What does Authenticated Transfer protocol mean?

Authenticated Transfer (AT) protocol is an open and decentralized standard for social media. AT is being developed by Bluesky, and it will help developers build social apps that safeguard users’ data and privacy while increasing account portability across servers.

Bluesky was started as a project at Twitter in 2019. In 2022, it was established as an independent company after receiving $13 million in funding. The former Twitter CEO and co-founder Jack Dorsey is a board member. 

The company is also developing Bluesky Social, a decentralized social app that runs on the AT protocol. Private beta testing is now underway; you can join the waitlist here. 

A “working in public” approach

Bluesky had introduced the first iteration of AT, ADX, in May 2022. Since then, code improvements and simplifications have been introduced into the protocol, and it’s renamed to the Authenticated Transfer (AT). The team follows a “working in public” approach and shares regular updates. Earlier, they also shared details of the intermediate steps of protocol development by releasing the code and architecture overview. 

Bluesky’s long-term target is to realize global social networking at scale. AT protocol will underpin all related developments. 

AT deploys a new federated social network. 

A federated network is a set of linked networks that agree upon operation standards collectively, where different parties can transfer data and messages from one network to another. A popular federated protocol network is ActivityPub used by Mastodon. Another is Matrix. 

Although other protocols already exist, why did Bluesky choose to build a separate protocol?

Account portability

In a blog post, the company refers to “account portability” as the main reason for building the AT protocol. A problem with existing federated networks is that users lose their identities tied to their accounts on a specific server if that server shuts down. 

To enable easy ways to switch servers, maintain social graphs between different providers, and protect users from sudden shutdowns, AT protocol incorporates data repositories and decentralized identifiers (DIDs). 

Data repositories are signed data collections that function akin to GitHub repositories, but they’re for database records that include users’ public activities. 

DIDs allow using digital identities across many platforms and blockchains while protecting users’ privacy and ensuring security. As with most protocols, Bluesky will also use the W3C standard for deploying DIDs.

Handling user data with data repositories and integrating DIDs increases account portability across servers. 

Interoperability and scalability

AT protocol uses a schema-based interoperation framework called Lexicon to enable better coordination across different servers. The framework helps unify names and basic social behaviors. 

To improve scalability, the protocol distinguishes between small-world and big-world networking. While the former includes specific uses like mentions, replies, and DMs, the latter refers to large-scale metrics like followers, shares, likes, and content discovery. 

Trust and algorithmic choice

Algorithms decide what we see in our social media feeds. The AT protocol includes an open algorithms mode, giving users more choices to control the algorithm. Users will have different ways to audit the performance of the services, and they will be able to leave the service if unsatisfied. 

AT protocol uses self-authenticating data and verifiable computations to establish trust and protect privacy. They will help retain metadata and build reputation graphs. 

A hybrid federated network with peer-to-peer characteristics 

While all of these remind us of blockchain, the company noted explicitly that the team is not focused on building a specific blockchain network; instead, they’re exploring novel applications for distributed social networks. 

The team members previously developed decentralized web protocols and blockchain networks. The AT protocol aims to synthesize the earlier experience and knowledge into a new protocol that leverages self-authenticating data and identities by adding p2p characteristics to the mix. As the CEO of Bluesky, Jay Graber, tweeted, one such characteristic is the content-addressing module of IPFS.