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sinsemilla-formal\n\n**Status:** Fully proven — zero `sorry` statements.\n\nLean 4 formalization of the Sinsemilla hash function from Zcash's Orchard protocol, with a machine-verified security reduction to the discrete logarithm problem on the Pallas curve.\n\n## What's formalized\n\nSinsemilla splits a bit message M into 10-bit chunks and accumulates elliptic curve points: Acc_{i+1} = [2]·Accᵢ + S(mᵢ), starting from Q(D) = GroupHash(D).\n\n**Key results:**\n\n- **`hashToPoint_pedersen`** — the hash equals [2ⁿ]·Q(D) + Σᵢ 2^(n−1−i)·S(mᵢ): a Pedersen vector commitment.\n- **`chi_injective`** — distinct equal-length chunk sequences produce distinct coefficient vectors.\n- **`collision_implies_sumChunks_eq`** — a collision on equal-length messages yields a DLP relation on Pallas.\n\n## Axioms\n\n| Axiom | Justification |\n|-------|--------------|\n| `groupHash_ne_zero` | Requires full SWU map + BLAKE2b formalization |\n\n## Build\n\n```shell\nlake build\n```\n\n## Dependencies\n\nLean 4 (`v4.30.0-rc2`), [Mathlib4](https://github.com/leanprover-community/mathlib4), [pasta-formal](https://github.com/oxarbitrage/pasta-formal).\n\n## References\n\n- [Zcash Protocol Spec §5.4.1.9](https://zips.z.cash/protocol/protocol.pdf)\n- [Halo 2 — Sinsemilla gadget](https://zcash.github.io/halo2/design/gadgets/sinsemilla.html)\n\n---\n\n## Part of a series\n\nSix repositories formally verifying the Zcash Orchard cryptographic stack:\n\n| Layer | Repository |\n|-------|-----------|\n| Curves | [pasta-formal](https://github.com/oxarbitrage/pasta-formal) |\n| Hash | [poseidon-formal](https://github.com/oxarbitrage/poseidon-formal) |\n| Hash-to-curve | [sinsemilla-formal](https://github.com/oxarbitrage/sinsemilla-formal) |\n| Signatures | [redpallas-formal](https://github.com/oxarbitrage/redpallas-formal) |\n| Protocol | [orchard-formal](https://github.com/oxarbitrage/orchard-formal) |\n| Proof system | [halo2-formal](https://github.com/oxarbitrage/halo2-formal) 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