Researchers at Bitcoin cryptography firm Alloc Init have proposed Shielded Bitcoin, a design for Zcash-style private transfers on Bitcoin that requires no soft fork or consensus change. The 56-page paper, dated September 24 and authored by Clara Shikhelman, Mikhail Komarov and Aleksei Moskvin, would conceal a payment’s sender, recipient and amount while publishing the transaction data directly on Bitcoin’s base layer. Value would be represented as encrypted notes, with each transfer using a zero-knowledge proof to show ownership and prove that no value was created or destroyed. A public nullifier would prevent double spending without revealing the note being spent. Unlike Zcash, which tracks shielded balances on its own blockchain, Shielded Bitcoin would rely on deterministic indexers to replay Bitcoin’s accepted transaction history and reconstruct identical private records. The proposal says wallet keys retain spending authority and that indexers cannot move users’ funds. The current paper addresses transfers within the system, while deposits and withdrawals are reserved for a separate protocol based on Bitcoin PIPEs v2. Each transfer would publish a proof through OP_RETURN, adding a fee to standard Bitcoin network costs; the paper cites proof sizes of roughly 160 to 192 bytes depending on the proof system. Existing design details describe Groth16, an OP_RETURN footprint of about 625 vbytes for two inputs and two outputs, and an estimated private transfer size of about 700 vbytes, or roughly four times standard Bitcoin miner fees. Open questions include wallet verification without replaying the entire Bitcoin blockchain and the standard number of inputs and outputs. An optional compliance feature would let institutions verify that funds came from approved sources and passed through certified recipients without exposing the underlying history. The proposal is part of a wider effort to bring privacy features to Bitcoin and arrives during renewed interest in privacy coins.