Researchers Propose Zcash-Style Privacy for Bitcoin Without a Soft Fork

Cryptography research firm Alloc Init has unveiled a proposal called Shielded Bitcoin that would bring Zcash-style private transfers to the Bitcoin network without requiring a consensus-altering soft fork. The paper, published Thursday by researchers Clara Shikhelman, Mikhail Komarov, and Aleksei Moskvin, outlines a system that conceals transaction amounts, senders, receivers, and links to previously spent funds using encrypted notes and zero-knowledge proofs.

Rather than modifying Bitcoin's base protocol, Shielded Bitcoin leverages the existing blockchain as "a neutral publication and ordering layer," according to the researchers. Separate software known as indexers would handle the heavy lifting, verifying zero-knowledge proofs, preventing double-spending, and reconstructing the state of the shielded system. The design closely mirrors Zcash's architecture, employing encrypted notes, public nullifiers that mark notes as spent, and cryptographic proofs confirming transaction validity—without requiring an independent blockchain or consensus mechanism.

The proposal has drawn measured responses from the crypto community. Developer Vadim Zavodil criticized the plan on X, arguing that much of its privacy stack replicates existing Zcash functionality. He questioned the practical anonymity a new shielded pool could offer, noting that "privacy is a function of the crowd. Zcash has a real shielded pool built over years. A brand new metaprotocol starts at zero, so your first private transfer hides in a crowd of one." The Alloc Init researchers acknowledged this limitation in a companion post, conceding that large deposits do not automatically generate a robust anonymity set and that observers could potentially narrow down relationships between transfers.

Pauli Group founder Pierre-Luc Dallaire-Demers raised additional concerns about quantum resistance, describing the construction as interesting but flagging unresolved issues around long-term cryptographic security. The discussion comes as Zcash itself prepares for a November upgrade that could potentially freeze funds in its legacy Sprout pool, adding urgency to the broader debate over how best to deliver on-chain financial privacy on Bitcoin.