Zero-Knowledge Blackjack

This is a zero-knowledge proof application built on Soroban for the hack-a-soroban-winter-2023.

Link to demo slides

Game Description

Start with 3 random cards, each with a number between 1 and 14. The goal is to get their sum as close to 21 points without exceeding it.

Allowed player actions

• STAND(0): do nothing
• HIT(1): ask for another card, with the risk of going over 21

The key rule:

If the current sum is already > 21, you shall not draw another card (action must be "STAND")

How to Run

1. Install Soroban Install soroban-tools following instructions from https://github.com/jayz22/soroban-tools/tree/zk-hackathon

2. Build the contracts

• Run make build
• cd target/wasm32-unknown-unknown/release You should see two contracts:
• Player (prover) contract: player.wasm
• Dealer (verifier) contract: dealer.wasm

3. Deploy the contracts

• soroban deploy --wasm player.wasm --id aaaa1 --ledger-file ledger.json this deploys the player contract in the sandbox mode. It generates the contract ID 00000000000000000000000000000000000000000000000000000000000aaaa1 for the player contract, and a ledger file ledger.json that persists the ledger state.
• soroban deploy --wasm dealer.wasm --id dddd0 --ledger-file ledger.json same as above, with dealer contract ID 00000000000000000000000000000000000000000000000000000000000dddd0

4. Draw cards

• Invoke the player contract: soroban invoke --id 00000000000000000000000000000000000000000000000000000000000aaaa1 --fn draw_cards --ledger-file ledger.json. This pseudo-ramdomly generates three cards. (The pseudo ramdom function is very naive and not intended for production, only for this demo.)

5. Make a decision

• Invoke the player contract: soroban invoke --id 00000000000000000000000000000000000000000000000000000000000aaaa1 --fn decide --arg 1 --ledger-file ledger.json. The decision follows --arg. 0 means to STAND and 1 means to HIT.

6. Verify the decision

• Invoke the dealer contract passing in the player contract's ID: soroban invoke --id 00000000000000000000000000000000000000000000000000000000000dddd0 --fn verify --arg 00000000000000000000000000000000000000000000000000000000000aaaa1 --ledger-file ledger.json. This will display either TRUTH if the player action was legal or LIE if otherwise.

Enjoy!