Sweepstake

Run a Gumball as a no-loss draw: any number of collectors enter during a set window, a public random beacon picks the winners on chain, and every other entry is refunded.

The mallow Sweepstake program (sWEEpg22uXSMaDx9QjdVKeUaZtk2Vj19XusBeszTiTQ) holds every entry's funds in escrow and decides each result. Anyone can verify a draw.

Setup
Before start
Creator signs the guard update. The terms are committed on chain.
Entries open
1 hour to 7 days
One entry per wallet. Funds go into escrow.
Draw
Close + 30 s
The drand round is verified on chain and the winners are fixed.
Delivery
Right after the draw
mallow mints each prize to its winner. Everyone else is refunded automatically.
Recovery
Day 7 onward
Any open entry gets everything back, fee included.

Cancelled

Only before entries close: by the creator while there are no entries, or by anyone if the machine was tampered with. Everyone is refunded in full.

Void

The draw never settled by day 3. Everyone is refunded in full.

Days count from the moment entries close.

Entering

You enter

Deposit, rent and the 0.011 SOL entry fee go into escrow.

The draw picks k winners

k = the smaller of the entry count and the artwork count.

Won

mallow delivers your artwork to your wallet. If it takes over 5 min, you can claim it yourself.

Not selected

Deposit and rent come back automatically. Withdraw now if it takes over 15 min.

Still open on day 7?

Recover deposit returns everything, fee included. No proof is needed.

The entry modal shows the full cost before you sign:

Item	If you're not selected
Deposit: the ticket price	Refunded
Account rent: for the artwork's account and your entry	Refunded
Entry fee: 0.011 SOL	Not refunded
Estimated network fee	Not refunded

One entry per wallet. Entries are final
Tickets are numbered from #1 in order of entry
If the payment token has a freeze authority, the modal warns you: a freeze can hold up your entry, mint or refund
If you win, the button shows Delivering to your wallet... while mallow mints your artwork. If it hasn't arrived after 5 minutes, the button becomes Claim artwork and you can mint it yourself
If the machine can no longer mint, the page shows Delivery failed, and the entry is recovered in full on day 7

Creating a Sweepstake

Who: verified creators, in New artwork mode. Pre-minted and burn-requirement Gumballs can't run one
How: choose Sweepstake as the Allowlist type. There are no allowlist phases, and each wallet gets one entry
Price: one ticket price, in SOL or a supported SPL token (Token-2022 included)
Timing: a scheduled start at least 2 minutes away. Entries stay open for 24 hours, 48 hours or a custom length between 1 hour and 7 days
Artworks: all must be loaded before it goes live. Leftover artworks after the draw stay unminted

The last step of creating asks you to sign a guard update. It blocks minting until entries close, lets only the Sweepstake program approve a mint, and hands it the guard's authority, so no one can change the guard while the sweepstake is live. If you skip it, the studio shows Setup pending until you sign.

	Before the first entry	After the first entry	After entries close
Edit price, start, duration or artworks	Yes, with one re-signed guard update	No	No
Cancel Sweepstake (creator)	Yes	No	No
Cancel for tampering (anyone)	Yes	Yes	No

A cancel for tampering needs proof on chain that the machine changed: its mint authority, an artwork minted, or its artwork count. Every entry is then refunded in full. While setup is pending, Remove Sweepstake turns it back into a normal Gumball.

How the Draw Works

Public inputs

drand randomness

Round fixed at creation. Its signature is verified on chain. Randomness = SHA-256(signature).

Sweepstake identity

Program, sweepstake, machine, setup ID, drand chain and round.

Entry counts

n = entries at the draw. k = min(n, artworks).

Seed

32 bytes, stored on chain when the draw settles. It can't be reused for another sweepstake.

Shuffle each ticket index

Swap-or-not shuffle, 90 rounds. A ticket wins when its shuffled position is below k, so exactly k win.

Manifest

Public JSON with every input, entrant and result. Its SHA-256 is the evidence hash.

Numbers match the verification steps below.

Unpredictable: the drand round is the first evmnet round starting 30 seconds after close. It is fixed before entries open, and no one can know its value until it's published
Unreusable: the seed binds the program, the sweepstake, the machine and its setup, so a round can't be replayed for another draw
Fixed: the draw settles once. It freezes the entry count, and no entries are accepted after it
Fair: the shuffle is a permutation, so exactly k tickets win and every ticket has the same chance

Verifying a Draw

You don't have to trust mallow. Open Draw details on the Gumball page for the values you need:

Field	Meaning
Draw round	The committed drand `evmnet` round
Seed	The seed the program stored (hex)
drand randomness	SHA-256 of the round's signature (hex)
Winners	`k of n`
View manifest	The public draw manifest, once every entry has closed
Evidence hash	SHA-256 of the manifest file

Tickets on the page start at #1. The manifest and the script below use the index, which is the ticket number minus 1.

Check the drand Round

curl https://api.drand.sh/04f1e9062b8a81f848fded9c12306733282b2727ecced50032187751166ec8c3/public/<round>

randomness must equal drand randomness, and must be the SHA-256 of signature. The round must be the first one starting at or after close + 30 s: round r starts at 1727521075 + (r − 1) × 3.

Recompute the Seed

SHA-256 of the public inputs, concatenated. Every field is in the manifest.

Recompute the Winners

Shuffle each ticket index with the seed. A ticket wins when its position is below k. If k ≥ n, every ticket wins.

Check the Manifest

curl -s <manifest-url> | sha256sum

The output must equal Evidence hash. When the sweepstake's account closes, a second manifest adds the closing transaction; the first stays online unchanged.

Run It All at Once

This script runs steps 1 to 4 against a manifest. It needs Node.js 20 or newer and nothing else.

# Whole draw: every line prints true
npx tsx verify-draw.ts <manifest-url> <evidence-hash>

# One ticket, before the manifest exists
npx tsx verify-draw.ts ticket <seed> <n> <k> <ticket-index>

To also check the drand BLS signature and every transaction against the chain, use the open-source SDK verifier with any full-history Solana RPC:

npx -p @mallow-labs/mallow-sweepstake-sdk mallow-sweepstake verify <sweepstake-address> --rpc <rpc-url> --drand-mirror
npx -p @mallow-labs/mallow-sweepstake-sdk mallow-sweepstake verify-manifest <manifest-url> --rpc <rpc-url>

The sweepstake address is sweepstake in the manifest.

Trust Model

Enforced by the Program

The committed drand round and its signature check
The seed, which entries win, and exactly k winners
Escrow of every entry's funds, the deadlines and the fee rule
Refunds only ever go to the wallet that entered

Trusted

mallow to countersign entries and prize mints, and to deliver or refund on time. From day 7 you can recover everything yourself
The creator not to stop mints by moving the mint authority, withdrawing the machine or changing the collection delegate. Before close this cancels the sweepstake; after, the entry recovers in full on day 7
drand and the program's upgrade authority
The payment token's issuer, since a freeze can delay token transfers

Ready to run a sweepstake? Head to the Create page to set up a Gumball.

Seed byte layout (233 bytes)

Shuffle algorithm

verify-draw.ts

Derive the sweepstake address from the Gumball address

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