto.com. Retrieved 2024-09-06.
  23. ↑ "PDS Entryway | Bluesky". docs.bsky.app. Retrieved 2024-09-05.
  24. ↑ "Repository | AT Protocol". atproto.com. Retrieved 2024-09-05.
  25. ↑ "The AT Protocol Developer Ecosystem". Bluesky. Retrieved 2024-09-05.
  26. ↑ "AT Protocol - First Thoughts - Rusted Gears - Obsidian Publish". publish.obsidian.md. Retrieved 2024-09-05.
  27. ↑ Schulman, Rory Mir and Ross (2024-06-18). "What's the Difference Between Mastodon, Bluesky, and Threads?". Electronic Frontier Foundation. Retrieved 2024-09-05.
  28. 1 2 "Moderation in a Public Commons". Bluesky. Retrieved 2024-09-05.
  29. ↑ "What is Bluesky?". Bluesky. Retrieved 2024-09-05.
  30. ↑ "WhiteWind atproto blog | WhiteWind blog". whtwnd.com. Retrieved 2024-09-05.
  31. ↑ "Why atprotocol? | Smoke Signal". docs.smokesignal.events. Retrieved 2024-09-05.
  32. ↑ Hof, Laurens (2024-07-04). "Last Month in Bluesky – June 2024". fediversereport.com. Retrieved 2024-09-06.
  33. ↑ "Protocol Overview | AT Protocol". atproto.com. Retrieved 2024-09-05.
  34. ↑ "Bluesky: An Open Social Web". Bluesky. Retrieved 2024-09-05.
  35. ↑ "Namespaced Identifiers (NSIDs) - Protocol API Reference". atproto.com. Retrieved 2024-09-06.
  36. 1 2 "Bluesky's Stackable Approach to Moderation". Bluesky. Retrieved 2024-09-05.
  37. ↑ "Labeling and Moderation Controls". GitHub. Retrieved 2024-09-05.
  38. ↑ Ozone: labeling service for Bluesky and other atproto apps, bluesky-social, 2024-09-05, retrieved 2024-09-06
  39. ↑ "Labeling and Moderation Controls". GitHub. Retrieved 2024-09-06.
  40. ↑ "Custom Feeds | Bluesky". docs.bsky.app. Retrieved 2024-09-05.
  41. ↑ ATProto Feed Generator, bluesky-social, 2024-09-05, retrieved 2024-09-06
  42. ↑ Robertson, Adi (2022-05-04). "Twitter's decentralized, open-source offshoot just released its first code". The Verge. Retrieved 2024-07-31.
  43. ↑ Pierce, David (2022-10-19). "Bluesky built a decentralized protocol for Twitter — and is working on an app that uses it". The Verge. Retrieved 2024-08-04.
  44. ↑ Khalid, Amrita (2024-02-22). "Bluesky starts letting users host their own servers". The Verge. Retrieved 2024-08-04.
  45. ↑ Davis, Wes (2023-05-23). "Flipboard is ready to work with Bluesky and Pixelfed". The Verge. Retrieved 2024-08-01.
  46. ↑ Perez, Sarah (2024-03-11). "Bluesky is funding developer projects to give its Twitter/X alternative a boost". TechCrunch. Retrieved 2024-08-01.
  47. ↑ Perez, Sarah (2024-04-25). "Bluesky backs a project that would let Mastodon apps, like Ivory, work with its network". TechCrunch. Retrieved 2024-08-09.
  48. ↑ Perez, Sarah (2024-06-05). "Bluesky and Mastodon users can now talk to each other with Bridgy Fed". TechCrunch. Retrieved 2024-08-04.
  49. ↑ Silberling, Amanda (2024-02-14). "Bluesky and Mastodon users are having a fight that could shape the next generation of social media". TechCrunch. Retrieved 2024-08-04.
  50. ↑ Perez, Sarah (2024-05-21). "The 'vote Trump' spam that hit Bluesky in May came from decentralized rival Nostr". TechCrunch. Retrieved 2024-08-04.
  51. ↑ "How decentralized is Bluesky really?" Christine Lemmer-Webber 22 November 2024 https://dustycloud.org/blog/how-decentralized-is-bluesky/

Further reading

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.