OpenChainGraph Suite · ART-583 · Public-Infrastructure Verification

Beacon-Seeded Fair-Sampling Deriver

Derives a deterministic audit sample from a public randomness beacon pulse, drand's quicknet chain or a NIST NISTIR-8213 randomness beacon, and a pre-committed hash of the item manifest being sampled. NIST names exactly this the canonical use of a public randomness beacon: preventing an auditor from biasing a selection, or from being accused of doing so. Election risk-limiting audits (RLAs) run the same ceremony. Selection uses only SHA-256/HMAC, an HMAC-DRBG walk, with no randomness of its own, no clock, nothing hidden. Anyone holding the same three declared inputs (manifest hash, pulse, algorithm id) can replay the identical selection offline from the derivation transcript below.

HMAC-DRBG (SHA-256 only)drand quicknet / NISTIR-8213Offline-replayable transcript
🔒 All inputs are processed locally in your browser. No data is transmitted. Do not enter real personal data — use synthetic or anonymised inputs only.
The Ceremony: Order Matters

The fairness of this sample depends entirely on doing these three steps in order, before you touch this page:

  1. Fix the population first. Freeze the exact item list to be sampled and hash it (any stable canonical hash of the manifest works; SHA-256 of the sorted item list is typical). Publish or otherwise commit to that item_manifest_hash before the next step.
  2. Wait for a beacon pulse you did not choose. Take the NEXT round of a public randomness beacon after your commitment: drand's quicknet chain (a new pulse roughly every 3 seconds, verifiable output published openly) or a NIST NISTIR-8213 randomness beacon pulse. Paste that round's declared randomness value below exactly as published.
  3. Derive, don't re-roll. This page derives the sample once, deterministically, from the manifest hash and the pulse. If the result is inconvenient, the correct response is never to re-run with a different pulse: that is the cherry-picking this ceremony exists to prevent.

Precedent: NIST's Interoperable Randomness Beacons project names bias-resistant audit sampling as a beacon application; U.S. election jurisdictions running risk-limiting audits (e.g. Colorado, per the U.S. Election Assistance Commission's RLA guidance) draw ballot samples from a public dice roll or beacon for the identical reason. drand quicknet is treated as the primary beacon here (sub-3-second cadence, no single operator); a NISTIR-8213 pulse serves as a corroborating co-seed when both are available.

Declared Inputs
Paste the beacon's published randomness for the round above, not a value you generate.
The hash you committed to (published, timestamped, or otherwise fixed) before waiting for the pulse. This ordering is what makes the sample cherry-pick-proof.
Selected Indices
Seed (HMAC-SHA256 of pulse under the manifest-hash key)
Execution Hash (SHA-256)