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CHIP-0057: Silent Payments#198

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CHIP-0057: Silent Payments#198
kdc2000 wants to merge 5 commits into
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@kdc2000 kdc2000 commented Mar 31, 2026

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@danieljperry danieljperry changed the title chip-kdc2000-silent_payments CHIP-0057: Silent Payments Mar 31, 2026
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danieljperry commented Mar 31, 2026

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This CHIP has been assigned as CHIP-57 and is a Draft. It describes a method to support Unlinkable on-chain payments to a static address using ECDH on BLS12-381.

Please leave your reviews here, and feel free to comment in the #chips channel of our Discord.

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danieljperry commented May 14, 2026

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The recording of the discussion of this CHIP is now available on Youtube.

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danieljperry commented May 14, 2026

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This CHIP is now in Review. Please leave your reviews here, and be sure to watch the video discussion, linked above.

@kdc2000
CHIP-0057: collapse scanning to a single opcode-64 Pass 2 + editorial…
d8aa149 
… fixes

Reconcile the spec to the simplified single-Pass-2 scanning model (v1.5):
- Collapse Pass 2a (puzzle-hash grouping) + Pass 2b into a single Pass 2
  (opcode-64 ASSERT_CONCURRENT_SPEND directed-SCC); drop puzzle-hash grouping.
- Reword the stale "Spend group" glossary definition to concurrent-spend linkage.
- Correct Appendix A bandwidth for Chia's ~1-in-3 transaction-block frequency
  (~1,536 tx blocks/day; ~7.5-9 MB/day total).
- Remove Appendix C (ECDH scalar multiplication).
- Genericize evolving reference-implementation file references.

Status unchanged (Review). Test Vector 4 cryptographic values unchanged.
@kdc2000

kdc2000 commented Jun 3, 2026

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Update on the multi-input grouping, plus a few editorial corrections.

Grouping: strongly connected components over ASSERT_CONCURRENT_SPEND

While implementing silent payments in the chia-wallet-sdk, I adopted strongly-connected-component (SCC) grouping over explicit opcode-64 ASSERT_CONCURRENT_SPEND bindings, and updated the CHIP to match. The scanner builds a directed graph from the ASSERT_CONCURRENT_SPEND conditions in each removal's solution and treats each strongly connected component as a multi-input group.

This replaces the earlier approach, which combined two heuristics: grouping coins that share a puzzle hash, and linking coins via coin announcements (opcode 60/61, CREATE_COIN_ANNOUNCEMENT / ASSERT_COIN_ANNOUNCEMENT). The single SCC mechanism is the one I validated against the SDK implementation.

Test Vector 4's cryptographic values are unchanged.

Editorial corrections

  • Appendix A (bandwidth): corrected for Chia's transaction-block frequency — only ~1 in 3 blocks carries spends (~1,536 tx blocks/day, not ~4,608); daily figures recomputed (~7.5–9 MB/day total).
  • Appendix C (ECDH scalar multiplication): removed — an implementation performance note rather than protocol content.
  • Glossary: reworded the "Spend group" definition.
  • Reference Implementation: framed as illustrative example code (not normative); dropped specific filenames since the example layout evolves.
  • Minor wording in the Indistinguishability section.

Status unchanged (Review).

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@kdc2000 @danieljperry