Shielded Bitcoin would use zero-knowledge proofs and encrypted notes to hide transaction details without changing Bitcoin consensus, but researchers have raised questions about anonymity and quantum resistance.

Researchers at the cryptography research firm Alloc Init have proposed a system for bringing Zcash-style private transfers to Bitcoin without requiring a soft fork.

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

The proposal offers a potential path to stronger privacy for Bitcoin users without requiring consensus changes to the base protocol.

Instead of having miners enforce the privacy protocol, Shielded Bitcoin would use Bitcoin as “a neutral publication and ordering layer,” the researchers wrote. Separate software called indexers would then verify zero-knowledge proofs, check that funds haven’t been double-spent, and reconstruct the state of the shielded system.

Shielded Bitcoin’s design explicitly draws from Zcash’s architecture. The researchers said it similarly uses encrypted notes, public nullifiers that mark notes as spent, and zero-knowledge proofs that show transactions are valid. Unlike Zcash, Shielded Bitcoin would not operate its own blockchain or consensus mechanism.

Developer Vadim Zavodil criticized the proposal on X, arguing that much of its privacy stack had already been implemented by Zcash. He questioned how much privacy a newly launched system could initially provide, arguing that a new shielded pool would start without the anonymity set Zcash has accumulated over years of use.

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