Bluff and Barrel : On-Chain Deception Game

A fully on-chain, FHE-encrypted 4-player card bluffing game with Russian Roulette elimination and USDC stakes. Built on Fhenix CoFHE. Deployed on Arbitrum Sepolia.

What is Bluff and Barrel?

A provably fair on-chain card bluffing game where:

• Cards are encrypted : nobody can see your hand, not even the contract

• Bluffs are verified cryptographically : no trusted server, no oracle

• The revolver is real : bullet position is FHE-encrypted, unknown until it fires

• Stakes are real : USDC wagers with automatic winner payout

• Everything is provably fair : powered by Fhenix Fully Homomorphic Encryption

Game Modes

How to Play

1. Choose your character (8 animal masks) and set USDC stake (or play free)

2. Create or join a table (4 players required)

3. Each round: a target card is announced (Ace, King, or Queen)

4. On your turn: play 1-3 cards face-down, claiming they're the target

5. Other players: believe you or call "LIAR!"

6. If challenged: cards are revealed via FHE decryption — everyone sees the actual cards

7. Russian Roulette: 6 chambers, 1 bullet, position unknown

8. Last player alive wins the pot (stake x 4, minus 5% platform fee)

Architecture

Syetem

Contract Architecture

FHE Data Flow

Basic Game flow

Deployed Contracts (Arbitrum Sepolia)

Shared In all modes

Basic Mode

Devil Mode

Chaos Mode

FHE Integration

All encrypted values are computed on-chain through Fhenix CoFHE operations. Your hand remains encrypted until you explicitly permit decryption challenge reveals and spin outcomes use allowPublic() to broadcast results without exposing intermediate secrets. The bullet position stays fully encrypted until the revolver fires, ensuring no player (not even the contract) knows the outcome before the moment of truth.

FHE Operations Per Game

Grand total per game ~1,200 FHE Operations Per Game

USDC Stake System

• Table creator sets stake amount (0 = free game)

• Each player deposits USDC on join (ERC20 approve + transferFrom)

• Winner receives 95% of pot (stake x 4 players)

• 5% platform fee sent to treasury

• Automatic payout on GameOver no manual claim needed

Tech Stack

Contracts: Solidity 0.8.28, Hardhat, @fhenixprotocol/cofhe-contracts, viaIR

Frontend: Vite, React 18, TypeScript, wagmi v2, viem, @cofhe/sdk, Zustand, Tailwind CSS, Framer Motion

Network: Arbitrum Sepolia (Chain ID: 421614)

FHE: Fhenix CoFHE (Threshold Network decryption)

Game Modes Detail

Basic Mode

• 20 cards: 6 Ace, 6 King, 6 Queen, 2 Joker (wild)

• 5 cards per player, play 1-3 per turn

• Loser of challenge spins own revolver

Devil Mode

• Same as Basic + 1 Devil Card (replaces one table-type card)

• Devil can only be played alone

• If challenged and Devil revealed: ALL other players face Roulette

Chaos Mode

• 12 cards: 5 King, 5 Queen, 1 Master, 1 Chaos

• 3 cards per player, play exactly 1 per turn

• Winner of challenge shoots an opponent of choice

• Master card: accused gets to shoot someone

• Chaos card: ALL players shoot simultaneously

Features

• 8 selectable character masks (on-chain storage)

• Card reveal on challenge (actual card images shown)

• Per-player revolver with chamber indicators

• 60-second turn timer with on-chain forceTimeout()

• Dramatic overlays (LIAR!, CLICK, BANG, Winner with wallet address)

• Mode selector (Basic/Devil/Chaos) in lobby

• USDC stake with automatic payout (5% platform fee)

• Rules info button in lobby and game

• WebSocket relay for real-time sync (3s polling fallback)

• Multi-wallet support (MetaMask, Phantom, Rabby, Coinbase, etc.)

• Security audited checked transfer returns, access controls, participant validation

Documentation

CONTRACTS.md FHE and contract implementation details

TESTING_GUIDE.md Step-by-step testing guide

How it started

Started as a minimal 2 player proof of concept to validate FHE encraypted card dealing and challenge verification was technically feasible on Fhenix CoFHE. The first working version had:

A single solidity contract with hardcoded 2 players

Phase 1 : Core Mechanics

• LiarsBarDeck: encrypted 20-card shuffle using FHE.randomEuint8 + draw-without-replacement via FHE.selec chains

• LiarsBarRevolver: per-player encrypted bullet position (1-6), chamber pointer, beginSpin → publishSpinResult

• LiarsBarGame`: minimal state machine WaitingForPlayers → Dealing → PlayerTurn → Challenging → Spinning → GameOver

• Challenge verification: verifyClaim returns ctHash of ebool, frontend decrypts and pushes result back

Initial Version Demo Video: V1 Bluff and barrel demo

Phase 2 : 4 players and Updated UI

• 🦊🐰🐱🦉 Animal mask avatars

• Per-player revolver chamber indicators

• Dramatic "LIAR!" challenge overlay with card reveal

• Full-screen CLICK/BANG trigger pull animation

• 30-second turn timer with visual countdown

• Game event log

Version 2 Demo Video: V2 Bluff and Barrel demo

Phase 3 : Two more card game types (Devil and Chaos) with custom UI assets

• Character selection (8 animal masks) stored on-chain in Player struct

• Lobby: create game, join by ID, stake USDC (approve flow)

• Game room: card hand display, play cards, call liar, pull trigger

• Challenge overlay with card reveal showing actual card images

• Spin animation with revolver visual

USDC Stakes

• Integrated Circle USDC ERC-20 on Arb Sepolia

• Creator sets stake amount, players approve + deposit on join

• Auto-payout to winner: 95% of pot, 5% platform fee

• getStakeAmount view so joiners see the wager before committing

Devil Mode

• New LiarsBarDevilDeck: 5 table-type + 1 Devil(4) + 6 + 6 + 2 Joker = 20 cards

• New LiarsBarDevilGame: added MultiSpinning state

• Devil card in played hand → ALL other alive players spin simultaneously

• triggerMySpin per player, multiSpinCtHashes mapping, auto-resolve when last spinner submits

• Frontend: mode selector in lobby, MultiSpinning UI with per-player trigger buttons
  

Chaos Mode

• New LiarsBarChaosDeck: 12 cards (5 King + 5 Queen + 1 Master + 1 Chaos), 3 cards per hand

• New LiarsBarChaosGame: added Targeting / MultiTargeting / Shooting states

• Three outcomes on challenge: regular card → challenger shoots, Master card → accused shoots, Chaos card → everyone shoots simultaneously
  chooseTarget / chooseTargetMulti, spinForTarget on the Revolver

• Frontend: targeting UI with alive player selection, only relevant player sees buttons

Polish + Infra

• WebSocket relay server for real-time state sync (Node.js, port 8080)

• Sound effects (card play, liar call, spin, bang/click, game over) Mute toggle in nav

• invite links: ?join=ID&mode=MODE pre-fills lobby

• Roadmap page at /roadmap

• Share result at game over: download PNG + share on X

• 60s turn timer with forceTimeout() on-chain
  
  

Security Audit + Bug Fixes

Critical contract fixes:

• Unchecked USDC transfers → require(usdc.transfer(...))

• Access control on publishChallengeResult → participant-only check

• onlyGame modifier on revolver publish functions

• Dead players dealt to address(0) not first player

Frontend fixes:

• Stale CoFHE permits removed before creating new ones

• Wallet address change detection resets FHE client

• Auto-retry on 503/gas errors (4 attempts with backoff)

• Challenge overlay clears stale card data on state transitions

Gas + Stability

• Identified eth_estimateGas returns garbage for FHE txs on Arb Sepolia

• Adopted per-function explicit gas limits (like CofhePoker pattern)

• Split _startRound (FHE deal) into separate dealNextRound tx to prevent spin+deal in one tx exceeding gas

• 2x baseFee floor for maxFeePerGas to prevent "less than baseFee" errors

Final State (Arbitrum Sepolia)

Functional Contracts (7 total)

• Revolver: 0x1E83b93AF872BE24e6fD642640943fFebb9374d6

• Basic Game: 0x0E2bFBC7124A0313E27172A1d7eb28136e45580F

• Basic Deck: 0xA3FCd7571BC9A9f2ABB14BFDc4198D181dFC830e

• Devil Game: 0x8b2c2C97Db8AbA07fb4790BE2A9D40635E3a6642

• Devil Deck: 0x81631728A254B8d0aFf531615c35Ab728D54f61b

• Chaos Game: 0x27C2E979EC550d1a2F6c637aE508640405227F9F

• Chaos Deck: 0x406ba0147Fa54809048cbE6F6813c02504D77951

What works:

• Basic mode: fully playable end-to-end (tested with 4 players)

• All 3 modes deployable and joinable

• USDC stakes functional

• Character selection, card reveal, spin animation all working

• WebSocket real-time sync working

Known limitations (Arb Sepolia):

• Devil/Chaos multi-spin resolution consumes too much gas per tx (FHE deal + spin in same block)

• MetaMask shows inflated fee estimates for FHE-heavy txs

• dealNextRound workaround partially resolves the gas issue but not fully stable

Key Technical Numbers

• ~1,200 FHE operations per full game (5 rounds, 4 players)

• 20-card encrypted shuffle: ~200 FHE ops (draw-without-replacement)

• Challenge verification: ~40 FHE ops (per played card: eq + or + and)

• Spin: ~3 FHE ops (eq + add + rem)

• Gas per `startGame` (deal): ~7.9M gas on Arb Sepolia