The Trailing Finality Layer

We’ve just published v0.1.0 of the TFL Book.

This version of the design includes the Crosslink construction, a hybrid consensus protocol which integrates PoW and PoS subprotocols. The Crosslink doc has security proofs of safety and liveness properties. This represents the first milestone with a specific abstract hybrid PoW/PoS protocol defined.

This v0.1.0 version has the content split between the TFL Book and a separate hackmd defining the Crosslink construction. The next milestone will integrate the Crosslink definition into the book ensuring it’s self-consistent.

The short-to-medium term roadmap for Trailing Finality Layer is to bolster this initial version of Crosslink with simulations of various attacks and more in-depth analysis of attacks, as well as beginning to examine real-world PoS protocols to integrate into the hybrid construction.

The medium term roadmap (within the next ~3 or so months), we’re considering a variety of steps beyond the roadmap defined above:

  • Complete TFL protocol:
    • Define a specific PoS subprotocol integration.
    • Define staking operations which are integrated with Zcash transaction semantics.
    • Define staking parameters and analyze their security and economic properties.
  • Begin creating a prototype / testnet.
  • Crosslink:
    • Get broader review of Crosslink security.
    • Compare Crosslink to other known viable hybrid protocols.
  • Begin designing a transition plan for transitioning Zcash from PoW to PoW+TFL.

In addition to the direct work on Trailing Finality Layer, we’re aware of multiple projects or people interested in bridging protocols or systems, so we hope to engage with them and ensure the design of Trailing Finality Layer can integrate and/or support trust-minimized bridge protocols.

As always, feedback is appreciated!

Shout out to Daira Emma Hopwood who has done most of the research and design behind Crosslink. <3