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Dan Gould: Payjoin DevKit Ships and Breaks Common Input Ownership | SLP753 — Key Takeaways

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Dan Gould: Payjoin DevKit Ships and Breaks Common Input Ownership | SLP753

Stephan Livera18mJul 7, 2026

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PayJoin DevKit 1.0 enables wallet teams to integrate async, serverless PayJoin (BIP77) in a weekend, with Bull Bitcoin and Cake Wallet already live in production.

Key takeaways

Async PayJoin uses untrusted mailbox + OHTTP to remove server requirement

Async PayJoin uses untrusted mailbox + OHTTP to remove server requirement

  • BIP77 stores encrypted, fixed-size blobs on a third-party directory; neither party needs a live TLS endpoint or hot wallet server.
  • OHTTP relay decouples IP from blob: directory sees only ciphertext, relay sees only IP — correlation attack requires compromising both.

PayJoin DevKit 1.0: wallet PayJoin integration in a weekend

PayJoin DevKit 1.0: wallet PayJoin integration in a weekend

  • PDK abstracts protocol state, OHTTP relay, and transaction construction — wallet dev handles DB serialization, network messages, and coin selection config only.
  • Bull Bitcoin and Cake Wallet are live pilots; reference impl connects to Bitcoin Core via payjoin-cli.

PayJoin V2 breaks common-input heuristic but leaves wallet fingerprints intact

PayJoin V2 breaks common-input heuristic but leaves wallet fingerprints intact

  • Timing clusters (e.g., East Coast vs. Sydney activity windows) and wallet-specific script patterns remain exploitable by chain surveillance firms.
  • Full privacy requires multi-party batching (roadmap phase 3); V2 is a necessary but insufficient step.

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In this video

  1. 1mIntroduction and PayJoin DevKit 1.0 Update
  2. 1mWhat Is PayJoin: Elevator Pitch
  3. 3mCurrent Adoption and V1 vs V2 Protocol
  4. 7mHow Async PayJoin Works in Practice
  5. 10mDeveloper Integration and Infrastructure
  6. 14mPrivacy Limitations and Wallet Fingerprinting
  7. 17mFee Savings and Net Settlement Benefits
  8. 17mFuture Roadmap and Call to Action

“I think, unfortunately, Shinobi is more right than he is wrong when it comes to basic pay join.”

— Dan Gold

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