# `gno.land/p/moul/x/daily/commitreveal/v0`

**Commit–reveal scheme** — `Commit`, `MustCommit`, `Verify`, `Open`,
`ValidCommitment`, `MinSaltLen`, `MaxValueLen`, `DigestLen`.

```go
import "gno.land/p/moul/x/daily/commitreveal/v0"

c, _ := commitreveal.Commit("rock", "alice-secret-salt-1") // phase 1: publish c
commitreveal.Open(c, "rock", "alice-secret-salt-1")        // phase 2: nil
commitreveal.Open(c, "paper", "alice-secret-salt-1")       // ErrMismatch
```

A transaction is public before it executes, so a naive sealed-bid auction or
simultaneous-move game lets whoever moves last read everyone else's move and win
for free. Commit–reveal splits the action: publish `H(value ‖ salt)` first, open
it later.

**The salt is enforced, not advised.** Rock-paper-scissors has three possible
moves, so an unsalted commitment has three possible hashes and is broken by
trying all of them. `Commit` refuses a salt shorter than `MinSaltLen` (16), and
`Verify` enforces the same floor — a short salt cannot be smuggled past it.

Two details that are easy to get wrong, both tested:

- **Length-prefixed hashing.** With plain concatenation `("ab","cd…")` and
  `("abc","d…")` produce identical bytes, so one commitment could be opened two
  different ways. The lengths are hashed in.
- **Constant-time digest comparison.** A short-circuiting check leaks, through
  timing, how many leading bytes of a guess were right — enough to reconstruct a
  commitment byte by byte.

This package computes and checks commitments. It stores nothing and knows nothing
about phases or deadlines; the realm owns that.

**Live demo:** [`r/moul/x/daily/commitrevealdemo`](https://github.com/moul/gno-contracts/tree/main/r/moul/x/daily/commitrevealdemo/v0)
· render it at [`/r/moul/x/daily/commitrevealdemo/v0`](https://gno.land/r/moul/x/daily/commitrevealdemo/v0).

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Part of **[moul/gno-contracts](https://github.com/moul/gno-contracts)** — moul's versioned gno.land contracts. See the repository for the full catalog, build/test tooling, and usage.

> 🧪 **Highly experimental — potentially vibe-coded.** Not audited; may break, change, or be removed at any time. Do not use with anything of value. Full disclaimer: [DISCLAIMER](https://github.com/moul/gno-contracts/blob/main/DISCLAIMER.md).

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