Chat_173 - The Time Has Come for Privacy on Bitcoin with Dan Gould

— Payjoin fundamentals: Payjoin is an interactive protocol where sender and receiver communicate to create a single transaction with inputs from both parties, breaking Satoshi's assumption that all inputs come from one person.

— Privacy at the base layer: Dan argues Bitcoin privacy must be automatic and built into base-layer settlement, not opt-in wallet features, to achieve meaningful anonymity sets and resist surveillance.

— Async Payjoin and mailboxes: The new V3 protocol uses HTTP Oblivious HTTP with dumb public mailboxes (like Nostr relays) so sender and receiver can communicate encrypted messages without revealing IP addresses or trusting a central server.

— Why earlier privacy tools failed: TumbleBit was too early (pre-FinCEN guidance) and too complex; Wasabi coinjoins succeeded because they were simple and could monetize coordination; original Payjoin adoption stalled because it required merchants to run servers.

— Developer Kit and wallet integration: The Payjoin Dev Kit (now in Rust, Dart, Python, C#) lets wallets integrate with ~2,000 lines of code. Bull Bitcoin mobile, Cake Wallet, and others now pilot V3; more integrations expected in 2025.

— Settlement vs. payments distinction: Payjoin targets on-chain settlement between entities (exchanges, nodes, Arc providers), not everyday coffee payments (which Lightning handles). Different layers need different privacy and sovereignty models.

— If you use a Payjoin-enabled wallet like Cake or Bull Bitcoin, on-chain privacy now works automatically in the background without user friction—no need to download a separate app or take extra steps.

— For developers building Bitcoin applications, consider delegating settlement to established SDKs (Breeze SDK) rather than building Payjoin from scratch; the interactivity layer works best when many wallets share the same infrastructure.

— Monitor Cross-Input Signature Aggregation (CISA) progress alongside Payjoin; the two protocols synergize to improve both batching efficiency and privacy fingerprinting over time.