Bull Bitcoin Introduces Payjoin for Privacy-First Deposits, Withdrawals, and Trading

Bull Bitcoin has unveiled a comprehensive Payjoin integration for its exchange, asserting it is the first global Bitcoin exchange to provide Payjoin for both deposits and withdrawals. The upgrade introduces two novel features: “Payjoin-by-default and Payjoin trading,” the press release shared with Bitcoin Magazine states.

Established in Canada in 2013 by Francis Pouliot, Bull Bitcoin holds the title of the world’s longest-running Bitcoin-only exchange. Its non-custodial platform enables users in Canada, Europe, and Latin America to purchase Bitcoin directly into their own wallet and to sell Bitcoin to their bank accounts. Additionally, Bull Bitcoin develops BULL Wallet, a free and open-source self-custodial Bitcoin wallet. The company has remained self-funded since its founding.

Payjoin is a Bitcoin on-chain privacy protocol that challenges fundamental assumptions of on-chain analysis firms regarding user behavior. One such assumption is that one of the unspent transaction outputs (UTXOs) from a Bitcoin transaction will be change returned to the sender. Another assumption is that amounts are often denominated in dollars. Payjoin protocols introduce an off-chain coordination layer so that amounts sent and returned to the sender obscure user intent, thereby protecting their privacy on-chain. Payjoin does not require a hard or soft fork of Bitcoin consensus. Rather, it requires adoption by user wallets and exchanges to scale, yet it does not depend on collective action to benefit individual users. Bull Bitcoin’s Payjoin integration is closely based on the Payjoin Foundation’s work.

Whenever a BULL Wallet user buys or sells Bitcoin on-chain through the built-in exchange, that transaction will automatically be a Payjoin. This enables Bitcoin buyers to passively consolidate their wallet’s UTXOs, which can lower their future Bitcoin mining fees. “Many Bitcoin users do not even know that they must periodically “merge” their coins by spending them to a new address in their Bitcoin wallet, if they want to reduce the economic costs of future Bitcoin transactions,” the press release explained. Payjoin-by-default automates this process. This not only helps shrink Bitcoin’s UTXO set, making node operation easier for everyone, but also reduces fee pressure for all Bitcoin users.

Payjoin trading is a new concept that safeguards users against malicious entities attempting to glean insights into their financial behaviors through chain analysis. Since Bitcoin transaction amounts are public, it is possible to reverse-engineer information such as someone’s salary or trading strategies like dollar-cost averaging. Bull Bitcoin is a non-custodial exchange, so every trade leaves an on-chain trail.

Widespread adoption of Payjoin in the Bitcoin network renders common input ownership and change output detection heuristics less dependable. Bull Bitcoin’s Payjoin implementation reduces round-number amounts in sent transactions and address reuse, and lowers the likelihood of third-party observers guessing the fiat value of Bitcoin transactions. The introduction of Payjoin-by-default and Payjoin trading means that the more users Bull Bitcoin has, the more privacy the Bitcoin network achieves overall; “This is part of our philosophy to align the incentives of our company with the interests of all Bitcoin users.”

In December 2024, BULL Wallet became the first Bitcoin wallet globally to integrate the Payjoin V2 protocol. This was a highly experimental initiative coordinated with Dan Gould and the Payjoin Dev Kit team, who have since founded the Payjoin Foundation.

Researchers have utilized insights from this experimentation to enhance the Payjoin experience, making it more seamless and attack-resistant. The software behind Payjoin, for both wallet and exchange, is completely free and open-source.