🕵️‍♂️ Sealed Bid Auction – Solidity Smart Contract

This repository contains a Sealed-Bid, Two-Phase Auction smart contract written in Solidity. Participants submit encrypted (sealed) bids during the bidding phase and reveal them in the reveal phase. This preserves privacy and fairness until all bids are disclosed. The highest valid bid wins, and the winner’s funds are transferred to the beneficiary at the end of the auction.

🔑 How It Works

The auction occurs in two distinct phases:

Bidding Phase

Users submit a sealed bid (a hash of their actual bid amount, legitimacy flag, and a secret).

The bid is accompanied by a deposit (must be ≥ potential bid).

Reveal Phase

Users reveal their actual bid, whether it's legitimate (true/false), and their original secret.

If the reveal matches the hash and is valid, the bid is considered for winning.

The highest valid bid becomes the winner.

📦 Features

Sealed Bidding: Prevents front-running or early disclosure of bid amounts.

Two-Phase Auction: Encourages fair play by separating commitment and reveal.

Refund Mechanism: Participants reclaim excess deposit or lose nothing if their bid is invalid.

Safe Withdrawals: Outbid users can safely withdraw their deposits.

Secure Finalization: Only callable once, ensuring funds go to the beneficiary.

🧾 Contract Details

Parameter Description beneficiary Recipient of the winning bid funds biddingEnd Timestamp marking the end of the bidding phase revealEnd Timestamp marking the end of the reveal phase highestBid Current highest valid bid revealed highestBidder Address of the top bidder pendingReturns Tracks withdrawable amounts for users who were outbid

⌛ Phases and Timeline

Bidding Phase: Submit a sealed bid (hash) with a deposit → ends at biddingEnd.

Reveal Phase: Reveal bid amount, flag, and secret to validate → ends at revealEnd.

End Auction: Finalize auction and transfer funds to beneficiary.

⚙️ Core Functions

• bid(bytes32 _sealedBid) Submit a hashed (sealed) bid with ETH deposit.

Only allowed before biddingEnd.

• reveal(uint _bidAmount, bool _isLegit, string _secret) Reveal the bid after bidding has ended.

Validates bid hash, legitimacy, and deposit size.

Updates the highest bid if valid.

• auctionEnd() Callable only after the reveal phase.

Transfers the highest bid to the beneficiary.

• withdraw() Allows non-winning bidders to withdraw unused deposits.

• generateSealedBid(uint, bool, string) Public utility function for off-chain hash generation.

📤 Events

AuctionEnded(address winner, uint256 amount): Emitted once at the end of the auction.

🧪 How to Use (Simplified)

• Off-chain: Generate sealed bid hash keccak256(abi.encodePacked(bidAmount, isLegit, secret))

• On-chain:

Call bid() with the sealed hash and ETH deposit.

Wait until biddingEnd.

• Reveal:

Call reveal(bidAmount, isLegit, secret) during reveal phase.

Contract checks your hash and updates the winner.

• Finalize:

Anyone can call auctionEnd() after revealEnd.

• Withdraw:

Losing bidders can reclaim funds via withdraw().