The Fedimint team pulled off a cross-implementation test at Ecash Hackday in Berlin, running a single federation across three independent implementations. One of those implementations was built by Cashu developer thesimplekid. The demonstration matters because fedimint's architecture only delivers its security guarantees if no single piece of software becomes a single point of failure.
Federated Cashu and the Blind BLS signature scheme
Calle unveiled a design called Federated Cashu at bitcoin++. The scheme lets any four or five operators keep a federation running, using a new Blind BLS signature scheme. In practice, that means the federation can tolerate some operators going offline without the whole system grinding to a halt.
The timing is notable. Bitcoin++ has become a regular venue for fedimint and Cashu developers to compare notes on custody models that sit somewhere between a single custodian and a full on-chain multisig setup.
Matt Corallo's software monoculture warning
Matt Corallo critiqued software monoculture, pointing out that running the same software means suffering the same bugs. It's a familiar argument in Bitcoin infrastructure circles, but it lands differently when the thing being run is a federation holding user funds. A bug in one implementation, replicated across every operator, is a bug in every federation.
Obi Nwosu, co-founder of Fedi and fedimint, laid out five layers where independence has to hold. Multiple implementations of every protocol that holds funds. Multiple wallet implementations. Keys generated on hardware from different vendors. Multiple independent trustworthy people behind every system that holds money. And distribution across geographies and jurisdictions.
That's a tall order. It's also the difference between a federation that fails gracefully and one that fails everywhere at once.
Who builds the fourth implementation?
The fedimint developers' response to Corallo's monoculture point was blunt: they asked who will build the fourth implementation. Three implementations exist now. A fourth would widen the gap between any single bug and the federations it could take down. Nobody has publicly volunteered yet.
Fedimint is the open-source protocol. Fedi is the company built on top of it. Keeping those two things distinct matters when reading announcements, because protocol-level work and product-level work move at different speeds and answer to different incentives.
An open question, not a finished story
The Berlin demo and the Federated Cashu design are milestones, but they don't close the loop. The five-layer independence standard Nwosu described still depends on someone building that fourth implementation, and on operators actually sourcing hardware from different vendors instead of whatever is cheapest and available.
For now, the concrete next step is watching whether a fourth fedimint implementation gets announced and who steps up to build it.
The article was originally published in Bitcoin Magazine as a guest post by Obi Nwosu. Opinions expressed are his own and do not necessarily reflect those of BTC Inc. or Bitcoin Magazine.
