Researchers Propose Zcash-Style Private Bitcoin Transfers Without a Soft Fork

How Shielded Bitcoin Works

Shielded Bitcoin aims to bring Zcash-like privacy features to the Bitcoin network without protocol changes. The system uses encrypted notes, public nullifiers to mark spent notes, and zero-knowledge proofs to validate transactions privately.

Instead of miners enforcing privacy rules, Bitcoin serves as a “neutral publication and ordering layer.” Separate software called indexers verify zero-knowledge proofs, prevent double-spends, and reconstruct the shielded system’s state.

Architecture Inspired by Zcash with Key Differences

Shielded Bitcoin’s design draws heavily from Zcash’s privacy architecture, incorporating encrypted notes, nullifiers, and zero-knowledge proofs to hide transaction details and prove validity.

Unlike Zcash, which operates on its own blockchain with a distinct consensus mechanism, Shielded Bitcoin retains Bitcoin’s original blockchain and protocol untouched, foregoing the need for its own chain or consensus.

Community Reactions and Critiques

Developer Vadim Zavodil criticized the proposal on the social platform X, stating many privacy components have already been implemented by Zcash, and questioned the privacy effectiveness of a newly launched system with no established anonymity set. He emphasized that privacy depends on crowd size, noting a brand new metaprotocol essentially starts with an anonymity set of one.

The Shielded Bitcoin authors acknowledged this limitation, admitting that large deposits don’t automatically create large anonymity, and that observers can potentially trace relationships if few actors dominate note creation or wallets behave distinctly.

Pierre-Luc Dallaire-Demers, founder of post-quantum cryptography firm Pauli Group, pointed out that the current design lacks post-quantum resistance. He is exploring what a fully post-quantum version might entail, anticipating Bitcoin’s possible adoption of post-quantum signature schemes.

Eli Ben-Sasson, CEO of StarkWare and co-author of Zerocash, expressed support for the overall direction, recalling that the original Zerocash paper intended to bring privacy to Bitcoin. He stated interest in seeing the combination of privacy and scalability via zero-knowledge proofs realized on Bitcoin’s base layer.