Presentation Order Draw

A public draw for presentation slots, built from repeated SHA3-512 hashing. Each group fixes its number of iterations before the input is known.

Commitment schemesHash chainsEntropy sourcesdemo

Objectives

Compute a slot value from the canonical input by iterating SHA3-512 over raw bytes.
Explain why the timestamp and the reading must freeze before anything is computed.
Derive the deal from the reading and show that it is reproducible from the published record.
Predict what a group could do if it chose its iteration count after seeing the reading.
Produce a record that lets anyone else recompute the same result.
Recompute one published row from its five fields and compare it against the posted digest.

25%

The lottery that assigns presentation slots, run live and recomputable afterwards by anyone. Each group brings a name, a topic, and an iteration count committed in advance. The timestamp and the reading are taken in the room, and each group is dealt one value of that reading.

NONCE = the one reading value this group was dealt; canonical = "TIMESTAMP|NAME|TOPIC|NONCE"; h(0) = utf8(canonical); h(i+1) = SHA3-512(h(i)) for i = 0 … N−1; value = first 5 hex characters of h(N). Ascending value takes the earliest slot.

Draw board

Animate the reorder

The reading, shared by every group

○ Not connected

Cloudflare's LavaRand pool, served as bytes.

Waiting for the first response. If it does not arrive, the board falls back to typed entry.Each group is dealt one value of this reading, by a shuffle seeded with the reading itself. Nobody learns which value they get until the reading exists. This reading is nobody can predict it, and the server is the one choosing it. Pick one source, press once, and take what comes: pressing again until you like the reading is the same grinding attack, run from this side of the room.

Timestamp (epoch ms)

starting

Group

Name for group 1

Topic

Topic for Group 1

Nonce

dealt on calculate

Iteration count for Group 1

Value

not drawn

Timestamp (epoch ms)

starting

Group

Name for group 2

Topic

Topic for Group 2

Nonce

dealt on calculate

Iteration count for Group 2

Value

not drawn

Timestamp (epoch ms)

starting

Group

Name for group 3

Topic

Topic for Group 3

Nonce

dealt on calculate

Iteration count for Group 3

Value

not drawn

Timestamp (epoch ms)

starting

Group

Name for group 4

Topic

Topic for Group 4

Nonce

dealt on calculate

Iteration count for Group 4

Value

not drawn

Timestamp (epoch ms)

starting

Group

Name for group 5

Topic

Topic for Group 5

Nonce

dealt on calculate

Iteration count for Group 5

Value

not drawn

N is committed before the reading is taken. Each group submits its own count, 10 to 1000, in Canvas before the reading exists. That ordering is what stops a group trying all 991 counts against a known nonce and keeping the slot it liked.

The name is hashed too. Type it exactly as Canvas will publish it: a different name is a different slot. Two groups may not share one, because the deal is keyed on the name.

✗ The reading is empty.

The record

Nothing is drawn yet. Press Calculate above and the record appears here, with everything anyone needs to recompute it.

Check a published row

Type one row of a published record back in. The digest is recomputed here, in your own browser, under the same rule the board used, and nothing on this card touches the draw above. Then paste the digest the record published and this says whether the two agree.

Timestamp (epoch ms)

Timestamp

1970-01-01T00:00:00.000Z

Group

Group name

Lowercased and sorted before hashing, so case and member order do not matter.

Topic

Nonce

Nonce dealt to this group

One value, not the whole reading.

Iteration count

◌ Type the timestamp the record published.

Full digest as published, to compare against

The order of operations is the protocol. A commitment binds you to a value before you learn what would let you exploit it. Reverse the two steps and a group can compute all 991 outcomes and publish the one it wanted, and every number still verifies.

The timestamp and the nonce freeze when the button is pressed, because a draw whose inputs keep moving cannot be recomputed. A five-character value is 2²⁰outcomes, so the tie rule is fixed in advance, on the full 512-bit digest.

step 1/4

CPE 645 / CS 685

Presentation Order Draw

The reading, shared by every group

Tests Cannot See Prediction

A Block Cipher Is a Permutation

The reading, shared by every group