Researchers at Alloc Init have proposed Shielded Bitcoin, a metaprotocol designed to conceal transaction amounts and counterparties on the Bitcoin network without modifying Bitcoin's consensus rules or relying on trusted intermediaries.
The proposal, presented by Clara Shikhelman, Mikhail Komarov, and Aleksei Moskvin, adapts the encrypted-note approach used by Zcash but implements it directly on Bitcoin's base layer using cryptographic proofs.
How the Privacy Layer Works
Bitcoin's public ledger currently exposes transaction amounts, timing, and links between addresses. Shielded Bitcoin would move value into encrypted notes, each containing an amount and recipient information. When a transaction occurs, a wallet publishes encrypted notes to Bitcoin alongside a zero-knowledge proof that confirms the notes exist, the sender is authorized to spend them, and amounts balance—all without revealing specific details.
Software called indexers would verify these proofs and track nullifiers, unique serial numbers that prevent notes from being spent twice. Because anyone can run indexers, no single party controls the ledger.
The design separates spending and viewing rights through multiple keys. One key authorizes spending, another detects incoming transfers in read-only mode, and a third recovers transaction history. This separation allows users to share limited transaction details with others without exposing spending authority.
Comparison to Existing Privacy Solutions
Several privacy approaches already exist for Bitcoin. Methods like CoinJoin, PayJoin, and Silent Payments operate within Bitcoin's current transaction format and can obscure ownership but leave amounts and transaction patterns visible.
Zcash represents the closest precedent, using encrypted notes, nullifiers, and zero-knowledge proofs. However, Zcash operates on its own blockchain and consensus rules, while Shielded Bitcoin derives its state from Bitcoin's history. This distinction means transaction patterns and repeated fees could still allow observers to narrow down relationships over time.
Grayscale research has noted that artificial intelligence tools are making it easier to link wallet addresses to real identities, suggesting privacy solutions may become increasingly important for privacy-conscious users.
