Feedback from implementations fuels our growth, and we want to thank Cake Wallet for being their close collaboration and reporting which helped lead to our stable rust-payjoin 1.0 release candidate. Just now, they have offered generous material support to the Payjoin Foundation to continue operations.

Cake wallet has been leading the way on the cutting edge of Bitcoin privacy technology and user experience. Async Payjoin is now their default Bitcoin flow, and their early support helps us improve so that more wallets and software may interoperate with Cake's use of the BIP 77 standard.

Cake wallet also runs an OHTTP Relay which users can use to reach Payjoin Directories, making the Payjoin infrastructure more robust and decentralized.

Vik's incessant Payjoin evangelism has brought Payjoin to a new audience at conferences, online, and in my experience even on the fly at chance meetings in restaurants. His message is clear: the world needs more Payjoin, and the time to support it is now. Seth has been a pleasure to work with since the beginning of the project, nudging developers to use the tools, offering his hand to contribute edits to the upstream source to improve the developer experience, and of course convincing the Cake team Payjoin needs doing. Konstantin has been the most reliable implementing developer, getting up at odd hours to service requests from our team and user feedback, and contributing his feedback to inform the integration upstream. The Cake pilot integration brings Async Payjoin to hundreds of thousands of devices.

Their recent generous donation to Payjoin Foundation additionally bolsters our ability to recruit and improve the core protocol libraries.

Thank you Cake for your generous support. The future of Bitcoin depends on it.

Spiral Bitcoin Wizard and longtime Bitcoin privacy developer Yuval Kogman joins Payjoin Foundation as the first Advisory Board member. He draws on more than two decades of programming experience. Few others can boast Yuval's dedication to the Bitcoin privacy niche. He is perhaps best known for his work developing the WabiSabi DoS prevention protocol. His subsequent whistleblowing of privacy vulnerabilities in CoinJoin implementations, including those touting WabiSabi integration, demonstrates his commitment to the underlying principles.

Commercial attempts to solve Bitcoin’s privacy problems have faced tremendous barriers. Short-term profit motives have delivered partial and temporary solutions, but transacting privately on Bitcoin remains a challenge.

We formed Payjoin Foundation to pursue the long-term mission of addressing Bitcoin’s privacy problems. Our non-profit exists to develop open-source protocols that align economic incentives with network-wide privacy protection. We believe that users have a right to choose whether or not to reveal their on-chain activity, and that such protocols can even offer a more convenient and delightful experience than those that don't respect this choice.

Liana secures bitcoin such that after time passes, if and only if you haven't yet spent your coins, your heirs can spend them. This condition is called a "timelock" contract. To prevent unintentional activation of this inheritance policy, these timelocked coins require periodic refreshing by being spent into a new timelock. Liana's Payjoin integration automates timelock refresh as payments are received, boosting privacy and cutting costs.

Due to a docker misconfiguration, the payjo.in directory server had an open redis database, allowing unauthorized parties to observe exchanges between pairs of senders which only support BIP 78 and receivers which support BIP 77.

Some payjoins which used the backwards compatibility of BIP 77 receivers with BIP 78 senders during this period may thus not have the common input ownership heuristic protection they otherwise would, but the unauthorized access does not change the nature of the risk regarding the user custody of funds.

The following is a conclusive address of concerns around UTXO probing attacks on Payjoin, clarification of why current mitigations are effective, and definitive argument for Payjoin adoption. Payjoin, the fundamental interactive transaction batching protocol, saves fees by reducing the effective size of transfers and improves privacy by disrupting common blockchain surveillance heuristics. While probing attacks exist in theory, they're costly to pull off, mitigated in practice, and are not a meaningful barrier to adoption.

Payjoin is a transformative protocol that enables wallets to communicate and create collaborative, smarter, and more efficient Bitcoin transactions. It offers payment batching technology that exchanges and payment processors can use to save on fees and protect their own and their users' financial privacy while scaling Bitcoin.

Payjoin V1 coordinates transactions between two parties who communicate over a public server endpoint secured by either TLS or Tor hidden service hosted by the receiver. This requires setting up either an HTTPS proxy or a Tor proxy when testing payjoins across different implementations.

On July 27, HRF announced a 2 BTC bounty for a production deployment and specification of a version 2 payjoin spec to receive payjoin without hosting a server. This past week I proposed a new BIP and call for feedback in search of consensus on what that spec should be. Many new ideas were born. This is my attempt to make sense of them.

PDK is here to make Payjoin a drop in upgrade for all software touching Bitcoin. I cover the project's history, why you should consider it to add Payjoin to your stack, and some of the project's priorities moving forward. The PDK team will be updating this new blog with development updates, feature forecasts and the details of releases.