Bitcoin Could Get Zcash-Style Privacy — Without Changing Bitcoin Itself

Bitcoin has never been private — its ledger is public by design. Now researchers at the cryptography firm Alloc Init say they can fix that without touching Bitcoin's consensus rules at all.

The proposal, called Shielded Bitcoin, would conceal transaction amounts, senders, receivers, and links to previously spent funds using encrypted notes and zero-knowledge proofs, according to Cointelegraph. The paper was published by Clara Shikhelman, Mikhail Komarov, and Aleksei Moskvin.

How it works

Rather than asking miners to enforce a privacy protocol — which would require a consensus change — Shielded Bitcoin treats Bitcoin as what the researchers call "a neutral publication and ordering layer." Separate software, dubbed indexers, would verify the zero-knowledge proofs, check that funds haven't been double-spent, and reconstruct the state of the shielded system.

The architecture draws explicitly from Zcash: encrypted notes, public nullifiers that mark notes as spent, and zero-knowledge proofs showing transactions are valid. Unlike Zcash, the system would run no blockchain or consensus mechanism of its own.

The skeptics push back

The proposal drew mixed reactions. Developer Vadim Zavodil argued that much of the privacy stack was already implemented by Zcash and questioned how much privacy a brand-new system could offer on day one: "Privacy is a function of the crowd. Zcash has a real shielded pool built over years," he wrote. "A brand new metaprotocol starts at zero, so your first private transfer hides in a crowd of one."

The researchers themselves acknowledged a version of that limitation in a companion post, noting that large deposits don't automatically create a large anonymity set — observers could still narrow down relationships between transfers if a small number of actors create most notes.

A second critique came from Pierre-Luc Dallaire-Demers, founder of post-quantum cryptography firm Pauli Group, who called the construction interesting but "not quantum resistant at all." He said he was exploring what a fully post-quantum version could look like, assuming Bitcoin eventually adopts a post-quantum signature scheme.

A supportive nod from the originals

One voice was more encouraging: Zerocash co-author and StarkWare CEO Eli Ben-Sasson said the original intent behind the Zerocash paper — which preceded Zcash — was to bring privacy to Bitcoin. He said he hadn't yet read the paper but would like to see the vision of privacy and scalability through zero-knowledge proofs materialize on Bitcoin's base layer.

If Shielded Bitcoin gets built and the crowd shows up, Bitcoin users could one day transact privately without waiting for the network to agree to change. The crowd, as ever, is the hard part.

Written by the BidAsk Newsroom. Based on reporting from the sources below.