A new paper released on Thursday outlines a method for conducting private Bitcoin transactions without altering Bitcoin’s core protocol. The proposal, called Shielded Bitcoin, adapts the encrypted payment mechanism used by Zcash to conceal transaction amounts, senders and recipients.

The system would store encrypted transfers on Bitcoin while relying on separate software to validate them. Under this design, a Bitcoin transaction could be confirmed even if the private payment failed its own verification checks. The researchers emphasized that the approach does not require changes to Bitcoin’s network rules.

Privacy has become a growing focus for cryptocurrency developers as digital assets expand into use cases like payroll, business payments and donations. Ordinary Bitcoin transactions expose amounts and addresses permanently, making it easier to trace activity when an address becomes linked to an individual or organization. Shielded Bitcoin aims to address this limitation while preserving the security of the Bitcoin network.

The concept draws on Zcash’s shielded pool architecture, where funds are held in encrypted records called notes. Spending a note would publish a marker indicating its use, along with a mathematical proof that the sender owned the funds and did not create new ones. The amount, sender and recipient would remain hidden from public view.

Zcash validates these proofs directly on its blockchain. In contrast, Shielded Bitcoin would publish transfer data on Bitcoin and delegate verification to external software that anyone could run. This distinction means Bitcoin would store the data but perform no validation of the private payments.

Zcash’s shielded transactions have seen increased activity recently. On Friday, shielded pools held approximately 4.9 million ZEC, representing about 29% of all issued coins and valued at roughly $7.8 billion. The network processed around 63,000 shielded transactions in a single week, its busiest period for private transfers since 2022. Across the Zcash network, transfer volume exceeded $23 billion in the same week, marking the second-highest total in its history.

The price of ZEC has risen sharply over the past year, gaining more than 2,300% and briefly surpassing $1,600 in early September. This surge reflects growing interest in privacy-preserving cryptocurrencies.

Shielded Bitcoin would allow users to reconstruct accepted payments using their wallet keys and viewing keys, enabling them to prove transaction history to auditors without granting spending authority. However, the paper does not address how Bitcoin would be deposited into or withdrawn from the system. The authors note that mechanisms for handling actual BTC transfers would be detailed in a separate document using PIPEs, a technique for locking signing keys until specific conditions are met.

Critics have raised concerns about the proposal’s limitations. Mert Mumtaz, a developer associated with Helius and a Zcash advocate, described the concept as “a synthetic ledger with significant tradeoffs” on social media. He highlighted the reliance on a trusted cryptographic setup and the absence of fee anonymization, noting that the originating Bitcoin wallet would remain visible during transaction publishing.

The research team acknowledges several open questions. The 56-page specification does not clarify deposit and withdrawal processes, and the referenced PIPE mechanism remains undeveloped. Additionally, private transfers would require approximately 700 virtual bytes of data compared to 100–200 bytes for standard Bitcoin transactions, potentially leading to higher transaction fees at equivalent rate levels.

No timeline for implementation has been provided. The proposal remains in the conceptual stage, with further research needed to address technical and operational challenges.