Researchers from Alloc Init, a cryptography research firm, have introduced a new proposal aimed at enabling private transfers on the Bitcoin network with features similar to Zcash, all without requiring a soft fork to the existing protocol.
Shielded Bitcoin: Bringing Privacy to Bitcoin Transactions
The proposal, named Shielded Bitcoin, intends to obscure transaction details such as amounts, sender and receiver addresses, and links to previously spent outputs. This would be achieved through the use of encrypted notes, public nullifiers marking spent notes, and zero-knowledge proofs to verify transactions without exposing sensitive information.
Zcash is a blockchain known for enabling confidential transactions using advanced cryptographic techniques. Its privacy features have set a standard in the crypto sector for concealed transfers. The Shielded Bitcoin system draws directly from these privacy methods but is tailored for Bitcoin users.
Clara Shikhelman, Mikhail Komarov, and Aleksei Moskvin authored the research paper behind the project. Unlike Zcash, Shielded Bitcoin does not plan to operate a separate blockchain or its own consensus protocol, instead focusing on providing privacy enhancement as an optional service for Bitcoin.
Mini dictionary: Alloc Init is a cryptography research company that designs privacy protocols for blockchain networks.
Limitations and Privacy Considerations
The team behind Shielded Bitcoin acknowledged inherent limitations of their approach, particularly in relation to the privacy set available for users. In a detailed post, the researchers noted that creating larger deposits may not automatically expand the anonymity set. If privacy transactions are limited to a few active users or have distinctive wallet behaviors, it may still be possible for observers to deduce relationships between transfers.
They highlighted that increasing deposit size alone will not enlarge the anonymity set, cautioning that “observers may still be able to narrow down relationships if a small number of actors create most notes or wallets exhibit distinctive behavior.”
Community Response and Quantum Resistance Concerns
Pierre-Luc Dallaire-Demers, founder of Pauli Group, a company specializing in post-quantum cryptography, reviewed the research and raised concerns regarding quantum resistance. He found the Shielded Bitcoin construction technologically interesting but said it currently lacks protection against quantum attacks. He added that he is exploring ways a fully post-quantum version could be developed if Bitcoin upgrades to post-quantum signature schemes in the future.
Mini dictionary: Pauli Group is a research organization focused on developing cryptographic algorithms that can withstand quantum computer attacks.
Dallaire-Demers considered the system “interesting but not quantum resistant at all” and intends to investigate possible solutions using post-quantum signatures for Bitcoin.
