Alpen Labs was one of the many highly shitcoin-adjacent attempts at building something on Bitcoin. I haven't heard much about them in the last few months, but it looks like they are still working on things. I'm not terribly optimistic that any of these things bear fruit, but that doesn't mean people shouldn't work on them.

We present Mosaic, a protocol that achieves malicious security via cut-and-choose but reduces the on-chain footprint so that it is independent of the number of garbled copies. The key technique, first introduced by Eagen (Glock, 2025) in this setting, is polynomial label correlation: labels across all garbled copies are arranged as evaluations of a degree- polynomial, so the shares revealed during cut-and-choose fall one short of the reconstruction threshold. We use adaptor signatures to arrange that the prover's on-chain witness commitment reveals the missing share as a byproduct; the evaluator then reconstructs labels for all unchallenged copies by interpolation. We sketch why Mosaic is secure against a malicious prover and verifier and instantiate it for trust-minimized Bitcoin bridging with a Groth16 verifier circuit, a full protocol specification, and a Rust implementation.

There is a repository as well:

Mosaic is the garbled-circuit component of Strata Bridge, a Bitcoin ↔ Alpen L2 bridge. Each bridge operator runs a Mosaic node; Mosaic peers exchange garbling material over QUIC and execute the Mosaic protocol's Garbler and Evaluator state machines.

This repository contains a full-stack open-source implementation: the mosaic node binary, the protocol crates, storage and network handling, Docker configuration, and a functional-test harness.