Researchers have published a proposal for "Shielded Bitcoin," a system modeled on Zcash's privacy protocol that would conceal payment amounts, senders and recipients without requiring any changes to Bitcoin's underlying network rules.
The 56-page specification, released Thursday by Clara Shikhelman, Mikhail Komarov and Aleksei Moskvin of the cryptography firm [alloc] init, would store encrypted transfers on Bitcoin while leaving verification to separate software anyone can run. Under the design, bitcoin-denominated value would be held in encrypted records called notes. Spending one note publishes a marker showing it has been used, along with a zero-knowledge proof that the sender owned the funds and created no new ones, while keeping the amount, sender and recipient hidden.
Because Bitcoin nodes currently check every transaction against a single shared rulebook, a confirmed block proves the network accepted the payment. Shielded Bitcoin diverges from that model: it would publish private-transfer data on-chain but delegate validation to independent software. A Bitcoin transaction could therefore be confirmed even if the shielded payment recorded inside it failed the system's own checks.
The proposal comes as privacy concerns have surfaced among developers building cryptocurrencies for payroll, business payments and everyday transactions. Standard Bitcoin transactions permanently expose amounts and addresses, and once an address is linked to an entity, follow-on payments become easier to trace. Shielded Bitcoin would retain encrypted transfer data on-chain so users with wallet keys could reconstruct accepted payments from the public record, while separate viewing keys would allow disclosure to accountants or auditors without granting spending permission.
Zcash has seen renewed activity alongside the research. Its shielded pools held approximately 4.9 million ZEC on Friday, up 14% from July 30 and representing roughly 29% of issued coins worth about $7.8 billion, according to CoinDesk calculations using ZecStats data. Zcash recorded roughly 63,000 shielded transactions last week — its busiest week for private transfers since 2022 and fourth-highest on record — with reported transfer volume exceeding $23 billion, the largest weekly total since 2021.
ZEC gained more than 2,300% over the preceding year and crossed $1,000 by early September, extending above $1,600 Wednesday. The coin's origins trace back to the 2013 Zerocoin proposal, a privacy extension to Bitcoin, with subsequent Zerocash research spawning Zcash's launch as a standalone network in 2016.
The paper does not explain how ordinary BTC would enter the system or be redeemed on withdrawal. The authors reserved those mechanisms for a separate publication using PIPEs, a technique designed to lock a Bitcoin signing key until specified conditions are met, noting their claim that users retain control covers internal transfers and "explicitly excludes deposits and withdrawals."
Mert Mumtaz, cofounder of Solana infrastructure provider Helius and a Zcash supporter, called the proposal on X "a synthetic ledger with significant tradeoffs." He pointed to the need for a trusted setup, absent fee anonymization — meaning the Bitcoin wallet paying to publish a private transfer remains visible — and the lack of an in-protocol deposit or withdrawal mechanism. "You are holding synthetics," he wrote, adding the proposal would require years of additional research and development.
Cypherpunk, a company that holds and mines Zcash, said the research was welcome but did not see it as competition. "Privacy works best when built into the base layer. Not requiring Bitcoin changing is this design's biggest selling point, and also its biggest drawback," the company wrote.
[alloc] init acknowledged several limitations: the reference design requires a cryptographic setup whose security depends on at least one participant acting honestly, transfer timing and fee payments remain visible, and an efficient method for lightweight wallets to verify reconstructed payment history was listed as future work.
