Key Transparency (in support of end-to-end encryption) on the Fediverse.

What is this?

Any attempt to build End-to-End Encryption for the Fediverse will confront a difficult engineering challenge: How do your users know which Public Key belongs to someone they want to communicate with?

Historically, there have been many attempts to solve this problem:

• SSH, by default, asks the user to manually verify a key fingerprint and then trusts only that key fingerprint unless manually changed by the user.
• TLS, which protects most web traffic, requires Certificate Authorities that are trusted by your browser or Operating System.
• PGP encouraged a "Web of Trust" system that was complicated and brittle.

Any system that attempts to solve this problem at scale is called a Public Key Infrastructure.

Neither of the above approaches are a good fit for the Fediverse. However, there is a reasonable precedent: To keep the Certificate Authorities honest, cryptographers and engineers invented Certificate Transparency, built on an append-only data structure called a Merkle Tree.

The Public Key Directory adopts ideas from Certificate Transparency in order to have a Federated Public Key Infrastructure without Authorities.

Key Features

📜 Append-Only Transparency Log

All key events are recorded in an append-only ledger built with a Merkle Tree, ensuring an honest view of history.

🔍 Verifiable Auditing

Anyone can verify the consistency and integrity of the key directory.

✂️ Shreddable History

GDPR takedown requests are possible through granular key erasure.

🌐 Distributed Trust

Witness co-signing and verifiable replication.

➕ Auxiliary Data (Advanced)

Developers can build atop the PKD to add key transparency to other systems.

❌ In-Band Revocation

Attackers cannot selectively censor revocation; it’s all-or-nothing.

Learn More

• Read the Specification
• Key Transparency — activitypub-e2ee issue tracker
• Fediverse Auxiliary Service Provider Discussion

Project Status

• Specification: v0.3.0
• Server-side reference implementation: v0.3.0
• Client-side reference library: v0.2.0