Researchers propose Zcash-style private Bitcoin transfers without a soft fork

Researchers at Alloc Init have proposed a system called Shielded Bitcoin to provide Zcash-like privacy for Bitcoin transactions without requiring a soft fork of Bitcoin’s consensus rules. The design hides transaction amounts, senders, receivers and links to previously spent funds by using encrypted notes and zero-knowledge proofs, while relying on Bitcoin only as a neutral ordering and publication layer.

Rather than making miners or the base protocol enforce privacy rules, Shielded Bitcoin would depend on separate indexer software to verify zero-knowledge proofs, check that notes have not been double-spent via public nullifiers, and rebuild the state of the shielded system off-chain. The researchers say the construction draws explicitly from Zcash’s architecture — including encrypted notes and nullifiers — but it would not run its own blockchain or consensus mechanism.

The proposal drew mixed responses from the crypto community. Developer Vadim Zavodil argued on X that a newly launched shielded layer would lack the large anonymity set that Zcash has accumulated over years, and that privacy effectiveness depends heavily on the size and behavior of the crowd using the system. The Alloc Init authors acknowledged that a small number of actors or distinctive wallet behavior could allow observers to narrow relationships between transfers even with shielded notes.

Others raised different technical concerns. Pierre-Luc Dallaire-Demers, founder of Pauli Group, called the construction "not quantum resistant at all," and said he was investigating how a fully post-quantum variant might be realized if Bitcoin moved to post-quantum signatures. By contrast, Eli Ben-Sasson, co-author of the Zerocash paper and CEO of StarkWare, expressed support for pursuing privacy and scalability through zero-knowledge technology on Bitcoin, noting that bringing those ideas to Bitcoin had been an original aim of earlier work.

The paper presents a potential path to stronger privacy without changing Bitcoin’s base protocol, but authors and commentators highlight practical hurdles — including bootstrapping anonymity sets and addressing post-quantum risks — that would influence how effective and resilient such a system could be in practice.